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High-resolution model-projected changes in mid-tropospheric closed-lows and extreme rainfall events over Southern Africa
International Journal of Climatology
Abstract
Mid-tropospheric closed-lows (cold-core cut-off lows and warm-core tropical lows) are important rain producing weather systems for the southern Africa region. Over South Africa, most wide-spread flood events are caused by these systems. It is therefore important to explore the potential impact of anthropogenic forcing on the occurrence of closed-lows and extreme rainfall events over the region. Coupled global circulation models (CGCMs) can not be directly applied for this purpose because of their relatively low spatial resolution—some form of downscaling is required to adequately resolve these systems and the rainfall they cause. In this study, a variable-resolution atmospheric global circulation model is applied as a regional climate model to simulate closed-low characteristics over southern Africa under current and future forcings. The model is forced with greenhouse gas concentrations according to the A2 SRES scenario and with sea surface temperatures (SSTs) and sea-ice as specified by the CSIRO Mk3 CGCM. The model projects a general decrease in closed-low frequencies over the region, which occurs in association with a general strengthening of the subsiding branch of the Hadley cell. However, the climate-change signal shows variation in time and space and certain sub-regions are projected to experience an increase in closed-low frequencies during certain seasons. A general increase in extreme rainfall events is projected over southern Africa despite the projected decrease in closed-low frequencies. It is deduced that this increase in extreme rainfall events is driven by intense convective rainfall events occurring within more frequently forming tropical-temperate cloud bands. Over Mozambique, extreme rainfall events are projected to increase in association with more frequently occurring closed-lows. Copyright © 2012 Royal Meteorological Society
... The expected Climate Change vulnerability of estuaries within each of the regions was based on available projected near-future and mid-future Climate Change projections for South Africa [37,[39][40][41][42][43][44]. These projections were derived using regional climate models and the Coordinated Regional Downscaling Experiment (CORDEX) of the World Climate Research Programme, largely based on outputs from the global climate model analysed in Assessment Report Five (AR5), including projections for low-mitigation (RCP8.5) ...
... One of the ways global warming manifests on land is through changes in rainfall patterns [14][15][16][17]45,[117][118][119]. For South Africa, there is strong evidence of statistically significant increases in rainfall over the southern interior regions [40,42], extending from the western interior of the Eastern Cape and eastern interior of the Western Cape northwards into the central interior region of the Northern Cape [57,120]. An increase in extreme rainfall events is projected to occur along the Southern Cape, Eastern Cape, and KwaZulu-Natal coasts during spring and summer, with a reduction in such events projected for winter and autumn (e.g., [40,42,121]). ...
... For South Africa, there is strong evidence of statistically significant increases in rainfall over the southern interior regions [40,42], extending from the western interior of the Eastern Cape and eastern interior of the Western Cape northwards into the central interior region of the Northern Cape [57,120]. An increase in extreme rainfall events is projected to occur along the Southern Cape, Eastern Cape, and KwaZulu-Natal coasts during spring and summer, with a reduction in such events projected for winter and autumn (e.g., [40,42,121]). This is associated with an upsurge in the frequency of occurrence of cut-off lows and more frequent occurrence of tropical-temperate cloud bands over the region [40,122]. ...
This review evaluates the vulnerability of South African estuaries to Climate Change in a data-limited environment. The regional-scale assessment is based on physical characteristics and predicted/measured changes in the abiotic drivers and ecosystem responses. The major Climate Change stressors were identified in order of importance as change in climatic and hydrological processes, ocean circulation and temperature regimes, sea level rise, increase in frequency and intensity of sea storms, and ocean acidification. Flow-related ecosystem responses included changes in mouth state, salinity regimes, biochemical regimes (nutrient fluxes), and floods and related sediment deposition/erosion cycles. The regional vulnerability assessment provides a summary of the key shifts scaled as high, medium, and low in estuary state. Changes in oceanic processes and temperature regimes drive shifts in nearshore temperatures of the transitional zones, with related ecological responses (e.g., range expansion). However, most structural and functional changes are expected along cool temperate and subtropical biogeographical regions, leading to notable shifts in mouth closures and salinity regimes, which in turn will affect estuary function and estuary-associated species. Monitoring and management of resources (e.g., fresh water and fisheries allocations) need to consider this in long-term planning.
... Several objective methods to identify synoptic weather systems using Numerical Weather Predication data have been developed and/or applied over SA. COLs have received special attention as Engelbrecht et al. (2015), Favre et al. (2013) and Singleton and Reason (2007) all defined circulation criteria to identify COLs over SA. Engelbrecht et al. (2013) identified closed mid-tropospheric lows but did not distinguish between cold and warm lows. Tropical weather systems have also received some attention as Malherbe et al. (2012) developed a method to identify westward moving tropical lows over the Mozambique Channel and Howard et al. (2019) used a tracking algorithm (TRACK) to identify Angola lows over sub-tropical SA. ...
... html was used to identify Africánes over December to March for each year between 1981 and 2020. Engelbrecht et al. (2013) stated that tropical low pressures have a horizontal scale of 500-1000 km and as the NCEP data set has a horizontal resolution of 2.5° (approximately 250 km), it makes it suitable to investigate synoptic scale weather systems (Engelbrecht et al. 2015;Favre et al. 2013;Malherbe et al. 2012;Singleton and Reason 2007). A landmask is used at the end of the identification process in order to identify Africánes only over the continent of Africa. ...
Large parts of southern Africa are influenced by extra-tropical weather systems for most of the year. During late summer (December–March), the circulation over the area becomes distinctly tropical. This paper introduces the Africáne, a synoptic scale tropical low-pressure system which has been shown to cause widespread and heavy rainfall over the southern sub-continent of Africa. The frequency of occurrence of Africánes, their contribution to rainfall and interannual variability are discussed in this paper. Africánes occur most frequently at the longitude of the Caprivi area with a second peak in frequency at around 32.5° E. They mostly occur over Namibia, Botswana and Zimbabwe and only infrequently infiltrate as far south as the borders of South Africa. However, when they do occur over South Africa, they cause widespread heavy rainfall and floods. Rainfall is mostly confined to the eastern flank of Africánes and between 20 and 35% of the annual rainfall over southern Africa in late summer can be attributed to these systems. There are two main synoptic regimes associated with Africánes: a westerly wave or tropical-temperature trough combines with the Africáne to pull rainfall southwards into South Africa. The second, is a mid-level subtropical high pressure, located south of the Africáne, which causes the rainfall to be confined to the north. The interannual variability of Africánes are closely linked to rainfall over southern Africa, such that an above normal number of Africánes in a season causes above normal rainfall over southern Africa. The number of Africánes that form per year is linked to El Niño–Southern Oscillation (ENSO). It is recommended that the predictability of Africánes on different time scales should be investigated.
... Most studies on COL simulations over the Western Cape have used global climate models (GCMs) or reanalysis datasets (Singleton and Reason 2007b;Favre et al. 2013). While resolution of the GCM simulations can resolve the spatial structure of COLs, it may not capture the influence of the Western Cape's complex topography (i.e., the mountains, coastlines, and sharp gradients between the warm Agulhas current and the cold Benguela current; Mahlalela et al. 2018) on COLs (Engelbrecht et al. 2013). For example, Abiodun et al. (2016) showed that the warm Agulhas current (the width of which is less than 100 km) plays a crucial role in the rainfall intensity of COLs. ...
... In the climatological fields (Fig. 7), the WRF and CFSR concur that the Western Cape is a hotspot for COL occurrences, although the frequency of the COLs over the Western Cape and surrounds is more pronounced in the simulation than in the reanalysis. This is in agreement with previous studies (e.g., Engelbrecht et al. 2013;Favre et al. 2013;Ndarana and Waugh 2010;Singleton and Reason 2007b). Given that COLs usually form from Rossby wave breaking, the hotspot in COLs over the Western Cape agrees well with the peak in Rossby wave breaking around the Western Cape (Ndarana and Waugh 2010). ...
Cut-off lows (COLs) cause hazardous weather but also play a crucial role in the annual rainfall of the Western Cape, especially during a drought year. However, there is a dearth of information on the capability of atmospheric models to reproduce the characteristics of COLs over this region. This study evaluates the capability of a regional climate model (WRF) in simulating COLs over the Western Cape, with emphasis on the drought periods. Observation, reanalysis and simulations datasets were analysed for the study. The simulated climatology and inter-annual variability of COL with the associated patterns were compared to the reanalysis and observation results. The Self Organising Map (SOM) was used to group the observed and simulated COL rainfall to similar patterns. The results of the analysis show that WRF captures the seasonal and annual climatology of COL and the associated rainfall, but the model struggles to simulate the inter-annual variability of the systems. The model reproduces all the COL rainfall patterns well, though it under-estimates the frequency of dry COLs. However, WRF simulation agrees with the reanalysis that wetter COLs over the Western Cape are associated with more transport of warm, moist air from the tropics. The results of the study have application in improving weather and seasonal forecasting of COLs over the Western Cape.
... Mid-latitude circulation patterns determine the tracks and intensities of such synoptic systems (and thus rainfall) across the region . Under future climate change scenarios, these circulation patterns are expected to change and impact regional rainfall regimes (Engelbrecht et al., 2013). A significant decrease in rainfall is projected for the southwestern Cape region, with more frequent prolonged dry periods (Engelbrecht et al., 2009;Engelbrecht et al., 2013;Mahlalela et al., 2018). ...
... Under future climate change scenarios, these circulation patterns are expected to change and impact regional rainfall regimes (Engelbrecht et al., 2013). A significant decrease in rainfall is projected for the southwestern Cape region, with more frequent prolonged dry periods (Engelbrecht et al., 2009;Engelbrecht et al., 2013;Mahlalela et al., 2018). This will have profound impacts on the local economy, which relies heavily on water provision from rainwater storage reservoirs. ...
Surface pressure observations are invaluable for meteorological investigations as they enable reconstructions of and insights to historical large‐scale tropospheric circulation. This article endeavours to use a daily reduced mean sea level pressure (MSLP) series to reconstruct the monthly frequency of cold fronts, associated with mid‐latitude cyclones, overpassing Cape Town (southwestern Cape region of South Africa) during the 19th century. Using modern (2011–2017) daily MSLP data and synoptic charts, the relationship between MSLP values and the probability of a cold front overpassing, is established and applied to historical (1834–1899) MSLP data. Although no significant trend in cold front frequency is measured, greater interannual variability is noted during the first half of the study period (1837–1867). Results indicate a link between lower (higher) cold front frequencies and El Niño (La Niña) events, although not statistically significant. Additionally, correlations between cold front frequency and the Southern Annular Mode (SAM) appear to be weak. Although not statistically robust, we also note an apparent 1–2 year lagged association between years with above (below) average numbers of sunspots and above (below) average numbers of cold fronts.
... An increase in extreme rainfall events is projected to occur along the southern and eastern coasts of South Africa during spring and summer (Engelbrecht et al., 2013). An increase in runoff also affects the nutrient load entering estuaries, with inflow being an important source of dissolved and particulate nutrients. ...
... 5.3.6.4 Drought Downscaled regional climate models project slightly drier conditions for the winter rainfall region of South Africa with an increase in inter-annual variability (Hewitson and Crane, 2006;Engelbrecht et al., 2009Engelbrecht et al., , 2013. This may result in a decrease in flows and in increase in flow variability (droughts) in estuaries along the west coast (James et al., 2013), with the west coast a 'hotspot' of hydrological change (Schulze et al., 2005). ...
The aims of this project were described in the original proposal document as follows:
a) To determine the extent of blue carbon ecosystems in South Africa and estimate
blue carbon storage using the IPCC assessment methods.
b) To quantify the loss of blue carbon habitats and associated ecosystem services.
c) To predict the responses of blue carbon ecosystems to climate change in the form of sea-level rise and increased global temperatures.
The following tasks were developed to achieve the project aims:
Assess the extent of blue carbon habitats and their associated ecosystem services in South Africa. Quantify changes in blue carbon habitats and ecosystem services over time. Directly quantify blue carbon storage in mangrove, salt marsh, and seagrass habitats at a representative study site. Compare carbon storage between mangrove and salt marsh habitats at the mangrove distributional range limit.
- Measure surface elevation change in mangrove and salt marsh habitats and relate this response to sea-level rise threats. Predict changes in mangrove distribution along the South African coastline in
response to rising temperatures and changes in precipitation regimes associated with climate change. Review the implications of climate change on salt marsh along the South African coastline. Determine the viability of a carbon offset mechanism for South Africa’s blue carbon
ecosystems.
... Ziervogel et al. (2014) indicated that in the past 5 decades the mean annual temperature of South Africa was approximately 1.5 times more than that of the global average and an increased in rainfall frequency was also observed. In addition to the latter, Engelbrecht et al. (2012) projected that South Africa interior temperatures increase by twice that of the global rate. Madzivhandila (2015) indicated that between 1997 and 2009, the country was 2% hotter and 6% drier. ...
... Daily maximum and minimum temperatures are increasing, and the number of hot days will continue to increase, more heat waves, droughts and floods, heavy storms and extreme weather events are expected to intensify (Ericksen, Ingram, & Liverman, 2009;Madzivhandila, 2015). It was reported that increased flooding could be experienced in areas that are expected to receive more rainfall and droughts and reduced water availability in areas with reduced rainfall (DEA, 2013a;Engelbrecht, Engelbrecht, & Dyson, 2012). ...
Understanding exposure, sensitivity, and adaptive capacities of a country is important for resilience building and policy discourses especially the pursuit of water security objectives. South Africa is characterized by a semi-arid climate and highly variable spatiotemporal precipitation patterns and high evapotranspiration rates. These constrain water resources availability negatively and impact economic development, livelihoods, and progress toward attainment of the Sustainable Development Goals (SDGs). This chapter presents a global overview of climate change scenarios in South Africa and their impact on water resources, water security, and governance, and offers suggestions for transitioning toward adaptive management in the water sector. We explore how South Africa can attain water security, the sector-wide challenges and opportunities and innovations in resilience building to climate change risks in the water sector. This chapter indicates both increase and reduction in water resource availability associated with climate change–related extreme events (floods and droughts) in different parts of South Africa. To reduce water insecurity appropriate legal and regulatory water resources framework of management are recommended. Adaptive water management strategies, such as use of smart water technologies, have the potential to increase the coping capacities to climate change related impacts.
... Very few seasonal or longer-period synoptic-scale studies of the drivers of extreme cold events in South Africa have been documented (Lengoasa, 1991). Cold weather and cold events are mainly produced by the occurrence of cold cut-off lows and the cold fronts of mid-latitudinal cyclones predominantly during winter (Engelbrecht et al., 2012;Abiodun et al., 2016;Lennard, 2019). Cold fronts are normally followed by a high-pressure systems over the Atlantic Ocean (Stander et al., 2016). ...
Extreme cold events (“cold waves”) have disastrous impacts on ecosystem and human health. Evidence shows that these events will still occur under current increasing mean temperatures. Little research has been done on extreme cold events, especially in developing countries such as South Africa. These events pose a significant threat due to the low adaptive capacity, urgent development needs and relatively inadequate infrastructure in South Africa. This study presents annual and seasonal, spatial and temporal trend analyses of extreme cold temperature events for the period 1960–2016. We apply the World Meteorological Organisation Commission for Climatology and Indices Expert Team on Sector‐Specific Climate Indices (ET‐SCI) to South Africa for the first time, with comparison to the World Meteorological Organisation Expert Team on Climate Change Detection (ETCCDI) indices previously used in South Africa. The extreme cold indices are calculated using the RClimDex and ClimPACT, respectively. Trends were calculated using the non‐parametric Mann‐Kendall test, Spearman Rank Correlation Coefficient and Sen's slope estimates. A decreasing trend is found for annual cold spell duration and cold wave frequency, at rates of 0.10 days.day⁻¹ and 0.02 events.day⁻¹, respectively. Seasonally, coldest day temperatures increased in autumn, with increases of 0.02°C.day⁻¹ for the period 1960–2016. Regionally, increasing trends in annual cold spell duration days were evident in stations located in the Western Cape, Eastern Cape, North‐West Province, at a rate of 0.03 days.day⁻¹. Increasing trends in cold waves were observed for stations in Northern Cape, Gauteng, KwaZulu‐Natal and the Eastern Cape Province, at a rate of 0.01 events.day⁻¹. These results contribute to the awareness and recognition of the incidence and duration of cold extreme events in South Africa, seeing that studies suggest that anomalously cold events may persist in a warming world.
... Despite the WC province's high-water vulnerability to drought impacts, only a limited number of climate projections studies have been made for the region (Engelbrecht et al. 2013;Abiodun et al. 2019). Hence, this primary purpose of the study was to examine the potential impacts of meteorological drought on water resource availability in the WC province, an area especially vulnerable to climate change. ...
Consistent drought modelling under plausible shared socioeconomic–representative concentration pathways (SSP–RCPs) are crucial for effectively managing future drought risk in agricultural environments. The Western Cape (WC) is one of South Africa’s main agro-based provinces and faces a mounting threat of water insecurity due to recurrent drought. The objective of this study was to predict meteorological drought hazard for 2021–2050 based on three CMIP6 scenarios: SSP5–8.5, SSP2–4.5 and SSP1–2.6. Precipitation simulations generated by the sixth version of Model for Interdisciplinary Research on Climate (MIROC6) under the SSP5–8.5, SSP2–4.5 and SSP1–2.6 scenarios were used from fifteen stations across the six AEZs of the WC province. The Standardised Precipitation Index (SPI) was computed at 12-month timescales. Trend analysis of precipitation datasets and the SPI-values were done at p < 0.05 using the Mann–Kendall (M–K) test. The findings revealed negative precipitation trends of − 7.6 mm/year in Ceres, while positive trends of 0.3 mm/year were observed in Malmesbury. These findings indicate an improvement from − 7.8 and − 6.4 mm/year in the same regions, respectively, compared to historical trends observed between 1980 and 2020. The results suggest that in 2042 and 2044, Bredasdorp will experience − 2 < SPI < − 1.5 under the SSP2–4.5 scenarios, while Matroosberg in 2038 under the SSP5–8.5 will experience SPI > − 2. The findings of this study will assist in the development of proactive planning and implementation of drought mitigation strategies and policies aimed at reducing water insecurity in AEZs.
... When an upper air trough becomes separated or 'cut-off' from the westerly wind regime, it is referred to as a 'cut-off low'. The generally slow-moving cut-off lows are responsible for many of the flood producing rains in South Africa, including the Eastern Cape (Engelbrecht et al. 2013;Engelbrecht et al. 2015). Their frequency peaks in March to May and September to November with lower frequency between December and February (IEA 2022). ...
As a percentage of the total global energy supply, wind energy facilities could provide 10% of the total global energy supply by 2050 as reported in IEA World Energy Outlook (2022). Considering this, a just transition to renewable and sustainable energy in South Africa is a genuine possibility if steps are taken immediately to achieve this. The Eastern Cape Province exhibits a strong wind resource which can be exploited towards expediting such a just energy transition. No research and related modelling have, to date, been undertaken in quantifying and relating the detailed P50 energy yield analyses of representative wind energy facilities in temporal and spatial dimensions to the occurrence of specific synoptic types in South Africa. To quantify this energy meteorology climatology for a suitably sized geospatial area in the Eastern Cape Province of South Africa (spatial focus area, latitude −30 to −35, longitude 20 to 30), the approach of using self-organising maps is proposed. These maps are used to identify the most common synoptic circulation types occurring in the Eastern Cape and can subsequently be mapped onto an equivalent time resolution wind energy production timeseries calculated based on probable wind energy facility sites. This paper describes comprehensive methodologies used to model the wind energy facilities, calculate with high confidence the P50 energy production, and then identify the predominant synoptic weather types responsible for the wind energy production in this spatial focus area. After quantifying the energy production, running a self-organising map software generates a purposely selected 35 node map that characterises archetypal synoptic patterns over the 10-year period. The synoptic types can be ranked by the highest energy production. It is shown that in this spatial area, monthly wind energy production is higher during the winter months. When the well-established high-pressure cells move northward, synoptic types associated with higher energy production are frequent and include tropical and temperate disturbances across South Africa, patterns resembling a ridging anticyclone off the west coast of South Africa and low-pressure cells occurring to the north and south. Low energy producing patterns show characteristics of the high-pressure cells moving southwards producing fine weather and mildly disturbed conditions. The purpose of this methodology is that it provides the foundation required to derive long-term frequency changes of these synoptic weather systems using global climate model ensembles and thus changes in wind energy production.
... Notwithstanding the inconsistencies across studies, most projections suggest that although the number of storm days will decrease (Hoegh-Guldberg et al., 2018;Roffe & Fitchett, 2020), daily rainfall will intensify (C. J. Engelbrecht et al., 2013;Pohl et al., 2017). This has repercussions for groundwater recharge and soil loss, with increased deep drainage, runoff and soil erosion and is a critical factor in determining flooding risk. ...
... Climate change is a significant concern in southern Africa, where the annual, terrestrial temperature increase is 1.1-1.5 times the observed global average of 0.65 °C, (Davis-Reddy & Vincent, 2017;Ziervogel et al., 2014). Unfortunately, it is difficult to monitor and link rainfall patterns to climate change due to its high spatial and year-to-year variability (Engelbrecht et al. 2013). However, there is a clear increase in the number of extreme climate events, for both temperature and rainfall, which includes frequent dry spells and daily rainfall intensity (Davis-Reddy & Vincent, 2017). ...
Large scale changes to the natural environment, due to both climate change and direct human activities (e.g., urbanization), pose a great risk to biodiversity. As this realization has set in, the number of studies modelling and monitoring the effect of environmental change on species response and survival has increased significantly; however, these studies focus on flagship species, often neglecting the lesser-known, cryptic species, which include the nocturnal primates. This is especially true for the 20 species of galago who, despite their large distribution throughout Africa, have had little to no research conducted on the effect of environmental change on population fitness and long-term survival. With urbanization set to increase throughout their distribution range, along with an increase in climate change parameters (e.g., increased temperature and a decrease in annual rainfall), the most studied species of the family, namely the African lesser bushbaby Galago moholi, provides an ideal model to assess the impact of future environmental change on galago species. In this review, we discuss the possible impact of environmental change on G. moholi and specifically focus on the effect of environmental change on feeding ecology, genetics, thermal biology, and reproduction, all of which contribute to the fitness and survival of the species. We also highlight the need for specific, long-term research to be conducted on the effect of environmental change on the survival likelihood of G. moholi and other galago species.
... Such extremes are likely to be more frequent and intense at and above 1.5 C global warming levels (Donat et al., 2016). Several studies have explored the response of rainfall extremes to climate change in South Africa (Engelbrecht et al., 2013;Mason et al., 1999;Mason & Joubert, 1997;Pinto et al., 2016;Shongwe et al., 2009). Pohl et al. (2017) pointed out a significant decrease in the number of rainy days and an increase in their intensity, in line with the Clausius-Clapeyron relation linking air moisture to temperature. ...
Extreme events contribute significantly to rainfall variability in semi‐arid regions like South Africa. Here, following the definition of a novel typology of rainfall extremes, disentangling large‐ and small‐scale events in Part I, we use quality‐controlled observational databases in South Africa, the ERA5 reanalysis and satellite estimates TRMM‐3B42 to examine the relationship between these two types of rainfall extremes and different modes of climate variability at various timescales. At low frequencies, rainfall extremes are assessed at interannual (IV: 2–8 years) and quasi‐decadal (QDV: 8–13 years) timescales, which are primarily associated with the El Niño–Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO), respectively. At subseasonal timescales, the typology of rainfall extremes is analysed depending on the synoptic configurations, as inferred by seven convective regimes including tropical temperate troughs (TTTs: 3–7 days), and the intraseasonal variability associated with the Madden–Julien Oscillation (MJO: 30–60 days). At the IV timescale, the occurrence of large‐scale extremes is substantially higher during its wet phases thereby suggesting a 400% rise in the occurrence of large‐scale extremes as compared to its dry phases. At the QDV timescale, variability mostly relates to the modulation of small‐scale extremes during its wet phases. Teleconnections with global sea surface temperature (SST) confirm that La Niña conditions favour overall wet conditions and extremes in South Africa. The numbers of large‐scale extremes are consistently related to warmer SSTs in the North Atlantic, while their link with warmer Indian and tropical South Atlantic oceans is found to be statistically independent of the state of ENSO. At the subseasonal timescales, large‐scale extremes largely occur during three out of the seven convective regimes identified in the southern African region whereas small‐scale extremes are nearly equiprobable during all convective regimes. The occurrence of large‐scale extremes during continent‐rooted TTT is further enhanced during the locally wet phases of the MJO and is symmetrically weakened during its dry phases.
... Hydrological models are widely employed to predict future stream runoff as a way to analyze climate change impacts on water resources. Several studies on the climate change impacts on hydrological processes have shown that, for instance, in southern Africa, there is a high likelihood of temperature increase in the future while precipitation and streamflow could increase or decrease depending on the region, the extent of catchment modification, and mostly the selected GCM/RCM type [87,145,155,156]. These studies have used either one or a combination of various hydrological models to simulate hydrological responses under different climate change scenarios. ...
Empirical evidence continues to show that climate change remains a threat to the stability of the hydrologic system. As the climate system interacts with the hydrologic cycle, one significant repercussion of global warming includes changes in water availability at both regional and local scales. Climate change adaptation is intrinsically difficult to attain due to the dynamic earth system and lack of a comprehensive understanding of future climate and its associated uncertainties. Mostly in developing countries, climate adaptation is hampered by scarcity of good quality and adequate hydro-meteorological data. This article provides a synopsis of the modelling chain applied to investigate the response of the hydrologic system under changing climate, which includes choosing the appropriate global climate models, downscaling techniques, emission scenarios, and the approach to be used in hydrologic modelling. The conventional criteria for choosing a suitable hydrological model are discussed. The advancement of emission scenarios including the latest Shared Socioeconomic Pathways and their role in climate modelling, impact assessment, and adaptation, are also highlighted. This paper also discusses the uncertainties associated with modelling the hydrological impacts of climate change and the plausible approaches for reducing such uncertainties. Among the outcomes of this review include highlights of studies on the commonly used hydrological models for assessing the impact of climate change particularly in the sub-Saharan Africa region and some specific reviews in southern Africa. Further, the reviews show that as human systems keep on dominating within the earth system in several ways, effective modelling should involve coupling earth and human systems models as these may truly represent the bidirectional feedback experienced in the modern world. The paper concludes that adequate hydro-meteorological data is key to having a robust model and effective climate adaptation measures, hence in poorly gauged basins use of artificial neural networks and satellite datasets have shown to be successful tools, including for model calibration and validation.
... The report warns that "climate change impacts are not to manifest only through changes in average temperature and rainfall patterns, but also through changes in the attributes of extreme weather events", such as floods. This was earlier also projected by Engelbrecht et al. (2013) who predicted, "more intense thunderstorms to occur more frequently over South Africa." ...
The devastation that excessive rainfall can cause is still fresh in our minds following the
recent floods in KwaZulu-Natal (KZN) and the Eastern Cape (EC). And if the first flood
was not devastating enough, the poor folks in those areas were surprised by a second heavy rain period a few weeks later, adding damage to infrastructure and suffering for inhabitants. Flooding can, as witnessed in these areas, significantly hinder economic opportunities, transportation of goods and services, as well as mobility and access to essential services, including health and education. One of the drivers blamed for the excessive rainfall is climate change. Climate change refers to long-term shifts in temperatures and weather patterns. According to the UN, “These shifts may be natural, such as through variations in the solar cycle. But since the 1800s, human activities have been the main driver of climate change, primarily due to burning fossil fuels
like coal, oil and gas.”
... which is commonly referred to as the low-mitigation scenario for the 21st century. The ability of CCAM-CABLE to simulate climate over Southern Africa has been showcased in several scientific outputs [59][60][61][62][63][64]. ...
The reliable performance of roads is crucial for service delivery, and it is a catalyst for
domestic and cross-border spatial development. Paved national roads are expected to carry higher traffic volumes over time as a result of urbanization and to support the economic development in the continent. Increased traffic levels combined with expected increases in air temperatures as a result of global warming highlight the need to appropriately select bituminous road materials for a reliable performance of asphalt roads. The objective of the paper is to present African case studies on the development of temperature maps necessary for performance-graded bitumen selection for road design and construction. A consistent approach, that caters for the variability of geographical,
environmental and climatic conditions, does not currently exist within the continent. Therefore, this paper discusses a series of critical components in the development of temperature maps for performance-graded bitumen including (i) pavement temperature models and climatic zones in Africa; (ii) the effect of urban heat islands on pavement temperature; (iii) sources of weather data and (iv) the mapping procedure to produce temperature maps. Characterizing the thermal properties of the pavement was found to be an important factor for reliably calculating expected road temperatures as well as the consideration of the ambient climate for a given location. During this study, the urban
heat island effect was found to have little influence on the maximum pavement temperatures but a significant effect on the minimum pavement temperatures. Some areas of the urban district assessed in this investigation were found to increase by two performance grades according to the minimum temperature criteria. The recent observed weather data from weather stations are the most accurate means of measurement of the ambient environmental conditions necessary for performance-based specifications, but they are not always easily accessible, and therefore other sources of data, such as
satellite data, may need to be used instead. With the expected temperature increases expected as a result of climate change, the use of Global Climate Models also opens new avenues for performance-based material selection in the African continent for expected climates as an alternative to traditional approaches based on historically observed weather.
... To better understand future climatic trends and extremes in SA, various Global Climate Models (GCMs) and Regional Climate Models (RCMs) have been used by, e.g. Maúre et al. (2018), Kalognomou et al. (2013), Shongwe et al. (2015), Dedekind et al. (2016), Archer et al. (2018), and Engelbrecht et al. (2013). Covering more of a decade of research, these projections have revealed a robust message of general drying being likely over SA under continued global warning. ...
This study evaluates precipitation trends in the upper Mzingwane sub-catchment (UMS) of Zimbabwe using ten World Meteorological Organization (WMO)’s Expert Team for Climate Change Detection Monitoring and Indices climate indices. Trend analysis for variables such as annual total precipitation, extremely wet days, consecutive wet and dry days is analysed. The UMS is of strategic socio-economic significance in terms of water security and sustenance to livelihoods in this region and the city of Bulawayo. The analysis is undertaken at four stations: Bulawayo Goetz, Filabusi, Mbalabala and Matopos National Park (MNP), for the period 1921–2000. In general, no statistically significant trends were detected for all indices in all stations (with the exception of MNP (in the westernmost extent of UMS)) which showed significant increasing (decreasing) trends for most dryness (total precipitation) extreme indices. This is indicative of persistent drying coupled with a shift towards shorter very wet periods with more intense precipitation in the past twentieth century. There is also an indication of a general north to south-western declining precipitation gradient during the past ~ 69 years over this region. These findings are not only useful in explaining the historical evolution of observed extremes and their associated socio-economic impacts but also present a baseline for comparative follow-up studies assessing the twenty-first century and future trends in precipitation extreme events in the UMS.
... Attempts by several studies on variability in precipitation climatology and extreme precipitation events across the globe and over different regions of West Africa have been well documented (e.g. Ogunjobi 2014, 2017;Chikezie et al. 2016;Dosio and Panitz 2016;Ekpoh and Nsa 2011;Engelbrecht et al. 2013, Engelbrecht 2015Gbode et al. 2019;Hulme et al. 2001;Malhi and Wright 2004;Nwosu et al. 2014;Ogunrayi et al. 2016;Oguntunde et al. 2011;Oguntunde and Abiodun 2013;Shongwe et al. 2009). Since the beginning of the twentieth century, total annual precipitation in Nigeria is found to have shown profound negative and positive trends over different time scales, i.e. decadal to long-term periods. ...
The purpose of this study is to assess spatial and temporal changes in extreme precipitation events from 1983 to 2017 over different climatic regions of Nigeria. Ground observations of daily precipitation in 17 meteorological stations scattered over the country were methodically analysed. Twelve widely used indices for the assessment of intensity (PRCPTOT, R × 5Days, SDII, R95p, R99p and R95pIndex) and frequency (CWD, CDD, R1mm, R10mm, R20mm and R25mm) of extreme precipitation were adopted. Linear trends were calculated using a least-square-fit approach, while significant trends were identified using the Mann–Kendall non-parametric test. Results revealed general significant (at p < 0.05) downward annual trends in precipitation intensity indices [i.e. total wet day precipitation, (PRCPTOT), daily precipitation (SDII), 5-day maximum precipitation, (R × 5Days), very wet (R95p) and extremely wet days (R99p)], particularly in the Savannah and Sahel regions. The frequency indices [i.e. consecutive dry days (CDD), wet days (R1mm), heavy (R10mm), very heavy (R20mm) and extremely heavy precipitation (R25mm)] increased significantly in the Sahel but decreased in other zones. We established that R1mm decreases with decreasing SDII, while CWD declines with reducing SDII and R95p in the entire country. The study further revealed that Sahel and Savannah zones are highly vulnerable to severe droughts with potential negative implications on food security and water resources. It concluded that recent changes in climate had significantly impacted the extreme precipitation events within and across different climatic regions of Nigeria.
... According to Fatti and Patel (2013), these affected areas are expected to experience more flooding in the future. Southern Africa is likely to show a pattern of increment in extreme rainfall especially in convective precipitation areas (Engelbrecht et al., 2012). Extreme rainfall in the study area causes river, urban, flash, and coastal floods (Davis, 2016). ...
Flood is known to be the leading cause of natural disasters globally leaving disastrous and devastating damages in its wake. Flood risk and their time of occurrence is usually difficult to monitor and predict without appropriate tools for continuous monitoring. Extreme and frequent rainfall is one of the major causes of flood disasters. Assessment of flood hazards and its subsequent analysis using the standardized precipitation index (SPI) is very effective in the prediction of flood risk with the strength of the SPI being the use of rainfall as the only input variable. The SPI is found to be valuable in prediction of meteorological and hydrological floods such as flash floods, groundwater floods and dam burst. The knowledge of the occurrence of these flooding events can be very beneficial in preventing extensive damages to property, infrastructure, agriculture, and loss of life. The aim of this study is to assess flood hazard in eThekwini metropolitan area by examining the trend of flood events from 1985 to 2016 by the use of the SPI and its potential to predict flood risk in the study area. The results show that SPI properly explains the development of the conditions leading up to the occurrence of floods events in the analyzed period. Thus, is indispensable in the assessment of flood risk leading to an accurate prediction. The knowledge of the pattern and trends obtained from the SPI analysis is valuable to decision‐makers for efficient flood risk management plans in the promotion of preventive actions for mitigating the impacts of floods.
... Climate alter is expected to have exceptional results on the African territory amid the 21st century with inadequate mitigation measures (Niang, Ruppei, Abdrabo, Essei, Lennard & Padgham, 2014). Warmth in Africa is anticipated to escalation fleetly to double the world heat rise (James & Washington, 2013;Engelbrecht, Engelbrecht & Dyson, 2013). Also, the Northern and the Southern part of Africa may likely end up drier beneath progressed anthropogenic production, as Eastern part of Africa and utmost risky humid Africa are hypothetical to come rainier (Christensen et al., 2007;Engelbrecht, McGregor & Engelbrecht, 2009;James & Washington, 2013;Niang et al., 2014). ...
Environmental change is the greatest threat to human life on the
planet in the twenty first century. Its miles a manner of unnatural weather
exchange, relatively because of ‘nursery gases’ as an after effect of human
interest. Agricultural sector is anticipated to be adversely impacted by
environmental change both in the present and in the future, thereby
negatively impacting means livelihood and food security. Agriculture
undoubtedly is a vital economic factor, and means of livelihoods in South
Africa. Because Climate change is expected to reduce crop yields in South
Africa, thus affecting food security and livelihood, adaptation strategies
need to be implemented to mitigate climate change effects. This paper gives
a detailed analysis and implications of environmental change effects on
agriculture sectors and significance for achieving growth results such as
food security, poverty alleviation, and sustainability in South Africa. Future
Prospects for South Africa show decreased rainfall, rising heat, and high
unpredictability for the better part of the area coupled with severe declines
on the drier and marginal western areas, hence it will affect food security. These consequences has great effects for
farming production in South Africa. As a result, South Africa is expected to see 10% to 50% reductions in
agricultural output, a situation that might increase food insecurity in the region. By perfecting knowledge through
educational institutions, knowledge will be raised concerning the impact of climate change and how to militate
against present and anticipated circumstances.
Keywords:– Adaptation, Agriculture, Climate change, Food security, Mitigation, South Africa
... Climate change is predicted to cause an increase in the frequency and intensity of extreme events such as droughts, sea storms and river floods along the southern African coastline (Engelbrecht et al. 2013, James et al. 2013). An increase in floods will increase sediment delivery to estuaries and associated intertidal habitats, e.g. ...
This chapter provides an overview of the main drivers of change in estuarine systems, their expected causes and impacts on estuarine fish and fisheries. An analysis of global, regional and local patterns of estuarine fish and how climate‐induced change may impact estuarine systems and their fish communities is provided. We also examine the main environmental, climatic and biological stressors likely to impact estuarine fish and associated fisheries. A set of case studies is used to illustrate the differences in potential impacts associated with various global regions and types of estuaries. An understanding of climate change in estuaries will support estuarine ecosystem resilience, inform management and facilitate adaptation.
... Thus, carbon emissions, environmental change, the shift of biological systems, ecological corruption, and the random condition have been expanding making the climate of any region inadmissible for human home (Ameen and Mourshed 2017;Zheng et al. 2019). Moreover, researchers predict that climate change and its consequences will increase every year, droughts will increase in intensity and frequency due to changes in rainfall, and temperatures will rise by 1.5 to 2 times the global temperature increase rate (Barros and Field 2014; Engelbrecht et al. 2013). A thorough understanding of vegetation dynamics, both spatially and temporally, might help reverse the situation and mitigate the effects and losses already experienced in impacted areas, alleviating the suffering of the vulnerable people. ...
Understanding the effects of vegetative land cover in Bangladesh on climatic variability and dynamics is still a critical issue for environmental sustainability as well as global and regional climate policy formulation. This study aimed to gain a better understanding of the responses of vegetation changes and built-up area changes to climatic variability in Bangladesh during 1990–2020. Based on the Normalized Difference Vegetation Index (NDVI) dataset, we analyzed the spatiotemporal characteristics of vegetation dynamics and the proportion of urban land changes across all the urban and rural areas of Bangladesh and investigated the relationships between the variability of temperature, precipitation, and humidity through Pearson’s correlation (PC) and geographically weighted regression (GWR) models. This study found complex variations in growing-season NDVI and climatic factors across the country. The results indicate a declination of vegetation areas and precipitation, with an increase in built-up areas (12.60% in urban and 11.68% in rural areas), temperature, and humidity. The correlation between growing-season NDVI and climatic factors demonstrates a strong inverse influence of temperature up to − 0.78; and positive influences of rainfall up to + 0.51 and humidity up to + 0.06, but in the case of built-up area changes, temperature change is positively correlated, while rainfall and humidity are negatively correlated to built-up expansion. Findings suggest that climatic factors are more responsive to built-up land expansion than vegetation dynamics in the urban and rural areas of Bangladesh. The unplanned development activities would persist and continue to affect the environment and sustainability. This study provides policymakers and the Bangladesh government with critical information on environmental development and sustainability improvements that will lead to the long-term sustainability of natural resources and environmental health.
... Most predictions of future climate change agree that Africa's climate will get warmer, but there is a high degree of uncertainty regarding future changes in rainfall. While it is commonly expected that warmer climates bring higher rainfall due to increased ocean evaporation, this is not always the case, and some areas are expected to experience aridification and/or increased extreme events (Engelbrecht et al. 2013;Pinto et al. 2018). This is of critical importance to areas where agriculture is rain fed and already marginal (Pohl et al. 2017). ...
... Most predictions of future climate change agree that Africa's climate will get warmer, but there is a high degree of uncertainty regarding future changes in rainfall. While it is commonly expected that warmer climates bring higher rainfall due to increased ocean evaporation, this is not always the case, and some areas are expected to experience aridification and/or increased extreme events (Engelbrecht et al. 2013;Pinto et al. 2018). This is of critical importance to areas where agriculture is rain fed and already marginal (Pohl et al. 2017). ...
... There have been some studies that have produced downscaled climate projections over Namibia (Dirkx et al. 2008;Turpie et al. 2010;Coetzee 2010;Engelbrecht et al. 2013;GRN 2015). A study by Davis (2011) downscaled six GCMs for the period 2036-2065 showing that Namibia would likely experience a decrease in annual rainfall totals and an increase in temperatures by 1.2°C in the south west to 2.8°C in the north east (averaged across the simulations). ...
... The intensity of daily rain has increased in recent years over southern Africa, most significantly during extreme rainfall days and periods (New et al., 2006;Roy and Rouault 2013;MacKellar et al., 2014;Kruger and Nxumalo, 2017). Extreme rainfall events have become more frequent (Rapolaki et al., 2019) and are projected to persist over the sub-continent in the future climate due to an increase in concentration of anthropogenic greenhouse gases (Engelbrecht et al., 2013;Kendon et al., 2019). More importantly, sub-daily rainfall extremes are projected to become more severe than daily extremes over southern Africa by 2100, under the RCP8.5 scenario in a convection-permitting 4.5-km CP4A model (Kendon et al., 2019). ...
An extreme sub-daily precipitation event produced about 300 mm of rainfall in less than 4 hours overnight from 13-14 February 2019 resulting in high floods in Thohoyandou, a small town northeast of South Africa. We employed station, radar, satellite and reanalysis datasets to investigate the rainfall, circulation and thermodynamic fields and understand the meteorological structure of the extreme event via a multiscale analysis. The large-scale synoptic environment was characterized by a mid-tropospheric tropical-temperate trough and attendant cloud band coupled to a surface high ridging over the southeast coast of the country. We found that whilst heavy rainfall (>50 mm/24 hr) was widespread ahead of the upper trough, extreme amounts (∼100 mm/hr) were localized due to a cloudburst. A small perturbation to the favorable large scale mid-tropospheric environment also contributed to localized heavy rainfall. The south-north pressure gradient was steepened by a surface low over southern Mozambique resulting in enhanced moisture flux convergence deriving from the southwest Indian Ocean. The interaction of prevailing surface winds and a low-level jet with the steep topography of the adjacent Soutpansberg Mountain Range enhanced low-level convergence and lifting in the area. We also show that the highest rainfalls were uphill of the location of flooding which was contained in a poorly drained valley. Whereas the Unified Model forecasts appeared accurate for the large-scale pattern of heavy rainfall in the area, the rainfall peak was generally underestimated, whilst the timing of extreme rainfall was delayed in the 18Z simulation, which is used by forecasters operationally. Our findings contribute to understanding the occurrence of extreme weather events over northeastern South Africa and also how models treat them, towards natural disaster risk reduction.
... Although no single weather event can be confidently attributed to climate change, an increasing number of studies are documenting a positive trend of severe weather events in southern Africa (Davis-Reddy and Vincent, 2017;Kruger and Nxumalo, 2017). These include an increase in the frequency of extreme rainfall events associated with land-falling tropical cyclones and severe thunderstorms, particularly in the eastern parts of southern Africa and south of South Africa (Malherbe et al., 2013;Engelbrecht et al., 2013). ...
On 11 December 2017, a tornadic supercell initiated and moved through the northern Highveld region of South Africa for 7 h. A tornado from this supercell led to extensive damage to infrastructure and caused injury to and displacement of over 1000 people in Vaal Marina, a town located in the extreme south of the Gauteng Province. In this study we conducted an analysis in order to understand the conditions that led to the severity of this supercell, including the formation of a tornado. The dynamics and thermodynamics of two configurations of the Unified Model (UM) were also analysed to assess their performance in predicting this tornadic supercell. It was found that this supercell initiated as part of a cluster of multicellular thunderstorms over a dry line, with three ingredients being important in strengthening and maintaining it for 7 h: significant surface to mid-level vertical shear, an abundance of low-level warm moisture influx from the tropics and Mozambique Channel, and steep mid-level lapse rates. It was also found that the 4.4 km grid spacing configuration of the model (SA4.4) performed better than the 1.5 km grid spacing version. SA1.5 underestimated the low-level warm moisture advection and convergence , and missed the storm initiation. SA4.4 captured the supercell; however, the mid-level vorticity was found to be 1 order of magnitude smaller than that of a typical mesocyclone. A grid length of 4.4 km is too coarse to fully capture the details of a mesocyclone, which may also explain why the model underestimated the surface to mid-level wind shear and low-level horizontal mass and moisture flux convergence. Future investigations will involve experimental research over the Highveld region of South Africa to understand mesoscale and local dynamics processes responsible for tornadogenesis in some severe storms. Such a study, to the best of our knowledge, has never been conducted.
... The issues of concern are the frequency of occurrences of extreme climatic events that have been projected for South Africa (e.g. [56,196]) and because of data limitations, these models cannot adequately project. Thus, crop simulation models require detailed soil input parameters (soil depth, soil chemical composition, and soil physical characteristic) associated with processes that limit crop growth under water scarcity conditions or enhance yields under wet conditions. ...
A broad scope of crop models with varying demands on data inputs is being used for several purposes, such as possible adaptation strategies to control climate change impacts on future crop production, management decisions, and adaptation policies. A constant challenge to crop model simulation, especially for future crop performance projections and impact studies under varied conditions, is the unavailability of reliable historical data for model calibrations. In some cases, available input data may not be in the quantity and quality needed to drive most crop models. Even when a suitable choice of a crop simulation model is selected, data limitations hamper some of the models’ effective role for projections. To date, no review has looked at factors inhibiting the effective use of crop simulation models and complementary sources for input data in South Africa. This review looked at the barriers to crop simulation, relevant sources from which input data for crop models can be sourced, and proposed a framework for collecting input data. Results showed that barriers to effective simulations exist because, in most instances, the input data, like climate, soil, farm management practices, and cultivar characteristics, were generally incomplete, poor in quality, and not easily accessible or usable. We advocate a hybrid approach for obtaining input data for model calibration and validation. Recommended methods depending on the intended outputs and end use of model results include remote sensing, field, and greenhouse experiments, secondary data, engaging with farmers to model actual on-farm conditions. Thus, employing more than one method of data collection for input data for models can reduce the challenges faced by crop modellers due to the unavailability of data. The future of modelling depends on the goodness and availability of the input data, the readiness of modellers to cooperate on modularity and standardization, and potential user groups’ ability to communicate.
... Southern Africa is also predicted to receive less rainfall overall [27,28]. In addition, regional climate models forecast a higher incidence of concentrated and extreme rainfall events [29,30]. All these predictions are dire for households that are already vulnerable. ...
In this paper, household vulnerability in Limpopo National Park (LNP) is discussed in relation to interannual climate variability and the effects of the park itself. Climate variability is high and projected to increase with climate change. Meanwhile, the establishment of the national park in 2002 has added both challenges and possibilities. We present the results of livelihood surveys carried out 2013 and discuss changes taking place in and around the park until present day. Constraints and possibilities for endurability of households are discussed. In conclusion, the vulnerability of the LNP households to climate change is high, but there are a number of strategies in place to ensure endurability. Migrant labour is vital for household economy, and cattle production is important for endurability. The hunting ban in the park and losses of crops and livestock due to wildlife present serious challenges. Income from the illegal wildlife trade, which exploded from 2011, has had little impact on household economy or in mitigating household vulnerability but has had devastating effects on the social fabric of households. We discuss possible avenues for transformability, where access to markets and transport remain a challenge for farmers. Individual cattle owners’ view of constraints and possibilities for expanding cattle herding are discussed and assessed in terms of transformability.
... Sustainability 2021, 13, 1234 ...
Understanding the impacts of climate variability and change on terrestrial ecosystems in Africa remains a critical issue for ecology as well as for regional and global climate policy making. However, acquiring this knowledge can be useful for future predictions towards improved governance for sustainable development. In this study, we analyzed the spatial–temporal characteristics of vegetation greenness, and identified the possible relationships with climatic factors and vulnerable plant species across Africa. Using a set of robust statistical metrics on the Normalized Difference Vegetation Index (NDVI3g) for precipitation and temperature over 34 years from 1982 to 2015, relevant results were obtained. The findings show that, for NDVI, the annual rate of increase (0.013 y−1) was less than that of decrease (−0.014 y−1). In contrast, climate data showed a sharper increase than a marked decrease. Temperature is increasing while rainfall is decreasing, both at a sharp rate in central Africa. In Africa, tree cover, broadleaved, deciduous, closed to open (>15%) and shrubland plant species are critically endangered. The tropical vegetation devastated by the climate variability, causes different plant species to gradually perish; some were cleared out from the areas which experienced degradation, while others were from that of improvement. This study provides valuable information to African governments in order to improve environmental sustainability and development that will lead to the sustainability of natural resources.
... Very few seasonal or longer-period synoptic-scale studies of the drivers of extreme cold events in South Africa have been documented (Lengoasa, 1991). Cold weather and cold events are mainly produced by the occurrence of cold cut-off lows and the cold fronts of mid-latitudinal cyclones predominantly during winter (Engelbrecht et al., 2012;Abiodun et al., 2016;Lennard, 2019). Cold fronts are normally followed by a high-pressure systems over the Atlantic Ocean (Stander et al., 2016). ...
Extreme cold events ('cold waves’) have disastrous impacts on ecosystem and human health. Evidence shows that these events will still occur under current increasing mean temperatures. Little research has been done on extreme cold events, especially in developing countries such as South Africa. These events pose a significant threat due to the low adaptive capacity, urgent development needs and relatively inadequate infrastructure in South Africa. This study presents annual and seasonal, spatial and temporal trend analyses of extreme cold temperature events for the period 1960‐2016. We apply the World Meteorological Organisation Commission for Climatology and Indices Expert Team on Sector‐Specific Climate Indices (ET‐SCI) to South Africa for the first time, with comparison to the World Meteorological Organisation Expert Team on Climate Change Detection (ETCCDI) indices previously used in South Africa . The extreme cold indices are calculated using the RClimDex and ClimPACT, respectively. Trends were calculated using the non‐parametric Mann‐Kendall test, Spearman Rank Correlation Coefficient and Sen's slope estimates. A decreasing trend is found for annual cold spell duration and cold wave frequency, at rates of 0.10 days.y‐1 and 0.02 events.y‐1, respectively. Seasonally, coldest day temperatures increased in autumn, with increases of 0.02°C.y‐1 for the period 1960‐2016. Regionally, increasing trends in annual cold spell duration days were evident in stations located in the Western Cape, Eastern Cape, North‐West Province, at a rate of 0.03 days.y‐1. Increasing trends in cold waves were observed for stations in Northern Cape, Gauteng, KwaZulu‐Natal and the Eastern Cape Province, at a rate of 0.01 events.y‐1. These results contribute to the awareness and recognition of the incidence and duration of cold extreme events in South Africa, seeing that studies suggest that anomalously cold events may persist in a warming world.
... Previously, the CCAM downscalings have been shown to realistically represent present-day climate over southern Africa (e.g. Engelbrecht et al., 2009Engelbrecht et al., , 2013Engelbrecht et al., , 2015. ...
Anthropogenic climate change is expected to impact ecosystem structure, biodiversity and ecosystem services in Africa profoundly. We used the adaptive Dynamic Global Vegetation Model (aDGVM), which was originally developed and tested for Africa, to quantify sources of uncertainties in simulated African potential natural vegetation towards the end of the 21st century. We forced the aDGVM with regionally downscaled high‐resolution climate scenarios based on an ensemble of six general circulation models (GCMs) under two representative concentration pathways (RCPs 4.5 and 8.5). Our study assessed the direct effects of climate change and elevated CO2 on vegetation change and its plant‐physiological drivers. Total increase in carbon in aboveground biomass in Africa until the end of the century was between 18% to 43% (RCP4.5) and 37% to 61% (RCP8.5) and was associated with woody encroachment into grasslands and increased woody cover in savannas. When direct effects of CO2 on plants were omitted, woody encroachment was muted and carbon in aboveground vegetation changed between –8 to 11% (RCP 4.5) and –22 to –6% (RCP8.5). Simulated biome changes lacked consistent large‐scale geographical patterns of change across scenarios. In Ethiopia and the Sahara/Sahel transition zone, the biome changes forecast by the aDGVM were consistent across GCMs and RCPs. Direct effects from elevated CO2 were associated with substantial increases in water use efficiency, primarily driven by photosynthesis enhancement, which may relieve soil moisture limitations to plant productivity. At the ecosystem level, interactions between fire and woody plant demography further promoted woody encroachment. We conclude that substantial future biome changes due to climate and CO2 changes are likely across Africa. Because of the large uncertainties in future projections, adaptation strategies must be highly flexible. Focused research on CO2 effects, and improved model representations of these effects will be necessary to reduce these uncertainties. Climate change and elevated CO2 are expected to drive vegetation changes in Africa. We used an ensemble of dynamic vegetation model simulations to assess the impacts of these drivers on carbon stocks and biomes until 2099. Climate change and elevated CO2 led to an 18% to 61% increase in carbon stocks, which was primarily driven by CO2 fertilization. Associated biome changes are likely across Africa, especially changes from savanna to forest. Disabling CO2 fertilization resulted in a −22% to +11% change in carbons stocks. These large uncertainties in future projections imply that adaptation strategies need to be flexible.
... The LULC changes and their associated impacts on water yield variations in the basin were investigated under the effect of climate variability. It is believed that climate variability due to rising in surface temperature, fluctuations in rainfall patterns, and an increase in frequency and intensity of drought conditions (Engelbrecht et al., 2013;Gebremeskel Haile et al., 2019;Midgley & Bond, 2015;Niang et al., 2014) could all affect the hydrological characteristics of basins and surface runoff (Guzha et al., 2018). Thus, there is an urgent need for assessing the status of the available land and water resources in its holistic approach to properly manage and plan hydrological ecosystem services in the basin as well as other catchments in the Horn of Africa. ...
Climate variability and drought are increasing in the Horn of Africa. Evaluating land use/land cover (LULC) changes and their impacts on water availability and variation are vital for regional land use planning and water resources management. LULC changes during 2000–2015 were estimated using high‐resolution Landsat images and the Google Earth Engine cloud platform, and land use dynamic index (K). The impact of LULC change on water yield was evaluated using the Integrated Valuation of Ecosystem Services and Tradeoff (InVEST) model. The results at a regional scale show that there were rapid decreases in the area of forests and barren lands (‐K) while there was a drastic increase in the built‐up area (+K values). The transition was found to occur from forested land to low and very low biomass areas with 51.13% and 16.7%, respectively. There were similar LULC changes in the Mereb‐Gash River Basin. The mean annual water yield increased for all the catchments during 2000–2015 and with the peak in 2005. The highest annual sum water yield decreased in the forested lands from 43.18 million m³ in 2000 to 4.1 million m³ in 2015. There was a strong positive correlation between areal changes (%) and the annual water yield variations (%) for all the LULC types except for water body, and the correlation was significantly positive for forest (p < 0.01). The study demonstrates that the decrease in forested areas and expansion in the built‐up areas had large impacts on water yield. The impacts may increase pressure on ecosystem services, exacerbate water scarcity, and food insecurity.
... Most of the agricultural production in South Africa is rainfed which means that farmers rely on rainfall to grow crops and produce marketable yields, and climate projections suggest that there will be serious threats to agricultural production affecting both commercial and smallholder farmers (Tadross et al. 2005;Schulze 2007;Davis 2011;Engelbrecht et al. 2013). Climate projections indicate that South Africa will likely experience moderate decreases of rainfall and higher inter-annual variability, increased probability of drought events, increase in minimum and maximum temperatures, and a decrease of water availability due to the changes in land-use towards industrial and urban usage (Meadows 2006;Ruane et al. 2015a). ...
Agriculture in South Africa sustains about 70% of the region’s population for food, income and employment, playing an important role for food security and the local economy. The focus of the study was the commercial maize farms of the Free State Province given their importance in the National economy. The Regional Integrated Assessment (phase I) was implemented to assess climate change and adaptation that links climate, crops, economic data and tools developed by the Agricultural Model Intercomparison and Improvement Project (AgMIP). In this context, the “system” is defined as a whole of agronomic and socio-economic factors. Within that framework three core questions were being evaluated: (i) Impacts of climate change under current system; (ii) Impacts of climate change under future system; (iii) The role of adaptation under climate change and the future system. Maize production will decrease between 10% to 16% as a result of projected climate impacts. Also, current agricultural production systems are negatively affected by climate change with an increase in poverty rates between 2% to 3%. The projected adoption of the adapted technology would result in positive increased net returns and a decrease in poverty rate of between 12% and 22%. The results of this study show that implementing adaptation measures, including strategies indicated by the local stakeholders, will have positive impacts on the agricultural production systems and can contribute to support and inform climate change policy decision making such as the development of National Adaptation Plans.
Climate change and its impact on environment is become the hot topic in the world. Bangladesh is a highly populated developing and agro-based economic country. Impact of several climatic factors such as rainfall, air temperature, humidity on agriculture is immense. But changes found in the trend of these climatic factors in here. This research aimed to detect the trend of three climatic factors, rainfall, temperature, and humidity over last 42 years (1981–2022) and along this, to explore the relation between vegetation coverage and climatic factors. The entire analysis is conducted for Upazilla level in Bangladesh. Maan-Kendal Test and Sen slope estimation is followed to detect the trend of three climatic factors and multiple regression model, Geographically Weighted Regression (GWR) Model and Ordinary Least Square (OLS) Regression Model is applied to explore the relationship between vegetation coverage and climatic factors. Positive trend is found for rainfall (24–147 mm/year) and humidity (0.16% − 0.47%) but negative trend is detected for temperature (− 0.03 to 0.00 ℃) for some Upazilla in Bangladesh. By GWR model, ranges of very weak to weak influence of vegetation coverage on the climatic factors are found for most of the Upazilla in Bangladesh. From the results of OLS, very strong correlation is found between the change rate of vegetation coverage and climatic factors for most of the Upazilla in Bangladesh especially the Upazilla of Sylhet and Chittagong Division. As Upazilla Master Plan is initiated in Bangladesh for each Upazilla, the outcomes of this research will help the policy makers to take the suitable plan for environment as well as agricultural development for each Upazilla through which sustainable development can be ensured.
Africa is a rich continent in natural heritage, but it is facing numerous environmental challenges that are expected to worsen due to the impact of climate change. The Intergovernmental Panel on Climate Change has identified Africa as the region most vulnerable to the impacts of climate change, making it crucial to understand and address the current and future impacts of this phenomenon in the region.
This chapter provides a comprehensive analysis of the current and projected impacts of climate change in the five subregions of Africa: Northern Africa, West Africa, Central Africa, East Africa, and Southern Africa. Each of these subregions faces unique climate challenges and is expected to experience rising temperatures, reductions in precipitation, and an increase in the frequency of heat waves (HWs).
Northern Africa is expected to see a strong increase in temperatures and a decrease in precipitation, resulting in drier conditions. In East Africa, the projected impacts of climate change include higher annual mean temperatures, more frequent hot extremes, and heat waves. Central Africa is expected to experience an average temperature increase of 0.6–2.1 °C, along with an increase in hot days and extreme heat wave events. West Africa is likely to face increased meteorological droughts, increased wind speed, and changes in monsoon precipitation. Southern Africa is expected to warm faster than the global average, with semiarid and drier areas being particularly vulnerable to the impacts of climate change.
In conclusion, this chapter underscores the critical importance of addressing the impacts of climate change in Africa to mitigate its environmental and human impacts.
Southern Africa relies heavily on precipitation for agricultural purposes; therefore, spatial and temporal changes in precipitation are crucial to identify and understand. The South Indian Ocean Convergence Zone (SIOCZ), a large-scale, austral summer rainfall feature extending across southern Africa into the southwest Indian Ocean, is evaluated in future projections. Using a best-fit algorithm, future projections of the SIOCZ are determined, which indicate a northward shift of approximately 120 km in CMIP5 models under RCP8.5. A dipole pattern of precipitation wetting/drying is evident, where wetting occurs to the north of the climatological axis of maximum rainfall, implying a northward shift of the Inter Tropical Convergence Zone, consistent with the SIOCZ shift. Common drivers responsible for model changes include enhanced warming in the northern Indian Ocean in line with the ‘warmest-get-wetter’ sea surface temperature hypothesis, which impacts circulation by transporting moisture away from the SIOCZ towards the equator. Most CMIP5 models exhibit drying trends over the SIOCZ region, with mechanisms driving uncertainty related to diverse warming trends across models. Empirical orthogonal function patterns of future precipitation changes across CMIP5 models exhibit a pattern much like the SIOCZ, which is related to inter-model changes in future temperature changes. Reductions in model spread are established in SIOCZ projections, whereby model processes of change exhibit agreement, despite differing initial SIOCZ conditions. Therefore, model process convergence and coherence are established with respect to projected changes in the SIOCZ, irrespective of initial climatology biases. Understanding future changes in this feature will help inform decision-making for water and agriculture adaptation planning in southern Africa.
Phuthaditjhaba is situated at the foothills of the Maloti-Drakensberg, one of southern Africa’s primary water-producing regions. Nevertheless, the region suffers from a recurring lack of sufficient water for domestic and agricultural use. Since 2015, this chronic water crisis has created a state of conflict between the inhabitants of the region and the local government. Against the backdrop of the United Nations’ Sustainable Development Goals, this paper provides a commentary on the contrasting realities of this town nestled within one of South Africa’s most biodiverse regions, yet lacking in the very resource for which it is supposedly famous. We identify both gross mismanagement and neglect by local municipal authorities and climate change as compounding factors leading to the recurring lack of sufficient good quality water in the region. These are some of the major threats to sustainable development in Phuthaditjhaba, which may exacerbate poverty and escalate social tensions that often burst into spontaneous social unrest in the town and its surroundings.
Many areas in South Africa are prone to localized flooding. With climate change already said to affect the intensity of rainfall, there is a need to investigate if there is a change in the probability of significant to extreme daily rainfall across South Africa. This was investigated through the analysis of the daily time series of 70 manual rainfall stations, over the period 1921 to 2020. The analysis period was divided into two equal periods of 50 years for comparison. With the application of the gamma distribution, it is shown that most stations experienced an increase in the probability of receiving more than 50 mm per day, defined as significant rainfall, in the latter half of the analysis period. Also, most stations showed an increase in their 1:50- and 1:100-year return period values, with some stations over the eastern parts showing increases of over 100 mm. There was also an increase in the probability of “heavy rainfall” (>75 mm) and “very heavy rainfall” events (>115 mm) between the first and second half of the analysis period for most stations over the country when applying the Peak-Over-Threshold approach. In summary, the results indicate that, although the number of rain days has remained near-constant over the 1921–2020 period, the probability of experiencing significant and extreme daily rainfall events has increased generally for most regions in South Africa. This is of concern as rainfall of this nature can have serious consequences in terms of flooding, erosion, and damage to agriculture and infrastructure.
Synopsis-Performance grade specifications for bituminous binders focus on the evaluation of bitumen properties based on the loading and environmental conditions under which the material will be subjected to in the field. The temperature of the asphalt layer (as determined by the climate and geographical location), in conjunction with the grade and age of the bitumen, plays a pivotal role in determining the stiffness or dynamic modulus of the asphalt layer. Most climate models predict an increasing rate in the rise of average air temperatures in the near future. As the average air temperatures increase, it is expected that the frequency and duration of extreme temperatures will also rise. This will have a direct impact on asphalt pavement performance by increasing the potential for permanent deformation of pavements and the rate of age hardening of asphalt binders. In this study, interpolated maps of minimum and maximum pavement temperatures were generated using a climate model for predicted air temperatures for two 20-year periods, up to the years 2040 and 2060. The same model was used to generate two historic 20-year periods, going back to 2000 and 1980. The Viljoen temperature prediction algorithms were used for calculating the pavement temperatures as opposed to the Superpave models. The maps produced in this paper can eventually be used to identify adaptation measures which may include modifying current design and maintenance practices.
Africa is one of the most vulnerable continents to climate change (CC), warming at ‘double the global average rate’. The southern African region is already a CC hotspot with climate variability exposing stark societal and biophysical ecosystem vulnerabilities. South African and southern African youth are beginning to claim their place at various CC negotiation tables adding to the voices of government and various civil society groups. In this paper, written by a group of youth activists, civil society organisation leaders, educators and climate scientists, we track the journey that a group of young change-makers and local government officials (in the age range 15–24) have taken in securing a seat at the policy table. The challenges, caveats and course corrections that have been taken in the Johannesburg Youth Climate Action Plan (YCAP) process and the wider country, are interrogated. This YCAP Johannesburg experiment provides a useful learning exercise for subsequent CC policy and practice engagements in the country and elsewhere.
Rainfall extremes are of major and increasing importance in semi‐arid countries and their variability has strong implications for water resource and climate impacts on the local societies and environment. Here, we examine intraseasonal descriptors (ISDs) and wet extremes in austral summer rainfall (November–February) over South Africa (SA). Using daily observations from 225 rain gauges and ERA5 reanalysis between 1979 and 2015, we propose a novel typology of wet extreme events based on their spatial fraction, thus differentiating large‐ and small‐scale extremes. Long‐term variability of both types of extreme rainfall events is then extensively discussed in the context of ISDs. The results demonstrate that using 7% of spatial fraction simultaneously exceeding the local threshold of the 90th percentile produces remarkable results in characterizing rainfall extremes into large‐ and small‐scale extremes. Austral summer total rainfall is found to be primarily shaped by large‐scale extremes which constitute more than half of the rainfall amount under observation, and nearly half in ERA5. Observation (ERA5) shows an average of 8 ± 5 (20 ± 7) days per season associated with large‐scale extremes, which are comprised in 5 ± 3 (10 ± 3) spells with an average persistence of at least 2 days. Overall, we find a strong dependence of total rainfall on the number of wet days and wet spells that are associated with large‐scale extremes. We also find that large‐ and small‐scale extremes are well‐organized and spatially coherent in nature yet extreme conditions during small‐scale events are found sporadic over the region, contrasting with large‐scale events for which extreme conditions are found over a larger and coherent region.
Increasing extreme climate events and cyclonic activities provide clear evidence that the Southern African Development Community (SADC) region is a hotspot for climate change-driven natural disasters which critically disrupt agricultural production cycles. This is especially true with regard to the production of cereal, produce widely used to represent food security. Although studies have attempted to disentangle the effect of demand vis à vis projected population growth on cereal production across the region, the contradiction between cereal production and climate disaster preparedness remains poorly resolved. Therefore, literature on the subject matter is scanty. The present study is motivated by the need to overcome this paucity of literature and thus, deepen our understanding of cereal production and climate disaster preparedness in the region. Therefore, the main aim of this study is to assess public institutional support structures that are currently being employed for climate disaster preparedness in the cereal value chain across Zambia as perceived by small scale farmers. After a comprehensive assessment of focus group discussions (FGDs), several points emerge specifically highlighting four salient findings: first, results show that a government-led Farmer Input Support Programme (FISP) is the only strategy particularly targeted at disaster preparedness. All other initiatives are targeted at improving or safeguarding livelihoods with some components having a ripple effect on the cereal value chain. Second, results show that climate forecasts that are supposed to trigger early action are generally characterized by low prediction skill with more false alarms and misses than hits. Third, forecasts were found to lack geographical specificity with generalities over large areas being common thus, diminishing their usefulness at the local scale. Fourth, end-users found forecasts to usually contain technical jargon that is difficult to decipher especially that most small-scale farmers are illiterate. This study concludes that to fully support the cereal value chain and realize food security in Zambia, policy formulation that champion the establishment of an effective early warning and early action system (EWEAS) involving multiple interest groups and actors should be considered a matter of urgency.
This paper provides a systematic review of studies assessing the impact of climate change on crop yields in southern Africa. Moreover, it synthesises the current knowledge of the impact of elevated ambient CO2 levels (eCO2) and temperatures on physiological processes, and the application of this knowledge in mechanistic crop models. While eCO2 evidently has a strong impact on photosynthesis and crop water use, it is uncertain how this will work out for the climatic and crop management conditions prevailing in southern Africa. The impact of heat stress on crop reproductive processes and the process of transpiration cooling mitigating heat stress are poorly represented in models, while both process are relevant given the climatic conditions prevailing in southern Africa. Twenty studies assessing the impact of climate change on future yields of crops, mostly maize, have been retrieved. The results suggest that potato, Bambara groundnut and sugarcane yields may improve. No consistent trends for maize and sorghum could be identified. While yield predictions are obviously context-specific, large uncertainties related to climate predictions and crop models imply results should be treated with caution. Suggestions are made for field experimentation and the improved application of crop models for climate change research in the region.
This study evaluates precipitation trends in the upper Mzingwane sub-catchment (UMS) of Zimbabwe for the variables of annual precipitation, extremely wet days, consecutive wet days and consecutive dry days. The UMS is of strategic socio-economic significance in terms of its provision of water security and sustenance to livelihoods. The analysis is undertaken at four stations: Bulawayo Goetz, Filabusi, Mbalabala and Matopos National Park, and for the period 1921–2000. In general trends were found not to have local statistical significance, with the exception of the Matopos station (in the westernmost extent of UMS) which records significant increasing (declining) trends for most dryness (wetness) extreme indices. A general north to south-western declining precipitation gradient during the past ~ 69 years over the UMS was also found. The findings provide a baseline for future extended historical and future precipitation trend studies, and are important in the context of the socio-economic impacts of extreme events in this region.
The effects of climate change on water resources could be numerous and widespread, affecting water quality and water security across the globe. Variations in rainfall erosivity and temporal patterns, along with changes in biomass and land use, are some of the impacts climate change is projected to have on soil erosion. Sedimentation of watercourses and reservoirs, especially in water-stressed regions such as sub-Saharan Africa, may hamper climate change resilience. Modelling sediment yield under various climate change scenarios is vital to develop mitigation strategies which offset the negative effects of erosion and ensure infrastructure remains sustainable under future climate change. This study investigated the relative change in sediment yield with projected climate change using the Soil and Water Assessment Tool (SWAT) for a rural catchment in South Africa for the period 2015–2100. Data from six downscaled Coupled Global Climate Models (CGCM) were divided into three shorter time periods, namely, 2015–2034, 2045–2064 and 2081–2100. Results were then compared with a control scenario using observed data for the period 2002–2017. The results show that, if
left unmanaged, climate change will likely lead to greater sediment yield, of up to 10% more per annum. Peak sediment yield will also increase almost three-fold throughout the century. The study shows that projected climate change will have multiple negative effects on soil erosion and emphasised the need for changes in climate to be considered when embarking on water resource developments.
The effects of climate change on water resources could be numerous and widespread, affecting water quality and water security across the globe. Variations in rainfall erosivity and temporal patterns, along with changes in biomass and land use, are some of the impacts climate change is projected to have on soil erosion. Sedimentation of watercourses and reservoirs, especially in water-stressed regions such as sub-Saharan Africa, may hamper climate change resilience. Modelling sediment yield under various climate change scenarios is vital to develop mitigation strategies which offset the negative effects of erosion and ensure infrastructure remains sustainable under future climate change. This study investigated the relative change in sediment yield with projected climate change using the Soil and Water Assessment Tool (SWAT) for a rural catchment in South Africa for the period 2015–2100. Data from six downscaled Coupled Global Climate Models (CGCM) were divided into three shorter time periods, namely, 2015–2034, 2045–2064 and 2081–2100. Results were then compared with a control scenario using observed data for the period 2002–2017. The results show that, if left unmanaged, climate change will likely lead to greater sediment yield, of up to 10% more per annum. Peak sediment yield will also increase almost three-fold throughout the century. The study shows that projected climate change will have multiple negative effects on soil erosion and emphasised the need for changes in climate to be considered when embarking on water resource developments.
Savannas are dynamic and heterogeneous environments with highly variable vegetation that responds to a multitude of interacting drivers. Rainfall, soils, herbivory, fire and land use all effect land cover in savannas. In addition, savannas have a long history of human use. Setting management goals is therefore complex. Understanding long-term variability in savannas using palaeoecology provides a context for interpretation of recent changes in vegetation and can help to inform management based on acceptable or historical ranges of variability. In this article, we review and synthesise palaeoecological data from southern African savannas and use resilience theory as a framework for structuring and understanding of vegetation dynamics in savannas. We identify thresholds between alternate stable states, which have different ecological properties, suites of species and ecosystem services. Multi-proxy palaeoecological records can assist in identifying alternate states in savanna vegetation, as well as showing how different drivers (fire, herbivory, nutrients and climate) interact to drive transitions between states.
Conservation implications: The ecological thresholds identified from palaeoecological data can be used to inform the development of management thresholds, known as thresholds of potential concern. Thresholds of potential concern are designed to facilitate or impede transitions between states by manipulation of those variables (e.g. fire and herbivory) that can be controlled at the landscape scale.
The possible impacts of extreme events on the ecology of selected aquatic biota within the Mbhashe Estuary were investigated during a four year (2010–2013) spring sampling programme. During periods of low to average flow conditions the estuary is shallow, turbid and characterised by the presence of fluid mud and the build-up of mud and clay deposits. During these conditions, extremely high biomasses of intertidal microalgae and zooplankton are present. Fish and macroinvertebrate abundance and diversity are also highest during low-flow conditions. Flood events can reset, or partially disrupt, the sediment erosion/depositional cycle and decrease the biomass and diversity of plankton, fish and macroinvertebrate species. The Mbhashe Estuary’s unique fluid mud habitat is
therefore subjected to regular resetting, which potentially contributes to the fluid nature of the muds. A storm surge in 2011 resulted in the temporary dieback of an area of mangroves, as a result of the deposition of marine sediment. Although extreme events seem to play an important role in the deposition and erosion cycle of the estuary, an increased frequency of both types of extreme events may ultimately result in estuarine habitat loss, which will adversely affect the biota of the estuary.
Daily rainfall over the Gauteng Province, South Africa, was analysed for the summer months of October to March using 32-yr (1977 to 2009) daily rainfall data from about 70 South African Weather Service stations. The monthly and seasonal variation of heavy rainfall occurrences was also analysed. Three 24-h heavy rainfall classes are defined considering the area-average rainfall. A significant rainfall event is defined when the average rainfall exceeds 10 mm, a heavy rainfall event when the average rainfall exceeds 15 mm and a very heavy rainfall event when the average rainfall exceeds 25 mm. January months have the highest monthly average rainfall as well as the highest number of heavy and very heavy rainfall days. The month with the second-highest number of heavy and very heavy rainfall days is February followed by March and October. December has the second-highest monthly average rainfall and the most days with rain. However, it is also the month with the lowest number of heavy and very heavy rainfall days. The highest 24-h rainfall recorded at a single station during the 32-yr period was 300 mm in December 2006. However, rainfall exceeding 115 mm at a single rainfall station in the Gauteng Province is very rare and does not occur every year. January months receive these events more than any other month but this only transpires in approximately a third of years. The central and north-western parts of the Province experience the most events where the rainfall at a single station surpasses 75 and 115 mm. With regard to seasonal rainfall, the 1995/96 summer rainfall season had the highest seasonal rainfall during this 32-yr period followed by the 1999/2000 season. The 1995/96 season had above normal rainfall in both early and late summer but the 1999/2000 season was dry in early summer and very wet in late summer. Significantly high seasonal rainfall is associated with above-normal rainfall in late summer.
The SPI is an index that allows monitoring the intensity and spatial extension of droughts in South Africa at different time scales. The SPI is linked to the probability occurrence of dry or wet event at different time scale (3,6 12 and 24 months). The SPI allow monitoring operationally any location with a 30-year time series and is used in that paper to do a retrospective analysis of droughts and wet period in South Africa since 1922. According to this index, the 8 most severe droughts at the 6 months scale for the 80 districts of the summer rainfall region of South Africa happened in 1926, 1933, 1945, 1949, 1952, 1970, 1983, 1992. During all those years an El Niño event happened in the Pacific. Likely most wet seasons are found at the same time of a La Niña event. There are a mean number of 16 dry (SPI1) districts per year in South Africa. There is considerable decadal variability and an 18-20 year cycle is found in the number of dry district for the summer rainfall region. Drought lasting 3 years are not uncommon for each of the 8 South African homogeneous rainfall region defined by the South African Weather Service. There is a significant increase in the total number of dry and wet districts per decade since the 70's.
Two regional climate models (RCMs) are used to downscale 10 years of control and 10 years of future (2070–2079) southern African climate, as simulated by the HadAM3 general circulation model forced with the A2 SRES emissions scenario. Changes in early and late summer season total rainfall, rain days and average surface temperature are presented for the projected future climate. The two RCMs indicate broadly consistent changes over the region as a whole. However, time- and location-dependent differences are apparent, especially in the simulated magnitude of change, due to different representations of each model's internal physics and local hydrological cycle.
NCEP/NCAR reanalysis data is used widely in the atmospheric sciences. Although these data are generated using homogenous techniques, the effect of changes in the atmospheric observing system is unavoidable. One prominent impact is the introduction of satellite data in 1978, particularly over the southern hemisphere where conventional observations are sparse. This paper attempts to quantify the extent to which the introduction of satellite data impacts both daily and inter-annual scales of variability, using a Self-Organizing Map (SOM) analysis technique. It is clear that daily circulation statistics are quite different before and after 1979, and are generally more typical of model climatology before 1979. Inter-annual variability also appears to be reduced before 1979 in the mid-latitudes of the southern hemisphere. These caveats need to be borne in mind when performing studies over the southern hemisphere pre-1979.
February-March 2000 saw devastating floods in Mozambique, Zimbabwe, and South Africa. Due to the huge damage and loss of life, global media attention was extensive. Less well known is that one of the weather systems that contributed to these floods (ex-Tropical Cyclone Eline) tracked almost 2000 km across southern Africa toward the cool southeast Atlantic and led to substantial rainfall over arid to semiarid southern Namibia (over two standard deviations above average for these two months and the wettest summer since 1976). Less than 5% of southwest Indian Ocean tropical cyclones actually make landfall on the east coast of southern Africa and even fewer significantly penetrate into the interior, because of the relatively dry 1-1.5-km-high interior plateau that covers most of the region. It is argued that the precursor synoptic conditions together with large-scale circulation and SST anomalies over the Indian Ocean associated with a strengthening La Niña were highly favorable for this unusual evolution and track of Eline. A summary of the accuracy of La Réunion and Met Office forecasts of Tropical Cyclone Eline over the Indian Ocean is given. Over the mainland, almost all countries do not have any NWP capacity, and the challenges and potential solutions for improved forecasting for the region are discussed. It is argued that by keeping informed of current rainfall, vegetation, and soil moisture conditions over southern Africa, as well as evolving climate signals in the tropical oceans, local forecasters could at least be in a state of heightened alert in advance, since these factors significantly influence extreme weather event characteristics in the region.
The ability of the CSIRO-9 General Circulation Model (GCM) to capture surface cutoff lows over eastern Australia is investigated by comparing composites of ten GCM cases with ten observed lows. The lows are also studied individually to compare their development and movement, as well as synoptic features, which may have been smoothed out in the compositing process. Finally, the incidence of all such lows in the 1×C02 and 2×C02 simulations are examined to determine the possible effects a doubling of C02 will have on their occurrence.The GCM surface lows were found to develop from an upper-level cutoff low in a manner similar to the observed lows. In both sets, this development took place between the upper-level subtropical and polar jets in all seasons except summer, where only one jet was evident. Latent heat release appeared to play an important role in the intensification of the surface lows. The main difference between the two sets of cutoff lows was that the GCM surface lows tended to develop farther to the east of the upper-level cutoff, the upper-level features were less intense and occlusion did not take place. As a result, the GCM lows had a greater eastward translation compared to the observed lows, which often meander along the east coast for several days while they intensify. These features appear to be related to the low resolution of the GCM.The frequency of east Australian cutoff lows was underpredicted in the WM by about 45% in the 1×C02 simulation, with the greatest underprediction occurring in autumn and winter. Analysis of upper-level jet structure indicated that the GCM produced a poor simulation of the dual jet structure aloft, which may account for this problem. The 2×C02 simulation produced even fewer cutoff lows over eastern Australia. This was probably caused by the reduced baroclinicity due to increased warming of polar regions, which resulted in an even weaker dual jet structure. The cast Australian cutoff lows were found to be more intense in the 2×C02 Simulation, suggesting the greater role played by latent heat effects once development has been initiated.
An objective routine for identifying the individual cyclones has been developed. The procedure was designed with the aim to keep the input expenditure low. The method ensures a complete collection of cyclones and an exclusion of short time fluctuations attributed to numerical effects. The cyclones are identified as relative minima of the geopotential height field in 1000 hPa. The initial stages of the cyclones are found by locating relative maxima in the 850-hPa vorticity field. Further on the temporal development of the extrema is taken into consideration. An individual cyclone is regarded only if it exists for at least 24 h and if it attains a mature stage at least once, where a certain margin of the geopotential gradient to the surroundings is exceeded. The identification routine is applied to simulations with the Hamburg general circulation model ECHAM in T21 resolution. Also, cyclone tracks based on ECMWF analyses are evaluated, to which the model results are compared. The effect of different climate conditions, for example, global warming, on cyclone frequency and track location is investigated. It is found that a warmer SST distribution leads to a slight reduction of cyclone frequency in the Southern Hemisphere in fall (March, April, May) and winter (June, July, August); elsewhere the differences are not significant. 25 refs., 9 figs., 1 tab.
Methods used for the solution of hydrodynamic governing equations in
numerical models of the atmosphere are discussed. In particular grid
point finite difference methods and problems and methods used for time
and horizontal space differencing are covered. Specific problems
relating to the numerical solution of the advection and gravity wave
equations are discussed.
Variability in the characteristics of cut-off low pressure systems over subtropical southern Africa is examined for the 1973–2002 period. These characteristics include their seasonality, frequency, duration, location and size. It is found that on average 11 cut-off lows occur over southern Africa south of 20°S per year and are most common in the March-May season. Potential relationships between the number of cut-off lows over southern Africa with the El Niño Southern Oscillation (ENSO), the Pacific South America pattern, the wave number 3 pattern and the semi-annual oscillation (SAO) are discussed. La Niña years appear to be associated with above average annual frequencies of cut-off lows but the reverse is generally not true for El Niño years. There was a shift in the preferred season for cut-off lows from March–May to June–August in the 1980s, which coincided with a weakening of the SAO and a shift in zonal wave number 3. This period also showed a change in the preferred location of these systems from southwestern subtropical southern Africa to the northeast of the region. The results suggest that there may be a relationship between cut-off lows over subtropical southern Africa, the wave number 3 pattern in the Southern Hemisphere and the SAO. Copyright © 2006 Royal Meteorological Society.
The standardised precipitation index (SPI) is an index that allows monitoring the intensity and spatial extension of droughts at different time scales (3, 6, 12 and 24 months). The SPI is linked to the probability occurrence of dry or wet events. The SPI allows monitoring operationally any location with a 30-year time series. It is also used here to do a retrospective analysis of the spatial extension and intensity of droughts in South Africa since 1921. According to this index, the 8 most severe droughts at the 6-month time scale for the summer rainfall region of South Africa happened in 1926, 1933, 1945, 1949, 1952, 1970, 1983 and 1992. There is considerable decadal variability and an 18 to 20 year cycle is only found in the number of dry districts. The total number of wet and dry districts per decade seems to have increased since the 1960s. Drought lasting 3 years is not uncommon for each of the 8 South African rainfall regions defined by the South African Weather Service. Combining the retrospective analysis with real time monitoring could be extremely beneficial in the development of response, mitigation strategies and awareness plans.
Rainfall variability and changes in Southern Africa over the 20th century areexamined and their potential links to the global warming discussed. After a shortreview of the main conclusions of various experiments with Global AtmosphericModels (GCM) forced by increased concentrations of greenhouse gases for SouthernAfrica, a study of various datasets documents the observed changes in rainfall featuresat both daily and seasonal time steps through the last century. Investigations of dailyrainfall parameters are so far limited to South Africa. They show that some regionshave experienced a shift toward more extreme rainfall events in recent decades.Investigations of cumulative rainfall anomalies over the summer season do notshow any trend to drier or moister conditions during the century. However, closeexamination reveals that rainfall variability in Southern Africa has experiencedsignificant modifications, especially in the recent decades. Interannual variabilityhas increased since the late 1960s. In particular, droughts became more intense andwidespread. More significantly, teleconnection patterns associated with SouthernAfrican rainfall variability changed from regional before the 70s to near global after,and an increased statistical association to the El Nio – Southern Oscillation (ENSO) phenomenon is observed. Numerical experiments with a French GCM indicate that these changes in teleconnections could be related to long-term variations in the Sea-Surface-Temperature background, which are part of the observed global warming signal.
The NCEP and NCAR are cooperating in a project (denoted "reanalysis") to produce a 40-year record of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involves the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data; quality controlling and assimilating these data with a data assimilation system that is kept unchanged over the reanalysis period 1957-96. This eliminates perceived climate jumps associated with changes in the data assimilation system. The NCEP/NCAR 40-yr reanalysis uses a frozen state-of-the-art global data assimilation system and a database as complete as possible. The data assimilation and the model used are identical to the global system implemented opera- tionally at the NCEP on 11 January 1995, except that the horizontal resolution is T62 (about 210 km). The database has been enhanced with many sources of observations not available in real time for operations, provided by different coun- tries and organizations. The system has been designed with advanced quality control and monitoring components, and can produce 1 mon of reanalysis per day on a Cray YMPI8 supercomputer. Different types of output archives are being created to satisfy different user needs, including a "quick look" CD-ROM (one per year) with six tropospheric and stratospheric fields available twice daily, as well as surface, top-of-the-atmosphere, and isentropic fields. Reanalysis information and selected output is also available on-line via the Internet (http//:nic.fb4.noaa.gov:8000). A special CD- ROM, containing 13 years of selected observed, daily, monthly, and climatological data from the NCEP/NCAR Re- analysis, is included with this issue. Output variables are classified into four classes, depending on the degree to which they are influenced by the observations andlor the model. For example, "C" variables (such as precipitation and surface fluxes) are completely determined by the model during the data assimilation and should be used with caution. Never- theless, a comparison of these variables with observations and with several climatologies shows that they generally contain considerable useful information. Eight-day forecasts, produced every 5 days, should be useful for predictabil- ity studies and for monitoring the quality of the observing systems. The 40 years of reanalysis (1957-96) should be completed in early 1997. A continuation into the future through an identical Climate Data Assimilation System will allow researchers to reliably compare recent anomalies with those in earlier decades. Since changes in the observing systems will inevitably produce perceived changes in the climate, par- allel reanalyses (at least 1 year long) will be generated for the periods immediately after the introduction of new ob- serving systems, such as new types of satellite data. NCEP plans currently call for an updated reanalysis using a state-of-the-art system every five years or so. The suc- cessive reanalyses will be greatly facilitated by the generation of the comprehensive database in the present reanalysis.
The intense precipitation event over East London, South Africa, on 15–16 August 2002 is investigated using a mesoscale model (MM5) and its sensitivity to sea surface temperature (SST) and topography tested. Over 300 mm of rain fell in 24 h over East London as compared to the August average of 78 mm. The intense precipitation resulted from a cut-off low system aloft and the formation of a low-level jet (LLJ) near the surface. The MM5 control simulation indicated that the intense precipitation was due to the ascent of moist air at the leading edge of the LLJ, which advected warm moist air at low levels onto the coastal mountains and was enhanced by the formation of a meso-beta scale low-pressure system just off the coast. The ascent at the leading edge of the LLJ formed the ascending arm of a convective circulation cell. Sensitivity experiments with MM5 indicated that the warm core of the Agulhas Current contributed to the formation of the meso-beta scale low, while the mesoscale structure of the SST field was important in determining its location and that of the LLJ, and therefore the precipitation in the model. Most of the moisture originated from the Agulhas Current region. The South African topography was found to influence the location of the LLJ via trapping a near-surface warm trough on the eastern side of the Drakensberg mountains. We suggest that deficiencies in the control experiment may have been due to inaccuracies in using a weekly mean SST field to force the model at the lower boundary.
Climatic change in southern Africa over the last two millennia will be reviewed. Atmospheric processes and circulation changes modulating recent climatic change in the region will be considered. Present-day drought conditions will be modelled from sea-surface temperature variations. Finally, the most up-to-date general circulation model simulations of possible future equilibrium and transient changes of climate over southern Africa arising out of greenhouse warming over the next 50 years or so will be presented. -Author
Flood-producing rainfall over central South Africa during February and March 1988 was the result of two distinctive circulation systems embedded in an environment suitable for intense convection. The spatial structure, development and movement of the disturbances that produced the flood rains are difficult to analyse with conventional surface-based meteorological observations. Satellite observations and high-quality numerical weather-model analyses are useful in studying these events, as is illustrated here. Meteosat water-vapour images, satellite microwave sensor-derived precipitable water and marine windspeed data, and European Centre for Medium-range Weather Forecasts (ECMWF) model analyses of relative humidity and wind components are combined with synoptic analyses in providing a comprehensive view of the flood disturbances and the large-scale environment in which they occurred. -from Authors
The current state of regional climate and climate change modelling using GCMs is reviewed for southern Africa, and several approaches to regional climate change prediction which have been applied to southern Africa are assessed. Confidence in projected regional changes is based on the ability of a range of models to simulate present regional climate, and is greatest where intermodel consensus in terms of the nature of projected changes is highest. Both equilibrium and transient climate change projections for southern Africa are considered. Warming projected over southern Africa is within the range of globally averaged estimates. Uncertainties associated with the parameterization of convection ensure that projected changes in rainfall at GCM grid scales remain unreliable. However, empirical downscaling approaches produce rainfall changes consistent with synoptic-scale circulation. Both downscaling and grid-scale approaches indicate a 10-15% decrease in summer rainfall over the central interior which may have important implications for surface hydrology. Climate change may be manifested as a change in variability, and not in mean climate. Over southern Africa, increases in the variability and intensity of daily rainfall events are indicated.
The southern African region is susceptible to climatic extremes and particularly to extended dry periods. Possible changes in the probability of dry years under doubled-CO2 conditions are examined using output from the CSIRO nine-level general circulation model. Changes in annual mean rainfall are not expected to be significant. However, the model simulates an increase in the probability of dry years in the tropics, to the south-west of the subcontinent, as well as over the western and eastern parts of South Africa and southern Mozambique, where large percentage increases in the most intense dry spells are indicated. A decrease in the frequency of dry years is simulated over much of the interior of the subcontinent south of 10°S. In regions where the frequency of dry years decreases, the most severe events occur less often. The CSIRO nine-level model indicates a shift in the frequency distribution of daily rainfall events under doubled-CO2 conditions. A small change in the frequency distribution of daily rainfall events may have further implications for the frequency of mid-summer droughts during the peak summer rainfall period of December-February. Increases in the frequency of mid-summer droughts are simulated over the eastern part of the subcontinent south of 20°S.
The quality of cyclone tracks associated with model output of various resolutions is determined using a high- resolution dataset (1.125 83 1.1258, 2 h) mapped to different spatial (triangular truncations, T21, T42, T63, T84) and temporal resolutions (4 h, 6 h, 12 h, 18 h, 24 h). Three sets of comparisons are performed to study the impact of increasing (i) temporal, (ii) spatial, and (iii) spatiotemporal resolutions (T21/24 h, T42/12 h, T63/6 h, T84/4 h). The different ''test'' resolutions are compared with a ''perfect'' reference dataset of optimal res- olution. A general method to quantitatively compare two sets of tracks is developed. For a given test dataset, this method yields the ratio of perfect tracks (which are also identified in the reference set) and the ratio of missing tracks (present in the reference set, but missing in the test set). In 24-h data (T42) only about 45% of the cyclones can be identified with cyclones in 2-h data (73% in 12 h, 85% in 6 h).
The projected climate‐change signal in simulations by the Conformal‐Cubic Atmospheric Model (CCAM) over southern Africa is presented, with particular emphasis on the projected changes in circulation over the region. Current (1975–2005) and future (2070–2100; A2 scenario) climate simulations are used for this purpose.
In the austral winter of the future climate, frontal rain bands are displaced to the south as a result of the subtropical high‐pressure belt intensifying to the south of the subcontinent. In spring and autumn, mid‐ and upper‐level highs are simulated to become more prominent over the eastern and central parts of southern Africa. The enhanced subsidence associated with these systems results in generally lower rainfall totals over much of the south‐eastern subcontinent. To the north of these highs, enhanced westward moisture advection contributes to increased rainfall totals over northern Mozambique, whilst along the western periphery of the anomalously strong highs, enhanced southward moisture advection results in higher rainfall totals over Namibia, Botswana and the central and western interior of South Africa. In mid‐summer, the Indian Ocean High (IOH) is simulated to intensify most over the south‐western Indian Ocean (IO). This seemingly results in the more frequent occurrence of the cloud bands that constitute the South Indian Convergence Zone (SICZ) over the south‐eastern subcontinent—resulting in generally wetter conditions over this region. Copyright © 2008 Royal Meteorological Society
The study provides perspective on the contribution of landfalling tropical systems (cyclones, depressions, storms and lows) from the southwest Indian Ocean (SWIO) towards rainfall over the eastern interior of southern Africa, over the period 1948–2008. Although these systems contribute to <10% of the annual rainfall occurring over the region, their relative contribution to local and widespread heavy rainfall events is shown to be highly significant. About 50% of widespread heavy rainfall events over northeastern South Africa are caused by landfalling tropical systems. Fourier analysis performed on the time series of rainfall occurring over northeastern South Africa in association with these systems reveals the existence of a quasi-18-year cycle. The cycle coincides with the well-known quasi-18-year Dyer–Tyson cycle in rainfall over the summer rainfall region of South Africa. These results suggest that atmospheric and surface conditions leading to wet phases of the Dyer–Tyson cycle also favour the landfall and subsequent westward movement of tropical systems from the SWIO over southern Africa – and their eventual contribution to rainfall over northeastern South Africa and southern Zimbabwe. Copyright 2011 Royal Meteorological Society
The intense precipitation event over East London, South Africa, on 15–16 August 2002 is investigated using a mesoscale model (MM5) and its sensitivity to sea surface temperature (SST) and topography tested. Over 300 mm of rain fell in 24 h over East London as compared to the August average of 78 mm. The intense precipitation resulted from a cut-off low system aloft and the formation of a low-level jet (LLJ) near the surface.The MM5 control simulation indicated that the intense precipitation was due to the ascent of moist air at the leading edge of the LLJ, which advected warm moist air at low levels onto the coastal mountains and was enhanced by the formation of a meso-beta scale low-pressure system just off the coast. The ascent at the leading edge of the LLJ formed the ascending arm of a convective circulation cell.Sensitivity experiments with MM5 indicated that the warm core of the Agulhas Current contributed to the formation of the meso-beta scale low, while the mesoscale structure of the SST field was important in determining its location and that of the LLJ, and therefore the precipitation in the model. Most of the moisture originated from the Agulhas Current region. The South African topography was found to influence the location of the LLJ via trapping a near-surface warm trough on the eastern side of the Drakensberg mountains. We suggest that deficiencies in the control experiment may have been due to inaccuracies in using a weekly mean SST field to force the model at the lower boundary.
This study evaluates differences in the precipitation regime over southeastern Africa simulated by two global climate models under present (1961–1990) and future (2071–2100) conditions as a result of greenhouse gases anthropogenic forcing. In particular, the characteristics of precipitation episodes with duration of some days are compared in both simulations. Precipitation in the models is previously compared to precipitation data obtained from the ERA-40 reanalyses and the Climate Prediction Centre (CPC), Climate Prediction Merged Analysis of Precipitation (CMAP). A precipitation episode is defined here as a period with a minimum number of consecutive days with daily precipitation above a threshold amount.
We consider a great range of episodes according to the preset threshold number of days (1–15 days) and daily precipitation amount (1–15 mm/day). For both climates, the number of episodes, their average duration and intensity are compared. The analysis is performed for both models. The results clearly show a tendency for a decrease in the number of episodes, in most of the region and for most episode categories, due to anthropogenic climate change. The duration of the episodes is reduced in the future climate for weak episode categories. For mild to intense episodes their duration is expected to increase over a small part of the region. The intensity of all episode categories is increased practically over the whole region. The spatial structure of these changes and its distribution according to the episode category are documented in this study. Copyright
A general circulation model simulation is used to investigate possible changes in rainfall over southern Africa resulting from a doubling of atmospheric carbon dioxide. Simulated increases in rainfall intensity are found to be a spatially coherent and an apparently less regionally dependent signal of climatic change than changes in annual means or number of rain-days. Accordingly, increases in both the frequency and intensity of extreme daily rainfall events are simulated throughout most of the subcontinent. Simulated increases in the intensity of the lowest frequency floods are shown to be particularly severe, suggesting that greenhouse-relate d climatic change may be most detectable through an increase in extreme flood events rather than changes in long-term means. Similar results are evident when changes in the frequency and intensity of prolonged rainfall events, measured over a period of five consecutive days, are analysed. All results are qualitatively similar to those for the Australian region, except that the model's sensitivity to sharp changes in topography over southern Africa is highlighted. © 1997 by the Royal Meteorological Society.
South Africa forms the southern end of Africa with its northern boundary at approximately 22°S and the southern-most point, Cape Agulhas, at approximately 35°S. During most of the year atmospheric circulation over South Africa, especially the central and southern regions, is dominated by extra tropical weather systems such as cut-off lows, cold fronts and the ridging Atlantic Ocean High. Weather forecasters in South Africa are trained on and experienced in forecasting rainfall from these systems. During late summer weather systems from the tropics invade the northern regions of South Africa. Because tropical weather systems only appear during three or four months of the year weather forecasters often lack the experience to identify them timeously. Invading tropical weather systems are often associated with heavy rainfall and flooding (February 1988, February 1996, February 2000). It is very important that forecasters identify these tropical systems and apply appropriate forecasting techniques. Prior to this research no objective system to classify tropical systems and to pinpoint areas of significant to heavy rainfall was employed locally. This research resulted in the model for the identification of tropical weather systems (MITS). MITS has five components based on the atmospheric dynamics important for the development of convective rainfall from tropical systems. The application of MITS is detailed in a case study of heavy rainfall from a tropical system over the country on 8 February 2000. MITS identified the tropical nature of the system and successfully located areas of convective rainfall. MITS is available on the software system PCGRIDDS currently in operational use in South African forecasting offices. It operates on the prognostic fields generated by the South African Weather Service limited-area model Eta. Trial runs of MITS in the Central Forecasting Office of the South African Weather Service (SAWS) provided a positive response from weather forecasters and a full operational implementation is imminent.
This paper discusses issues that surround the development of empirical downscaling techniques as context for presenting a new approach based on self-organizing maps (SOMs). The technique is applied to the downscaling of daily precipitation over South Africa. SOMs are used to characterize the state of the atmosphere on a localized domain surrounding each target location on the basis of NCEP 6-hourly reanalysis data from 1979 to 2002, and using surface and 700-hPa u and v wind vectors, specific and relative humidities, and surface temperature. Each unique atmospheric state is associated with an observed precipitation probability density function (PDF). Future climate states are derived from three global climate models (GCMs): HadAM3, ECHAM4.5, CSIRO Mk2. In each case, the GCM data are mapped to the NCEP SOMs for each target location and a precipitation value is drawn at random from the associated precipitation PDF. The downscaling approach combines the advantages of a direct transfer function and a stochastic weather generator, and provides an indication of the strength of the regional versus stochastic forcing, as well as a measure of stationarity in the atmosphere–precipitation relationship.
The methodology is applied to South Africa. The downscaling reveals a similarity in the projected climate change between the models. Each GCM projects similar changes in atmospheric state and they converge on a downscaled solution that points to increased summer rainfall in the interior and the eastern part of the country, and a decrease in winter rainfall in the Western Cape. The actual GCM precipitation projections from the three models show large areas of intermodel disagreement, suggesting that the model differences may be due to their precipitation parameterization schemes, rather than to basic disagreements in their projections of the changing atmospheric state over South Africa. Copyright
Climate change is commonly evaluated as the difference between simulated climates under future and current forcings, based on the assumption that systematic errors in the current-climate simulation do not affect the climate-change signal. In this paper, we investigate the Canadian Regional Climate Model (CRCM) projected climate changes in the climatological means and extremes of selected basin-scale surface fields and its sensitivity to model errors for Fraser, Mackenzie, Yukon, Nelson, Churchill and Mississippi basins, covering the major climate regions in North America, using current (1961–1990) and future climate simulations (2041–2070; A2 and IS92a scenarios) performed with two versions of CRCM.
There has been a 38% decrease in expected annual rainfall totals over the Lowveld, in the eastern part of South Africa, during the last two decades. The downward trend in mean annual rainfall is not replicated in the rest of the summer rainfall region above the escarpment. Rainfall variability over the Lowveld has been increasing since about the 1950s, although the increase in variability appears to have been slowing down in more recent years. Changes in the frequency and intensity of El Nio/Southern Oscillation extreme events are only partly responsible for the observed desiccation and increase in rainfall variability. The CSIRO 9-level general circulation model simulates, for 2 CO2 conditions, an insignificant decrease of 10% in the annual mean and a slight increase in the inter-annual variability of rainfall over the Lowveld. Other general circulation models likewise simulate only small changes in annual mean rainfall over the region. However, the simulated increase in rainfall variability by the CSIRO 9-level model is likely to be conservative since the model, being linked to a slab ocean, is unable to represent important features of ocean-atmosphere coupling in the region. Significant changes in the frequencies of extreme drought events and of heavy rains in the Lowveld are likely to occur even with only small changes in the rainfall climatology of the region.
A brief review of climatic changes over the last 800 000 years in southern Africa is presented. The greatest emphasis is placed on those changes occurring during the Holocene and the period of meteorological record. Twentieth-century rainfall variations and their spatial manifestations are examined, and scenarios of possible future conditions are presented.
Regional climate modelling is becoming increasingly popular. The most common technique employs high resolution limited-area models to economically produce detaited climatologies for selected regions. A short review is presented of the underlying principles, recent simulations limitations of the method and future prospects.
The current state of regional climate and climate change modelling using GCMs is reviewed for southern Africa, and several approaches to regional climate change prediction which have been applied to southern Africa are assessed. Confidence in projected regional changes is based on the ability of a range of models to simulate present regional climate, and is greatest where intermodel consensus in terms of the nature of projected changes is highest. Both equil ibrium and transient climate change projections for southern Africa are considered. Warming projected over southern Africa is within the range of globally averaged estimates. Uncertainties associated with the parameterization of convection ensure that projected changes in rainfall at GCM grid scales remain unreliable. However, empirical downscaling approaches produce rainfall changes consistent with synoptic-scale circulation. Both downscaling and grid-scale approaches indicate a 10-15% decrease in summer rainfall over the central interior which may have important implications for surface hydrology. Climate change may be manifested as a change in variability, and not in mean climate. Over southern Africa, increases in the variability and intensity of daily rainfall events are indicated.
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