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Temporal and spatial trends of precipitation and river flow in the Yangtze River Basin, 1961–2000
Abstract
The suspected impact of climate warming on precipitation distribution is examined in the Yangtze River Basin. Daily precipitation data for 147 meteorological stations from 1961–2000 and monthly discharge data for three stations in the basin have been analyzed for temporal and spatial trends. The methods used include the Mann–Kendall test and simple regression analysis. The results show (1) a significant positive trend in summer precipitation at many stations especially for June and July, with the summer precipitation maxima in the middle and lower Yangtze River basin in the 1990s; (2) a positive trend in rainstorm frequency that is the main contributor to increased summer precipitation in the basin; and (3) a significant positive trend in flood discharges in the middle and lower basin related to the spatial patterns and temporal trends of both precipitation and individual rainstorms in the last 40 years. The rainstorms have aggravated floods in the middle and lower Yangtze River Basin in recent decades. The observed trends in precipitation and rainstorms are possibly caused by variations of atmospheric circulation (weakened summer monsoon) under climate warming.
... The Yangtze River Basin covers an area of 1.8 million square kilometers, and the mainstream is 6397 km long (Jiang et al., 2008). The Yangtze River Basin influences 19 provinces of China, accounting for 18.8% of China's land area (Jiang et al., 2007). The basin has abundant natural resources that support regional development for millions of people's social and economic needs. ...
... In short, this study confirms the significant influence of the Three Gorges Dam and Reservoir on the Yangtze River basin through analyses of the correlation pattern of precipitation and river discharge from different locations along the river. It also finds that the dam's influence on the climate is more significant than expected and reported in previous studies (Guo et al., 2012;Jiang et al., 2007;Li et al., 2021;Wei et al., 2014;Yin and Li, 2001). The influence of the dam is not limited to local climate and environment but have a clear impact on the whole river basin all the way to the coast which many researchers believe would not be significate and mitigated by the nature system. ...
The Three Gorges Dam and Reservoir on the Yangtze River is one of the world’s largest dams. After the dam’s construction in 1997, the reservoir started filling up, expanding to a size of over 600 km2. Therefore, its possible influence on maintaining the size and water level of this waterbody is significant and concerning. This research utilized wavelet coherence analysis to examine the temporal correlation and phase coherence among various datasets, including dam injection (1998–2018) and discharge (2003–2018) data, ground station precipitation data along the Yangtze River (1998–2020), and river discharge raster maps 1998–2018. The analysis revealed a strong coherence between dam operation and river discharge rates, as well as a minor seasonal coherence between dam operation and precipitation. The periodic properties of the datasets indicate that, in addition to the
general seasonal changes observed in the wavelet coherence analysis, other periodic signals in the datasets are also coherent over time. This coherence may be attributed to the simultaneous impacts of dam operation on precipitation and river discharge. The reasons for this coherence are still unknown, and further studies are
required, incorporating information on soil moisture, groundwater levels, air humidity, and the monsoon, to understand how the dam affects them.
... The average precipitation in the YRB showed high topographical dependence (Table 1). The mean annual and seasonal precipitation varied markedly over the basin, with in general less precipitation in the west that increased toward the east as the elevation decreases (Jiang et al. 2007). In terms of average annual precipitation, SST and TST showed much higher values than FST, with relative difference of 67% (SST to FST) and 121% (TST to FST), respectively. ...
... As the elevation decreased from FST to TST, the range of variation became YRB, FST, SST, and TST represent the VIMD of YRB, the first step terrain, the second stepterrain and the third step terrain, respectively larger, with outliers occurring in both SST and TST (Fig. 7a). Unusual precipitation in the three sub-regions is possibly caused by variations in atmospheric circulation under climate warming, which have been discussed in earlier studies (Jiang et al. 2007). The VIMD in the entire YRB ranged from − 1 × 10 -4 to −13 × 10 -4 kg m −2 s −1 between the 25th and 75th percentiles, with the median VIMD around −7.5 × 10 -4 kg m −2 s −1 (Fig. 7b). ...
Spatiotemporal variations in precipitation are closely related to vertically integrated moisture flux divergence (VIMD), where the extremes further cause natural disasters. Based on precipitation data from 151 meteorological stations in the Yangtze River Basin (YRB) for 1979 to 2019 and the meteorological reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), this paper studied the spatial and temporal characteristics of precipitation and VIMD and investigated their responsive relationship. The variations in precipitation and VIMD were examined using statistical methods, along with three step ‘staircases’ of terrain clusters dividing the whole basin based on descending altitude from west to the east. The results indicated that (1) the annual precipitation increased at a speed of 6.7 mm/10a during the study period: precipitation in spring, autumn and winter showed increasing trends, especially at the high elevation region (e.g., first step terrain), while a decreasing trend appeared in summer. (2) The VIMD trends in the YRB also varied in space and time, but overall, the summer trend pattern dominated the annual pattern. (3) The spatial distribution of VIMD agreed well with the topography clusters, where the first step terrain was dominated by convergence, and the second and third step terrains were dominated by divergence. (4) The average annual precipitation and seasonal precipitation showed responsive relationship with VIMD in terms of cumulative anomalies. Our results provided information on precipitation variability and revealed the characteristics of water vapor flux distribution as well as improved the understanding of the water transport mechanism in the YRB.
... Climate change is a long-term, gradual, an trend, while the weather is short-term, local, unstable, and unpredictable [3 usually a short-term process ranging from a few minutes to a few days. instantaneous or short-term atmospheric conditions in a specific area, su sunny, rainy, and snowy [35]. At the same time, climate change refers changes. ...
... Weather is usually a short-term process ranging from a few minutes to a few days. It refers to the instantaneous or short-term atmospheric conditions in a specific area, such as cloudy, sunny, rainy, and snowy [35]. At the same time, climate change refers to long-term changes. ...
In recent years, extreme weather has frequently occurred worldwide and caused significant disasters, including large-scale forest fires, rare heat waves, heavy rains, floods, and tornadoes. Those have caused unprecedented losses of human lives and property in some countries, affecting the livelihoods of many people. Climate change and natural disasters are the two hotspots of scientific research today, and there is a certain degree of correlation between the two. Although countries worldwide have long known about climate change and its threats to human existence and have been discussing countermeasures, they have still not been able to carry out concerted and practical actions. The study takes Canada as an example, and selects six representative provinces to evaluate the temporal change characteristics of extreme temperature at different sites. We use MATLAB software to perform multiple linear regression, linear fitting methods, and Pearson correlation analysis to analyze spatial changes and time-space trends. The method studies the relationship between the emergence of extreme weather and climate change and uses the evolutionary game theory to explore whether there is any contradiction between global warming and extreme local cold. The study found: (i) The maximum temperature of most provinces in Canada will be constantly higher, and the minimum temperature will be lower. Generally speaking, the average temperature of each year is slowly decreasing. (ii) The average temperature data of British Columbia (Eastern Pacific) and Quebec (West Atlantic) show that ocean temperature has a specific effect on land temperature in surrounding areas. (iii) Pearson correlation analysis shows that the emergence of extreme weather is closely related to climate change. (iv) The evolution path of the two-party game shows that global warming and the occurrence of extreme local cold are not contradictory. Under the conditions, there is a certain degree of synchronization between the two, interacting and influencing each other.
... The Middle Yangtze River (MYR) spans 955 km, stretching from the Yichang hydrometric station, situated immediately downstream of the TGD, to the Hukou hydrometric station (Fig. 1). The Yangtze Catchment is characterized by a subtropical monsoon climate, with over two-thirds of annual precipitation concentrated between June and October (Jiang et al., 2007). This strong seasonal contrast in rainfall leads to distinct flood and dry seasons. ...
... According to the modeling method of the BP neural network, 70% of the sampling points are used as training data, 15% of the data are used for model testing, and 15% of the data are used for result verification. After that, these sampling points were divided into five groups according to the change in altitude, which were <900 m, 900 m-1800 m, 1800 m-2700 m, 2700 m-3600 m, and >3600 m [39]. Finally, evapotranspiration, precipitation, temperature, population, and gross primary productivity were used as input layers, and forest carbon stocks were used as output layers to be modeled in Matlab 2021b. ...
It is of great significance to accurately assess the carbon sink capacity and trend of forest ecosystems on a regional scale, which is a key step to realizing sustainable forest management and carbon sink. Based on several remote sensing datasets, this study analyzes the dynamic characteristics of forest carbon stock in the Yangtze River Basin and its response to environmental factors using the Mann–Kendall nonparametric test, correlation analysis, and BP neural network during 2005–2020.
The results show that forest carbon stock in the Yangtze River Basin shows a fluctuating upward trend, with an average annual growth rate of 0.91%. Forest carbon stock in western high-altitude areas and areas with high human activity in the east showed a downward trend, while the central plains showed a stable growth trend. In the vast plains of the Yangtze River Basin, a suitable drought degree (−0.5 < SPEI < 0.5) is helpful to the accumulation of forest carbon reserves. In the future, rich forest resources should be fully developed to promote synergy between environmental protection and economic development from the perspective of developing green carbon trading, such as the carbon-sink forestry projects of CCER.
... The erosion of the Yangtze River channel leads to a reduction in groundwater levels in the majority of downstream regions, particularly in the impounding season . Since 1990, the upstream region of the Yangtze River has experienced a gradual decline in both precipitation and runoff in the impounding season (Jiang et al. 2007). The bathymetry of the Yangtze River and upstream climate change contributed to 14.17% and 17.08%, respectively, of the annual variation of MGL. ...
The Three Gorges Dam (TGD), located upstream of the Yangtze River, is the largest hydroelectric project in the world. The operation of TGD has changed the spatial and temporal distribution of streamflow in the middle and lower Yangtze River. The operation of TGD can also have varying degrees of impact on groundwater due to stream–aquifer interactions. Jianghan Plain is a major farming area in southern China, where groundwater is a critical source for domestic and agricultural use. Therefore, it is important to study the impact of the operation of TGD on the groundwater level in Jianghan Plain. Based on the STL algorithm, this study examined the interannual, annual, and random variations of groundwater levels in Jianghan Plain, analyzed and quantified the impacts of various factors including the operation of TGD that cause the spatial and temporal variation of the groundwater level. The results show that the operation of TGD can reduce the amplitude of the groundwater level and the frequency of extreme values. From upstream to downstream, the impact of TGD operation on the groundwater level shows a decreasing trend. The operation of TGD has a strong impact on the interannual variation within 6.71 km and annual variation within 5.77 km from the Yangtze River. The conclusions of this study can provide recommendations for local governments to develop groundwater management policies.
... Understanding the changes in precipitation at this scale is a prerequisite for sustainable water resource management in large river basins [19]. Jiang et al. [20] observed increased precipitation during monsoon season in the Yangtze River Basin from 1961 to 2000, especially in June and July. Zhang et al. [21] reported a possible increase in droughts caused by reduced spring and autumn precipitation, but they also stated an increase in winter precipitation in the Yellow River Basin during 1960-2009. ...
Precipitation is a key component of the hydrological cycle and one of the important indicators of climate change. Due to climate change, extreme precipitation events have globally and regionally increased in frequency and intensity, leading to a higher probability of natural disasters. This study, using the long-term APHRODITE dataset, employed six precipitation indices to analyze the spatiotemporal changes in extreme precipitation in the Pearl River Basin during 1951-2015. The Mann-Kendall (M-K) test was used to verify the significance of the observed trends. The results indicate that: (1) the interannual PRCPTOT showed a trend with an average positive increase of 0.019 mm/yr, which was followed by an increase in SDII, R95P, and RX1day, and a decrease in R95D and CWD; seasonal PRCPTOT also displayed an increase in summer and winter and a decrease in spring and autumn, corresponding to increases in R95P and SDII in all seasons. (2) The annual precipitation increases from the west to east of the basin, similar to the gradient distribution of SDII, R95P and RX1day, with the high R95D happening in the middle and lower reaches of the Xijiang River, but the CWD increased from the north to south of the basin. The seasonal spatial distributions of PRCPTOT, SDII, and R95P are relatively similar except in autumn, showing an increase from the west to east of the basin in spring and winter and a gradual increase from the north to south of the basin in summer, indicating that the Beijiang and Dongjiang tributary basins are more vulnerable to floods. (3) The MK test results exhibited that the Yunnan-Guizhou Plateau region in the upper reaches of the Xijiang River Basin became drier, and there was an increase in extreme precipitation in the Beijiang and Dongjiang river basins. The study results facilitate valuable flood mitigation, natural hazard control and water resources management in the Pearl River Basin.
... Recent studies have shown that the treatment efficiency for E. coli is lower within the same WWTP with increasing discharge due to reduced hydraulic retention times (Pallares-Vega et al., 2021;van Heijnsbergen et al., 2022). In combined sewer systems, WWTP discharge increases with rainfall (Mines et al., 2007), which also affects river flow (Bormann, 2010;Jiang et al., 2007;Pourfallah Koushali et al., 2021). Therefore, we used flow rates in receiving river segments as proxy for WWTP discharge and determined its correlation with logRed. ...
The proportion of wild swimmers at non-official bathing sites has increased during the Covid-19 pandemic. Bathing water quality at designated sites is monitored through analysis of the concentration of fecal indicator bacteria such as E. coli. However, non-official sites are generally not monitored. In a previous work, steady state modelling of E. coli was achieved at catchment scale, enabling a comparison of expected concentrations along an entire catchment for longtime average. However, E. coli concentrations can vary over several orders of magnitude at the same monitoring site throughout the year. To capture the temporal variability of E. coli concentrations on the catchment scale, we extended the existing deterministic E. coli sub-module of the GREAT-ER (Geo-referenced Exposure Assessment tool for European Rivers) model for probabilistic Monte-Carlo simulations. Here, selected model parameters are represented by probability distributions instead of fixed values. Wastewater treatment plant (WWTP) emissions and diffuse emissions were parameterized using selected data from a previous monitoring campaign (calibration data set) and in-stream processes were modeled using literature data. Comparison of simulation results with monitoring data (evaluation data set) indicates that predicted E. coli concentrations well-represent median measured concentrations, although the range of predicted concentrations is slightly larger than the observed concentration variability. The parameters with the largest influence on the range of predicted concentrations are flow rate and E. coli removal efficiency in WWTPs. A comparison of predicted 90th percentiles with the threshold for sufficient bathing water quality (according to the EU bathing water directive) indicates that year-round swimming at sites influenced by WWTP effluents is advisable almost nowhere in the study area. A refinement of the model can be achieved if quantitative relationships between the WWTP removal efficiency and both, the treatment technologies as well as the operating parameters are further established.
... Many studies have been carried out in South Asia. Jiang et al. (2007) studied the annual and seasonal trend of precipitation using MK and linear regression methods. Rana et al. (2012) used linear regression and MK statistics to explore the long-term trend in rainfall in Mumbai and Delhi. ...
The trend analysis of precipitation for four rain gauge stations and runoff for the Hayaghat station in the Bagmati river basin is carried out in this work by adopting modified Mann–Kendall and Sen's slope methods. Primary data and secondary data are used for finding the monthly, seasonal, and annual trends at four stations. Primary data are the observed rainfall from 1981 to 2013 which are collected from IMD Pune, observed runoff data are collected from CWC Patna and secondary data are the National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis rainfall data for the period 1981–2013. The research objectives are (i) to determine rainfall and runoff trend analysis, as well as the relationship between observed rainfall data and NCEP/NCAR reanalysis secondary data for four stations and (ii) to correlate between observed rainfall data and runoff data for all four seasons. The correlation analysis of observed rainfall and NCEP/NCAR reanalysis data shows a very good correlation ranging between 0.6111 and 0.7435. It is found that the trend of rainfall is increasing in the period of monsoon and post-monsoon at all selected stations except the monsoon season in Dhenge. Correlation analysis of rainfall and runoff shows a comparatively good correlation which ranges from 0.3724 to 0.4721 for all four seasons.
HIGHLIGHT
The goals of this research are (i) to determine rainfall and runoff trend analysis, as well as the relationship between observed rainfall data and NCEP/NCAR reanalysis secondary data for four stations and (ii) to correlate between observed rainfall data and runoff data for all four seasons.
... Due to the difference in topography, closed high-and lowtemperature central areas, such as the Sichuan Basin, Yunnan-Guizhou Plateau, and Jinsha River valley, are formed under the above general distribution trend (Xiao et al., 2015). Droughts and floods occur in the basin, which has a certain impact on the safety of life and property in the basin (Yang et al., 2021;Jiang et al., 2007). In addition, the YRB can be divided into 12 secondary sub-basins based on the water resources management needs of the Ministry of Water Resources of the People's Republic of China (Table 1). ...
Global precipitation has undergone significant changes due to climate change, resulting in extreme drought and flood events and remarkable losses of life and property. Therefore, based on precipitation and temperature data for the Yangtze River Basin (YRB), as well as teleconnection indices (i.e., Nino3.4, North Pacific Index [NPI], Southern Oscillation Indices [SOI], and Pacific Decadal Oscillation [PDO]), the causal relationship between the teleconnection indices and the dry/wet changes was analyzed and explored using the standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI) from 1961 to 2018. Based on the findings, precipitation significantly increased in the upper and lower reaches of the YRB, with a maximum increase of 8 mm/a, and decreased in the middle reaches, with a maximum decrease of 4 mm/a. Further, the temperature in the entire YRB increased, with a maximum increase of 0.04 °C/a. The drought characteristics derived from SPI in the YRB were more uniform in spatial distribution from 1961 to 2018, with small local differences and the largest proportion of mild droughts in different drought classes; however, for those from SPEI in the YRB, local differences in spatial distribution and the largest proportion of moderate droughts in different drought classes were found. Finally, both linear and nonlinear causality between the teleconnection indices and the wet/dry changes in the YRB were significant to some extent, especially for NAO, Nino 3.4, and PDO. These causalities between the wet/dry changes and the teleconnection indices were also more significant for short periods. Related studies are important for assessing the driving forces of dry–wet changes in the YRB.
... In this study, various methods were used to detect changes in surface runoff in the MYRB. The surface runoff trends of different monthly, seasonal, and annual series were found to be different (Jiang et al. 2007). This suggests that changes in climatic factors have specific impacts on surface runoff changes. ...
Changes in surface runoff and its coupling relationship with atmospheric circulation have been an ongoing focus of climate change research. In this study, the Mann–Kendall test, Pettitt test, and quantile regression were used to analyze changes in surface runoff in the middle reaches of the Yangtze River Basin (MYRB) during 1902–2014 based on the global runoff reconstruction (GRUN) dataset. In addition, cross wavelet analysis was used to analyze the coupling relationships between four teleconnection indices from the National Oceanic and Atmospheric Administration (NOAA) website (i.e., East Central Tropical Pacific SST (El Niño 3.4), Pacific Decadal Oscillation (PDO), Eastern Pacific/North Pacific Oscillation Index (EP/NP) and multivariate ENSO Index (MEI V2)), and monthly average surface runoff series in the MYRB. The study produced several important results: (1) Trends in the annual surface runoff, from 1902 to 2014, in the MYRB have changed significantly, with the longest and most significant upward trend occurring from 1987 to 2000. (2) The annual series surface runoff mutation years varied across the MYRB (e.g., surface runoff in the central region changed abruptly around 1918, whereas surface runoff in the northern and southern regions changed abruptly around 2000). (3) Significant correlations (P < 0.05) between the surface runoff in the MYRB and the four representative teleconnection indices (e.g., El Niño 3.4, PDO, EP/NP, and MEI V2) indicate that surface runoff has been strongly linked to the indices. The significance of this study lies in its revelation of relationships between water resources system changes and climate change.
... Changes in rainfall have caused changes in ecosystems (Padilla et al. 2015) and ultimately changes in land use patterns and topography. (Wei et al. 2009) Sometimes these changes lead to an increase in annual and seasonal runoff changes in the Korean River sub-basin showed that in the north of this region the trend of change is increasing and, in the south, it is decreasing and the flow rate is different in different seasons (Altınak and Baraeb 2014; Jiang et al. 2007) and precipitation changes are the main cause of flow change (Zhang et al. 2011). Changes in runoff time series were investigated using the Mann-Kendall test in Thuringia, Germany (Danneberg 2012). ...
One of the characteristics of arid and semi-arid regions is low rainfall and lack of uniform distribution throughout the year, which has a direct effect on water resources in these regions. In this research, daily precipitation and flow rate data of 39 meteorological stations and 9 hydrometric stations in the period 1994–2015 have been used. To evaluate seasonal and annual changes, the average data was calculated, and also MK and SQMK tests were used to detect the type of trend and mutations of changes. Sen slope, correlation, and Pettitt tests were used to determine the slope of changes, type of relationship, and also to determine the breaking point in the data time series, respectively. The results show that in all seasons, Tashk, Bakhtegan, and Maharloo sub-basins had the highest average rainfall; however, flow rate and precipitation changing curve in this region has decreased. The time-changing curve in precipitation is decreasing in winter and spring and increasing in summer and autumn. Thus, the spatial study of the udic moisture regime shows an increase in systems' activity that affects the region in the hot (summer) and cold (autumn) seasons. The trend of leap changes in winter and summer (autumn) in 7 sub-basins with 95% confidence level has been decreasing (increasing) which has decreased (increased) the river water flow in these areas. The highest percentage of decreasing and increasing changes in precipitation is in region 9 with values of − 6.66 and 2.55. The trend of leap changes in annual precipitation and flow rate in 5 sub-basins with a 95% confidence level has been reduced. The decrease in rainfall in areas 8 and 9 have had a direct effect on flow rate and has caused a significant decrease. The correlation between rainfall and flow is positive in all sub-basins and the highest coefficient of determination is in regions 3 and 9 with 40%.
... Gaining a comprehensive understanding of the effects of oceanic-atmospheric climate anomalies and solar activity on temporal variability of precipitation and streamflow in specific watersheds is of great significance for hydrological simulation, climate change and risk management as well as for addressing water-resource-related issues [3,30,31]. Due to its proximity to the Pacific Ocean, the Yangtze River basin is prominently sensitive to such climatic phenomena as El Niño-Southern Oscillation (ENSO) [32][33][34][35][36] and Pacific Decade Oscillation (PDO) [33,35,37,38], which have significant implications for forecasting water resources and climate conditions. In recent years, studies in the Yangtze River basin and its tributaries have made significant advances in the influence of large-scale teleconnection patterns on hydrological variability [33,35,37,[39][40][41][42][43][44][45], while the temporal persistence of these relationships is not yet wholly understood. ...
Profiling the hydrological response of watershed precipitation and streamflow to large-scale circulation patterns and astronomical factors provides novel information into the scientific management and prediction of regional water resources. Possible contacts of El Niño–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), sunspot activity to precipitation and streamflow in the upper Yangtze River basin (UYRB) were investigated in this work. Monthly precipitation and streamflow were utilized as well as contemporaneous same-scale teleconnections time series spanning a total of 70 years from 1951 to 2020 in precipitation and 121 years from 1900 to 2020 in streamflow. The principal component analysis (PCA) method was applied so as to characterize the dominant variability patterns over UYRB precipitation time series, with the temporal variability of first two modes explaining more than 80% of total variance. Long-term evolutionary pattern and periodic variation characteristics of precipitation and streamflow are explored by applying continuous wavelet transform (CWT), cross-wavelet transform (XWT) and wavelet coherence (WTC), analyzing multi-scale correlation between hydrological variables and teleconnections in the time-frequency domain. The results manifest that ENSO exhibits multiple interannual period resonance with precipitation and streamflow, while correlations are unstable in time and phase. PDO and sunspot effects on precipitation and streamflow at interannual scales vary with time-frequency domains, yet significant differences are exhibited in their effects at interdecadal scales. PDO exhibits a steady negative correlation with streamflow on interdecadal scales of approximately 10 years, while the effect of sunspot on streamflow exhibits extremely steady positive correlation on longer interdecadal scales of approximately 36 years. Analysis reveals that both PDO and sunspot have significantly stronger effects on streamflow variability than precipitation, which might be associated with the high spatiotemporal variability of precipitation.
... ere was a correlation between flow and precipitation (r � 0.35); the relationship direction was positive, and the correlation intensity was moderate. Researchers have reported different ranges of correlation coefficients in earlier studies; however, some [59,60] have reported moderate-to-severe dependence between rainfall and river flow, arguing that the correlation coefficient is approximately 0.50. e mild correlation coefficient between rainfall and river flow can be due to the entry of a constant amount of domestic wastewater into the river, which is not affected by the amount of rainfall. ...
This paper aims to investigate the effects of natural variables, including precipitation and flow rate, on the quality of the Zarjoub River in Guilan province, Iran. The new hydrological insight in this study is a lack of national research focused on the dual effects of rainfall and flow rate on river water quality in coastal areas along the Anzali Wetland. To investigate the effect of precipitation and flow rate on river water quality, nine water quality variables were monitored during the 10-year period. In this article, (a) the existence of trends and the best fitted models of water quality parameters and the discharge and precipitation were analysed using statistical techniques and (b) the relationships between concentration of constituents with the discharge and precipitation on the up-stream and middle station were also examined. Box plots, for explaining the distribution of a data collection, were used. The results showed the existence of trend of water quality parameters with river flow and rainfall. As presented in Section 3, with increasing precipitation and flow rate, concentration of all constituents, except pH and SO₄2, decreased. On the contrary, the maximum amount of water quality elements was observed in low precipitations; therefore, the maximum concentration occurred in less than 15 mm precipitation. Simple regression was used to evaluate the discharge concentration and precipitation concentration. According to the correlation coefficient (r), the relationship between concentration and precipitation is weaker than (0.238) discharge concentration (0.699). The results further showed climate change and river water quality to be related.
... To investigate the trend of extreme rainfall events, various methods such as MK (Mittchell et al. 1966), moving t-test technique Cox-Stuart, and Pettitt's (P) tests have been applied, and nonstationary generalized extreme value models have been developed (Wu et al. 2015). However, most previous studies focused only on a certain aspect of precipitation regimes, such as precipitation means ( Jiang et al. 2007;Chen et al. 2014), precipitation maxima (Lü et al. 2018), or selected only a limited number of precipitation indices (Guo et al. 2013;Zhang et al. 2013). In the research of climate change, global climate model and regional climate model datasets have been used to determine the intensity and frequency of precipitation, which may become more critical in the late 21st century (Singh & Xiaosheng 2019;Sharma & Goyal 2020). ...
A small change in the mean climate may lead to a dramatic change in the frequency and intensity of extreme climate events. In this study, the relationship between mean temperature (MT) and extreme precipitation and the influence from large-scale circulation were investigated in Hunan Province. The correlation between MT and the frequency of extreme precipitation events in different seasons (spring, summer, and autumn) and time periods (1960–2009) was used to obtain pairs of spatial patterns by the singular value decomposition method. The temporal expansion series displayed a consistent trend of temperature and extreme precipitation, and a mutation was observed to occur approximately during the 1980s–1990s. Temperature exhibited a warming trend after the mutation, but the frequency of extreme precipitation events exhibited obvious spatio-temporal variations. The causes of seasonal differences in the frequency of extreme precipitation events were determined by comparing interdecadal changes in three atmospheric circulation factors (850 hPa winds, the entire layer of vapor transportation fluxes and vapor flux divergence) before and after the mutation was revealed. HIGHLIGHTS
The relationship between temperature and extreme rainfall events was investigated using the SVD method.;
The temperature exhibited a sudden change during the 1980s–1990s.;
The trend of temperature change was widely varied.;
The correlation between temperature and extreme rainfall exhibited a significant spatial variation.;
The wind anomaly field revealed the opposite trends before and after the abrupt change.;
... Aiming at striking a good balance between frequency and time, the ω 0 was chosen to be 6 [68]. According to [27], the cross-wavelet spectrum of two time series, for example, W NPM and MEI, can be defined as C W NPM,MEI i (j): ...
Water level (WL) and terrestrial water storage (TWS) are two important indicators for early alerts of hydrological extremes. Their variation is governed by precipitation under monsoon variability, in particular in the Mekong river basin, where it is affected by the interaction between the Indian summer monsoon (ISM) and western North Pacific monsoon (WNPM). This study aimed to quantify the contributions of two monsoons to the water levels of four hydrological stations (i.e., My Thuan, Can Tho, Chau Doc and Tan Chau) on the Mekong Delta and the terrestrial water storage of the entire Mekong River basin through relative importance analysis. Three methods—multivariate linear regression; Lindeman, Merenda and Gold (LMG); and the proportional marginal variance decomposition (PMVD) methods—were selected to quantitatively obtain the relative influence of two monsoons on water level and TWS. The results showed that, from 2010 to 2014, the proportions of the ISM impacts on the water level obtained with the three methods ranged from 55.48 to 81.35%, 50.69 to 57.55% and 55.41 to 93.64% via multivariate linear regression, LMG and PMVD, respectively. Further analysis showed that different choices of time spans could lead to different results, indicated that the corresponding proportion would be influenced by other factors, such as El Niño–Southern Oscillation (ENSO). The removal of ENSO further enlarged the relative importance of the ISM, and the mean values of the four stations were increased by 8.78%, 2.04% and 14.92%, respectively, via multivariate linear regression, LMG and PMVD. Meanwhile, based on the analysis of terrestrial water storage, it was found that the impact of the ISM on the whole Mekong River basin was dominant: the proportions of the impact of the ISM on terrestrial water storage increased to 68.79%, 54.60% and 79.43%, which rose by 11.24%, 2.96% and 19.77%, respectively, via linear regression, LMG and PMVD. The increases almost equaled the quantified proportion for the ENSO component. Overall, the novel technique of quantifying the contributions of monsoons to WL and TWS can be applied to the influence of other atmospheric factors or events on hydrological variables in different regions.
... With the large-scale development of hydropower, the hydrological regimes in the basin, especially the spatial-temporal distribution of runoff at the outlet control hydrometric station, have presented a new situation, which also changes the flood regimes, therefore negatively affecting the efficiency of the planning and design of water conservancy projects and flood prevention management (Yao et al., 2006). There have been a lot of research results on the change characteristics of runoff and their attribution analysis in the Yangtze River (Jiang et al., 2007;Chen et al., 2014;Wei et al., 2014;Yang et al., 2015). However, research about the all-round change characteristics of flood regime is relatively few, and how to quantitatively evaluate the Three Gorges Dam's (TGD) effect on peak-flood clipping is worthy of discussion. ...
River flooding affects more people worldwide than other natural hazards. Thus, analysis of the changes in flood regime caused by global warming and increasing anthropogenic activities will help us make adaptive plans for future flood management. The nonstationary flood behavior in the upper Yangtze River was examined comprehensively in terms of trend, change point, and periodicity with co-usage of different methods. Results show that there are decreasing tendencies in the corresponding series of annual maximum flood peak flow and flood volume in four out of six control stations, except Pingshan and Wulong stations in the Jinsha River and the Wu River, respectively, and the flood peak occurrence time appears earlier mostly. The uniformity of flood process increases in four main tributaries, while it decreases in mainstream of the Yangtze River (Yichang and Pingshan stations). The rates of both rising limb and recession limb of all the typical flood process flowing through the six stations were analyzed. 77.8% of the rates of rising limb decrease, while 61.1% of the rates of recession limb increase, which is almost consistent with the variation reflected by the uniformity. The change points of most evaluation indicators happened in 1970s–1990s. The first main periodicity of evaluation indicators in Yichang is about 45 years, while that of other stations is about 20 years. Invalidity of stationarity in the flood series can be attributed to the intensified construction on major water conservancy projects, changes of underlying surface, and influences of climatic variables. The contributions of both climatic control and the Three Gorges Dam (TGD) to the variation of the annual flood peak in Yichang station were further quantitatively evaluated, which has verified that the construction of the TGD has played a positive role in peak-flood clipping.
... Rainfall is an important parameter in weather forecasting and flood control. How to obtain rainfall information more quickly and accurately has attracted more and more attention from meteorological researchers [1,2]. Nowadays, meteorological disasters such as droughts and floods frequently occur and cause serious losses. ...
To further reduce the error rate of rainfall prediction, we used a new machine learning model for rainfall prediction and new feature engineering methods, and combined the satellite system’s method of observing rainfall with the machine learning prediction. Based on multivariate correlations among meteorological information, this study proposes a rainfall forecast model based on the Attentive Interpretable Tabular Learning neural network (TabNet). This study used self-supervised learning to help the TabNet model speed up convergence and maintain stability. We also used feature engineering methods to alleviate the uncertainty caused by seasonal changes in rainfall forecasts. The experiment used 5 years of meteorological data from 26 stations in the Beijing–Tianjin–Hebei region of China to verify the proposed rainfall forecast model. The comparative experiment proved that our proposed method improves the performance of the model, and that the basic model used is also superior to other traditional models. This research provides a high-performance method for rainfall prediction and provides a reference for similar data-mining tasks.
... The Southeast River Basin and the Pearl River Basin were not included because they were composed of many medium and small size rivers. Due to the large size and different hydrological characteristics [29], the Yangtze River basin was divided into two sub-basins: The upper Yangtze and the mid and lower Yangtze by the longitude of Yichang City (111.3 • E) (Figure 1), which the upper reaches of the Yangtze River refers to the section from the source of the Yangtze River to Yichang Station, and the middle and lower reaches of the Yangtze River refers to the part of the Yangtze River from Yichang Station to the estuary. The river basins included in this study are the Songhua, Liaohe, Haihe, Huaihe, and Yellow rivers, the upper Yangtze river, and the mid and lower Yangtze river. ...
The causes of the pan-evaporation decline have been debated, and few researches have been carried out on the possible effect of local land use and land cover change on the regional pan-observation data series. In this paper, the urbanization effect on the estimate of pan-evaporation trends over 1961–2017 was examined for the data series of 331 urban stations, applying a previously developed dataset of the reference stations, in seven large river basins of the China mainland. The trends of pan-evaporation difference series (transformed to anomaly percentage) between urban stations and reference stations were negative and statistically significant in all of the basins, indicating that urbanization significantly reduced the pan-evaporation. The urbanization-induced trend in the whole study region was −2.54%/decade for the urban stations. Except for the Yellow River Basin and the upper Yangtze River Basin, the urbanization effects in the other five large river basins of the country are all significant, with the mid and low reaches of the Yangtze River and the Songhua River registering the largest urbanization effects of −4.08%/decade and −4.06%/decade, respectively. Since the trends of regional average series for reference stations across half of the river basins are not statistically significant, the urbanization effect is a dominant factor for the observed decline in pan-evaporation. This finding would deepen our understanding of the regional and basin-wide change in pan-evaporation observed over the last decades.
... Additionally, Partal and Kahya (2006) identified trends in the long-term monthly average and annual average rainfall series between 1929 and 1993. Jiang et al. (2007) examined spatial and temporal trends of daily precipitations from 147 weather stations for the period of 1961-2000, while Türkeş et al. (2009) examined the longterm trends of annual, seasonal, and monthly total precipitations utilizing 97 stations for the period from 1930 to 2002. Moreover, Yavuz and Erdogan (2012) examined the annual and monthly precipitation trends for 120 stations during 2009. ...
The description and analysis of rainfall trends is necessary for effective planning, management, and exploitation of water resources. This study investigates the possible trend of precipitation of 28 stations in a semi-arid Mediterranean environment (Northern Algeria) for the period from 1959 to 2019 (60 years), using a recently proposed innovative partial trend methodology. The main advantage of this new method is that it provides qualitative interpretations of trends in the high, medium, and low precipitation ranges in terms of the structure of the time series’ internal trend. An accurate database has been established thanks to the homogeneity of the data quality leading to rather satisfactory results with a precision of the spatial and temporal tendencies, thus establishing maps of regional trends: “high precipitation,” “average precipitation,” and “low precipitation” for the whole study area.
... , was calculated and replaced in place of significantly autocorrelated time series [41]. Thus, pre-whitened [43,44] time series were used to identify the statistically significant changes over time The Mann-Kendall test has been used for the identification of time series trends in hydro-climatological data [41,[45][46][47][48]. Wang [49] found that non-parametric methods were better when compared to parametric trend determination methods because they are less sensitive to outliers. ...
Aerosol Optical Thickness (AOT) is one of the important parameters for assessing regional and global level of climate change. Fog episodes have considerably increased in south Asia because of environmental factors, and the burning of agricultural residue leads to major social and economic problems. In present study, Mann-Kendall trend analysis of AOT and active fire events was done, and their significance were assessed using long-term (October 2012-February 2020) remote sensing data derived smog maps. Visible Infrared Imaging Radiometer Suite National Polar Partnership (VIIRS N-PP) was used to map AOT episodes over the northern region of Pakistan and India. Results reveal that AOT displays a significantly decreasing trend over the northern and eastern region of Pakistan and a similar decreasing trend from the Western to Eastern region of India. Furthermore, active fire events have a significantly increasing trend at the Northern region of Pakistan. However, fire events have a significantly decreasing trend over the southern and southeastern region of India. Additionally, statistically significant decreasing trends were observed for AOT over Chakwal (p-value = 0.2, Z_MK = −2.3) and Patiala (p-value = 0.15, Z_MK = −3.2). Fire events have a significantly increasing trend for Dera Ismail Khan (p-value = 0.01, Z_MK = 1.9), Jhang (p-value = 0.01, Z_MK = 1.9), and Chakwal (p-value = 0.01, Z_MK = 1.8), while they are significantly decreasing trend near New Delhi (p-value = 0.2, Z_MK = −0.9), Aligarh (p-value = 0.15, Z_MK = −0.9) and Patiala (p-value = 0.2, Z_MK = −0.8).
China's coastal waters are confronting serious water quality problems, particularly the Hangzhou Bay in the Yangtze River Delta. To find out the underlying cause, we use the Regional Ocean Modeling System (ROMS) to simulate the hydrodynamic characteristics and the evolution of water pollutants. The results show that the hydrodynamic conditions are complicated and the semi-exchange time is 46 days, significantly hindering the dilution and diffusion of water pollutants. Concentrations of each typical pollutant as chemical oxygen demand (COD), dissolved inorganic nitrogen (DIN), and phosphate (PO4) decrease from west to east, showing an obvious enrichment in the coastal region. Source-oriented results show that the inland water pollution of the Yangtze River and the Qiantang River is the key contributor, and the sewage outfalls on the coast near the bay worsen the pollution. This suggests that the government needs to strengthen the management of sources that affect water security.
An accurate and reliable precipitation product on regular grids is essential for understanding trends and variability within climate studies, for weather forecasting, and in hydrology and agrometeorology applications. However, the construction of high-resolution spatiotemporal precipitation grid products is challenging for complex terrain with sparse rain gauge networks and when only coarse spatial resolutions of satellite data are available. The objective of this study was to consequently provide a practical method to create a grid precipitation product by merging accurate quantitative observations from weather stations with continuous spatial information and from a satellite-based estimate product. The new gridded precipitation product exhibits a monthly temporal resolution and a spatial resolution of 0.01° for the Tian Shan range, extending back to 1981. To overcome the limitation of low densities and sparse distributions of meteorological stations in the complex terrain of the Tian Shan, a suitable interpolation of Australian National University Spline (ANUSPLIN) was used to interpolate grid precipitation based on in situ data. The interpolation grid precipitation was then merged with the satellite precipitation product developed by the U.S. Geological Survey and the Climate Hazards Group. After evaluation and validation using withheld stations and comparison to reference datasets, the result indicated that the merged product exhibits considerable promise for application in complex terrain. The method can be widely applied and is expected to construct precipitation products with high spatial and temporal resolution by merging multiple precipitation data sources.
Significance Statement
The purpose of this study is to construct a gridded precipitation dataset by merging the interpolation precipitation based on in situ observation and a satellite precipitation product in arid mountain regions. This is important because gridded precipitations are essential to the evaluation of climate model output and detection of trends in mean climate and climate extremes. Our results present a guide on merging frameworks to construct precipitation datasets used multisource data sources for regions with complex topography, precipitation scarcity, and ungauged and sparse collection.
Satellite remotely sensed solar-induced chlorophyll fluorescence (SIF) is an effective index for detecting the ecosystem-level photosynthetic capacity, yet it remains poorly understood how vegetation photosynthesis responds to water constraints. This study determined the spatial–temporal changes and water constraints on vegetation photosynthesis based on the Self-Calibrated Palmer Drought Severity Index (scPDSI), Standardized Precipitation Evapotranspiration Index (SPEI) and global Orbiting Carbon Observatory-2 SIF (GOSIF) data in the Yangtze River and Yellow River basin between 2000 and 2018. The results showed that annual maximum GOSIF steadily increased across the whole basin (slope = 0.0031 W m⁻²μm⁻¹sr⁻¹a⁻¹, P < 0.001). The maximum increasing trend was found in the semi-arid region (0.0034 W m⁻²μm⁻¹sr⁻¹a⁻¹, P < 0.001). The highest value of annual maximum GOSIF was found in the Qinling-Daba Mountains along with Hengduan Mountain. The lowest GOSIF was found in the western portions of the Loess Plateau and the source region of Yangtze River and Yellow River. Positive correlations between satellite GOSIF and water availability were particularly strong in the Loess Plateaus; in contrast, negative correlations were found in the Hengduan Mountains. The area of water deficit displayed a significant trend towards expansion (slope = 1.539 % a⁻¹ and 0.898 % a⁻¹, P < 0.05), while water surplus areas significantly shrank (slope = 0.847 % a⁻¹ and 0.584 % a⁻¹, P < 0.05) in the Yangtze River and Yellow River basin. Atmospheric CO2 concentration and precipitation were the dominant drivers for the water deficit regions, while atmospheric CO2 concentration and temperature were the dominant drivers for the water surplus regions. This study emphasizes the effect of water constraints on regional vegetation photosynthesis under global warming conditions and patterns of greening.
In this study, the trends in river discharge were investigated on different time scales for the period 1951/52–2009/10 over the northern part of the Korean peninsula based on the reliable flow datasets measured at the stations with near-natural states, and no or less anthropogenic activities. The annual mean discharge decreased by 5–11%/decade and its abrupt years appeared around 1980. On the seasonal scale, the trends in the rainy season were the most definitely observed with the decreasing rate of 6–12%/decade and could be seen to begin earlier than the annual trends. Unlike the annual and seasonal trends, the monthly trends exhibited very fluctuant variations depending on the individual months and locations. Overall, considering the detected significant trends, there is strong evidence that the river discharge remarkably decreased with the enhanced variability and the decreasing trends were a predominant part of the changes in the river discharge in the study period. With regard to the hydrological regions, the result suggested that the river discharge in the coastal hydrological regions influenced by the oceanic climate could be more sensitive to climate change than in the northern inland area with the continental climate.
کنترل آلودگی رودخانه کر به عنوان یکی از شاهرگ های حیاتی آب کشاورزی، صنعت و شرب، نقش مهمی در كيفيت منابع آب منطقه ایفا مي کند. در این مطالعه به منظور شناخت بهتر عوامل آلاينده، روند تغییرات کیفیت آب رودخانه کر در بازه زماني 46 ساله، در دو ایستگاه چمریز در بالادست، و پل خان در پایین دست رودخانه، توسط آنالیزهای من کندال و رگرسیون خطی بررسی گرديد. توزیع های آماری بر پارامترهاي كيفي آب، برازش، مقادير پارامترها در دوره بازگشت های مختلف پیش بینی، و مقادیر بالادست و پایین دست مقایسه گرديد. سپس کیفیت آب جهت مصارف شرب، دام و طیور و کشاورزی، با مقايسه با استانداردها، بررسي گرديد. نتايج نشان داد که در چمریز ميانگين كليه پارامترها در محدوده استاندارد مصارف مذكور قرار دارد. در پل خان TDS و EC بالاتر از حد استاندارد شرب، و سایر پارامترها در محدوده می باشد. به غير از EC كه در محدوده مصرف دام و طيور، و آبياري نيز قرار ندارد، ساير پارامترها در محدوده مصارف مي باشد. مقايسه مشخصه های آماری نشان داد كه بجز PH، میانگین ساير پارامترها در پل خان از چمریز بیشتر است. روند زماني نشان داد كه در چمریز تنها Na و SAR بدون روند هستند. SO4، TH وPH روندي کاهشی، و EC، HCO3،Cl ،Ca ،Mg وTDS روندي افزایشی داشته اند. در پل خان همه متغیرها دارای روند مي باشند، بطوريكه TH و PH روندي کاهشی و ساير متغيرها روندي افزایشی دارند. بجز PH، مقادير پيش بيني شده كليه پارامترها، در همه دوره بازگشت ها، در پل خان از چمريز بيشتر است. با استفاده از روابط رگرسیون حاصله می توان مقادير متغيرها را در آینده پیش بینی نمود. كاهش آلاینده هاي شیمیایی کشاورزی، جلوگیری از ورود فاضلابها به رودخانه و یا تصفیه آنها می تواند در کنترل روند نزولي كيفيت موثر باشد.
بررسی روند زمانی دبی جریان اطلاعات عملی مفیدی جهت مدیریت بهتر منابع آب در عصر تغییر اقلیم فراهم می آورد. تغییرات اقلیمی از چالش های مهم زیست محیطی عصر کنونی است. نوسانات متغیرهای هواشناسی از جمله بارندگی اثرات شدیدی بر منابع آب سطحی و زیرزمینی و خاک دارد. بررسی تغییرات کمیت آب رودخانه ها و میزان تاثیرپذیری آنها از فعالیت های انسانی و طبیعی از اهداف ارزیابی روند زمانی دبی رودخانه ها می باشد. رودخانه كر يكي از منابع اصلی آب سطحي استان فارس است كه زندگي هزاران كشاورز منطقه به آن بستگي دارد و درصد بالايي از آب آشاميدني شهرهاي شيراز، مرودشت و روستاهاي مسير را تأمين مي كند..در تحقیق حاضر روند سری زمانی داده های دبي آب در ایستگاه چمریز واقع در بالادست و پل خان در پایین دست رودخانه کر، با استفاده از آنالیزهای آماری من کندال و رگرسیون خطی مورد بررسی قرار گرفت و مقایسه گردید. همچنین توزیع های آماری بر داده های میانگین ماهانه دبی، برازش داده شده و دبی در دوره بازگشت های مختلف پیش بینی و مقادیر مقایسه شد. مقایسه میانگین داده های دو ایستگاه نشان داد که میانگین دبی آب ایستگاه پل خان از چم ریز بیشتر است که به دلیل ورود رودهای دیگری مانند سیوند به رود کر می باشد. مقایسه مقادیر دبی آب ایستگاه ها نشان داد که در دوره بازگشت های 2، 5 و 10 سال مقادیر دبی ماهانه ایستگاه پل خان بیشتر از چمریز است، اما در دوره بازگشت های 20 و 50 سال دبی در چمریز بیشتر است، که می تواند به دلیل کنترل جریان سیلاب در سد درودزن باشد. نتایج تحلیل روند دبی رودخانه کر نشان داد که در هر دو ایستگاه پل خان و چمریز دبی روندی کاهشی داشته است. کاهش بارندگی و خشکسالی های اخیر، همچنین افزایش سطح زیرکشت و برداشت بی رویه از آب رودخانه برای مصارف مختلف می تواند دلیلی بر روند کاهشی دبی این رودخانه باشد. از نتایج حاصله می توان در برنامه ریزی بهره برداری پایدار از منابع آب بهره گرفت.
در دهه هاي اخير افزايش ميانگين دماي هوا ناشي از تغييرات گازهاي گلخانهاي اتمسفر مورد توجه محققين در مناطق مختلف هان قرار گرفته اسه .
يكي از آثار مهم تغييرات مذكور افزايش نياز آبي گياهان اس . هدف اين مطالعه بررسي روند تغييرات ET0 در ايستگاه خشک زابل ميباشهد. بهراي بررسهي
ميزان ET0 روش پنمن-مانتيس )PM )انتخاب و مورد استفاده قرار گرف . براي اين منظهور داده ههاي ايهن ايسهتگاه از سها 1963 تها 2005 جمه آوري و
تكميل شد. سپس ميزان ET0 زابل در هر ماه و سا با روش PM محاسبه و روند تغييرات سري زماني ET0 در هر ماه بهه طهور جداگانهه بها روش مهن -كنهدا
)MK )مطالعه شد. نتايج نشان داد كه ميزان متوسط دوره آماري ET0 اين ايستگاه از 08/2 ميليمتر بر روز در ماه دسامبر تا 8/14 ميليمتر بر روز در ماه ژوئيهه
تغيير ميكند. روند تغييرات ET0 در طو دوره آماري براي تمام ماههاي سا مثب و معني دار بود. ضعيف ترين روند متعلق به ماه ژوئن با سهط معنهي داري
05/0 بود. در حالي كه قوي ترين روند متعلق به ماه فوريه با سط معني داري 01/0 بود. نتيجه اين مطالعه نشان داد كه عل وجود روند مثب در سريههاي
ET0 در ايستگاه زابل غالبا به عل افزايش سرع باد در طو دوره آماري مورد مطالعه بوده اس .
The spatial and temporal characteristics of global precipitation have changed significantly under climate change, increasing the difficulty of solving water security problems. Therefore, understanding changes in global precipitation is of great importance to comprehend and solve water security problems. This study analyzed the characteristics of drought and flood alternation in the Yangtze River Basin (YRB) based on precipitation data, and explored the driving forces of drought and flood alternation by combining relevant meteorological factors (i.e., temperature [Tem], relative humidity [Rh], wind speed [Win], and actual evaporation [ETa]) and teleconnection indices (i.e., Nino 3.4, Pacific Decadal Oscillation [PDO], Southern Oscillation Indices [SOI], North Pacific Index [NPI], and Atlantic Multi-decadal Oscillation [AMO]). The main conclusions are as follows: (1) The spatial and temporal characteristics of precipitation in the sub-basins of the YRB varied widely, with significant annual precipitation trends ranging from −5 to 9 mm/year (p < 0.05). The maximum temporal difference in the rainy season reached 1–2 months; (2) The mutations of precipitation in the period of pre-flood (PP), precipitation in the period of post-flood (PN), and long-cycle drought-flood abrupt transition index (LDFAI) in sub-basins of the YRB (e.g., Mintuojiang River Basin [MRB], Wujiang River Basin [WRB], Dongting Lake Basin [DLRB], Yichang-Hukou Reach [YC-HK], Downstream of Hukou [DHKRB], and Taihu Lake Basin [TLRB]) were prominent from 2001 to 2011; (3) both the single factor (i.e., meteorological factors or teleconnection index) and multiple factors (i.e., meteorological factors and teleconnection index) influenced the LDFAI of each sub-basin in the YRB. Related research is important and useful for studying dry–wet changes and water security issues in the YRB.
The study of river flow trends in water management and irrigation and water management is an important issue. In addition, monthly, seasonal and annual discharge trends of Karkheh watershed were evaluated using non-parametric Mann-Kendall tests, Sen's slope estimator and regression analysis. Inverse distance weighting method was also used to study the spatial variation of discharge trends in Karkheh watershed. Accordingly, discharge data from eleven wells of the above-mentioned basin for the period 1990 to 2018 were used. The results of this study showed that Dubai has had annual rainfall at all of these stations, except for Mir-Sayed Ali. The values of this major are Hamidieh, Pai Pol, Pol Zal, Poldokhtar, Afrin, Cham Fig, Noorabad, Doab Merak, Kakarza and Pulchehr, respectively, 48, 33, 16, 5, 15, 4, 0.4, 1.4. It decreased by 2.6 and 13 cubic meters, while it increased by 0.4 cubic meters at the Sarab Ali station. Based on the findings of the study, applying nonparametric Mann-Kendall method and age in trend analysis of monthly, seasonal and annual discharge series have shown that the performance of these two tests are similar at times and when the frequency of duplicate data is high, the age method can be answered. More realistic than Mann-Kendall's approach, this approach can be applied to future water, water planning and management.
Renewable sources of electricity, such as solar and wind, need to be paired with sources of reliable baseload. Hydropower is a renewable, low‐emission source of electricity baseload available throughout much of the world as an alternative to electricity conventionally provided by thermal combustion of fossil fuels; however, the global hydropower sector as it stands relies upon surface water flows of substantial and predictable volume. This makes it vulnerable to climate change. The impact of climate change on the hydropower sector is difficult to predict, and not globally uniform. It might be positive, negative, or inconsequential depending upon the local timing and magnitude of changes, reservoir size, allocation priority, and the energy market. The secondary effects of climate change on glacier lake outbursts floods, landslides, and sediment load are poorly understood. In addition, when planning hydropower projects for the future, attention must be given to the greenhouse gas contribution of the impounded waters behind storage dams, and the impact of dams on water temperature. In the past decade, sovereign nations and international development agencies worldwide have evaluated the potential of hydropower as a cost‐effective, clean, sustainable option for baseload electricity supply. There is therefore a crucial need to assess the opportunities and risks hydropower poses across a wide range of potential future climate conditions. This review paper conducts a global survey of the literature on the effect of climate change on hydropower and identifies room for improvement in current approaches to evaluation of the net benefits of hydropower projects under climate change.
This article is categorized under: Vulnerability and Adaptation to Climate Change > Learning from Cases and Analogies
Assessing Impacts of Climate Change > Evaluating Future Impacts of Climate Change
Understanding hydro-climatic trends in space and time is crucial for water resource planning and management, agricultural productivity and climate change mitigation of a region. This study examined the spatiotemporal variations in precipitation, reference evapotranspiration (ETo) and streamflow in a tropical watershed located in the central highlands of Ethiopia. Temporal trend implications were analyzed using the Mann-Kendall test, and Theil-Sen approach, whereas the inverse distance weighted interpolation method was applied for spatial trend variability analysis. The result showed that a significant decreasing trends in streamflow for the major rainy (Kiremt: Jun - Sept) season and annual time scales. At the same time, the annual and monthly ETo followed significantly increasing trends, but there has been a trendless time series for most of the months and annual mean precipitation series for the period 1986 - 2015. The study indicated that the spatial variability of annual and seasonal precipitation series decreased from north to south and west to east, while this was increased for ETo both for annual and seasonal time series over the study watershed. The contribution of rainfall and mean temperature to streamflow decline was insignificant. It is pointed out that river flow regime is weakly affected by climate changes, hence human activities are stronger in explaining the river flow trends of the watershed. Therefore, urgent calls on the needs for reducing human-induced impacts, and implementing appropriate watershed management, conservation measures and an efficient use of water resources.
Expected increases in extreme rainfall events due to global warming could lead to increased soil erosion in mountainous areas. In order to study this impact on specific areas, the present study identified the spatiotemporal variation of erosive rainfall and the influence of its variation on streamflow and sediment discharge within the Ganjiang River Basin. Daily average rainfall data were obtained from 23 national meteorological observation stations along with streamflow and sediment concentration data collected for 1964-2013 at 6 control stations. The nonparametric Mann-Kendall method and Pettitt test were used for trend analysis and change-point detection, and the modified double mass curve method was used to quantify the effects of both erosive rainfall variation and human activities on hydrological regime shifts. Results showed significant monthly variation in erosive rainfall and significant increases in rainstorms over the entire watershed, particularly in the downstream subzone and northeast corner of the upstream subzone. While moderate rain showed an insignificant decrease in both subzones and the entire watershed, heavy rain showed no significant variation over the entire watershed but did show a significant increase in both the midstream and downstream subzones. The changes in accumulative erosive rainfall had only small effects on reduction in sediment discharge after the change-point year. In contrast, human activities contributed to more than 50% of the changes in sediment discharge in the entire basin. These findings provide a research basis for the study of extreme climate, flood disaster prevention, and soil erosion prediction over the entire watershed.
Nas regiões litorâneas os ambientes inundáveis ocorrem no baixo curso dos rios e de seus afluentes, onde o ciclo diário de inundação comandado por marés resulta em condições hidrodinâmicas de considerável complexidade. Na costa norte do Brasil, na adjacência do Sistema Tocantins-Maratauíra (STM), estuário do Rio Pará, os ambientes inundáveis reúnem características físicas que incluem uma geografia insular de retaguarda continental, intensa descarga fluvial e um regime de marés com amplitude de até 6 m. A fim de compreender como os ambientes inundáveis desse estuário são afetados por marés, este trabalho se apoia em abordagem multi-proxy (hidrodinâmica, topografia, vegetação, morfologia e cobertura sedimentar superficial) para a delimitação do estuário do rio Pará em zonas e para a investigação dos ambientes inundáveis do STM, relacionando-os à zona estuarina correspondente. Baseado nos resultados alcançados, três ambientes inundáveis e um não inundável foram reconhecidos. Esses ambientes integram o Estuário Superior do Rio Pará e têm seu ciclo de inundação regido por mesomarés. Por outro lado, devido à alta descarga fluvial, a paisagem ecológica é constituída essencialmente por ecossistemas de água doce. Os resultados revelam que os ambientes mais suscetíveis à inundação se situam no intervalo entre 0 e 3 m e representam 39% do complexo insular. Paradoxalmente, a maior ocorrência destes ambientes inundáveis é no setor sul (40,6%), direcionado ao continente, realçando a natureza dinâmica e mais instável desse setor em relação ao setor norte (21,1%), direcionado ao mar. As evidências mostram ainda que a maré representa uma das principais forçantes indutoras da hidrodinâmica local, tornando os cursos integrados à rede de drenagem do STM compatíveis com a designação de rios de maré. Os resultados proveem melhor compreensão acerca da morfodinâmica da paisagem moderna e, ao mesmo tempo, expõem sua vulnerabilidade, tendo em vista sua ocupação humana.
This study evaluated the performance of clear sky surface solar radiation (SSR) and its long-term evolution mechanism in the second Modern-Era Retrospective Analysis for Research and Applications (MERRA-2) in East Asia. The results revealed that although MERRA-2 overestimated the clearness index and clear sky SSR, the reanalysis performed well in northwestern, northern, northeastern, and central East Asia. From 1980 to 2019, clear sky SSRs decreased significantly in most areas. Aerosols play a dominant role in the annual variation of clear sky SSR rather than water vapor. In northwestern East Asia, owing to the influence of the increase in aerosol optical depth (AOD), the clear sky SSR showed a strong downward trend during 1993–2013. After 2007, the increase in water vapor played an important role in the weakening of the clear sky SSR. In northern, northeastern, and central East Asia, clear sky SSRs ushered in a brightening stage at the beginning of the 21st century because of the reduction in AOD. The magnitude of the change in Central East Asia is even more pronounced. In the Tarim Basin and northwestern India, dust plays an important role in the variation of clear sky SSR, whereas anthropogenic aerosols drive clear sky SSR in highly industrialized regions.
Base flow is an important component of flow hydrograph which originated from groundwater flow reserves. The aim of this study was to compare graphically and recursive digital filtering techniques in base flow separation and selection of appropriate methods to estimate the base flow contribution in number of rivers over Ardebil Province. Also, temporal changes of base flow and surface runoff through months of the year were analyzed in a 22-year period from 1389 to 1368 over 22 watersheds in the Ardabil Province is another aim of this study. Therefore, the performance graphical methods, and digital filtering techniques, were evaluated in base flow separation. The comparison of separated base flow amounts with recession analysis method indicates that the One-parameter algorithm was the best method in separation of base flow, was used to estimate the base flow contribution through the studied stations. Then the average values of total runoff and base flow were calculated in different seasonal changes of base flow were prepared.The low amount of base flow were observed in the Eastern part of the study area, while the West and Southwest parts of the Ardabil Provinces had the highest base flow component, as well as the maximum amount of the base flow is related to the three months of the spring season. It should be noted that the highest base flow amount were observed in summer season in the Hir, Sola, and Iril stations, the potential variations in the surface runoff and base flow components through seasons in different watersheds.
Determination of the Precipitation Regime and the Seasonality Index Variations in the Central Part of the Ardabil Province Precipitation is the most important climatic factor, particularly in dry lands and its regime characteristics is affected by the change in climate. The precipitation regime is a result of physical, spatial and temporal interactions. The seasonality index (SI) specifies the distribution of monthly rainfall over the year and evaluates the seasonal variations of the rainfall regime. The present study was conducted to determine the precipitation regime and to detect the trend of precipitation SI at the central part of the Province of Ardabil. The rainfall data of 24 stations were collected for the 1989–2012 period. Descriptive statistics of monthly precipitation data were presented both graphically and statistically, and the spatial-temporal variations were estimated using the SI and coefficient of variation (CV). The trend of precipitation SI at different rain gauge stations was determined using the Mann-Kendall test. The results showed that the highest CV belonged to the Sad-Ghorichay and Lay Stations (65 and 63%), and the lowest was related to the Shamsir Khani Station (36%). Based on the precipitation SI of monthly data, two main regimes were determined: a short dry-season (SI= 0.2–0.3), and a wet-season having the SI value of 0.6. The results of the Mann-Kendall test showed that most stations had either negative or positive trends in the precipitation SI. The increasing trend in the study area was more than the decreasing trend; only in some stations was the trend statistically significant. Also, assessing the CV of precipitation data showed that the uniformity of monthly precipitation values had decreased during the study period. Increasing the CV and precipitation SI indicate a change in precipitation regime; consequently, an increase in the severity of possible droughts in the study area.
Investigation of the process sedimentology of mouth bar deposition demonstrates a link to the seasonality associated with abrupt climate warming events during the early Eocene. While a relationship between fluvial sedimentology and climate events has been established previously, such documentation within mouth bar deposits is missing. Deltaic mouth bars of the Douglas Creek Member of the Green River Formation in the Uinta Basin record a fluvial–lacustrine response to abrupt warming events associated with the Early Eocene Climatic Optimum. This study ties the observed sedimentology of these mouth bars and their deposition via hyperpycnal currents to these climatic events. Detailed measured sections and analysis of stratigraphic architecture of outcrops in the eastern Uinta Basin document the sedimentology and stratigraphy of delta mouth bar complexes. Internal structures include climbing ripple cross‐lamination, convolute bedding, and those associated with transitional to upper flow regime bedforms such as planar laminations with normal grading and convex upward stratifications. The dominance of upper flow regime bedforms as well as interpreted long run out distances suggests that density currents deposited mouth bars tens of kilometres from the shoreline under Froude supercritical flow conditions. The highly seasonal climate regime of the early Eocene, capable of producing high‐sediment yield flooding events, likely provided the mechanism for hyperpycnal current formation within a relatively freshwater lake and controlled the timing of mouth bar deposition. Discrete lacustrine carbonate‐dominated packages separate periods of episodic fluvial discharge, recording reduced fluvial deposition between warming events. The established link between the occurrence of upper flow regime bedforms and the timing of climate warming events suggests that these climate conditions may be important for their formation and preservation. The study has implications for expanding existing mouth bar depositional models to include climatically controlled upper flow regime bedforms.
Although El Niño-Southern Oscillation (ENSO) has been widely confirmed to have significant impacts on climate change in Asia, it is unknown whether the climate change in the Yangtze River Basin (YTR basin) is related to the operation of the Three Gorges Reservoir, which is the world’s largest hydropower station. In this study, we used the Standardized Precipitation Evapotranspiration Index (SPEI) as an indicator of climate change and found that the mutation period of the YTR basin was 2003–2006 based on three mutation tests. By analyzing the trends of the SPEI and five related meteorological factors before and after 2003, it was found that the construction of the Three Gorges Reservoir increased the relative humidity and provided a more humid climate for the downstream basin. The relationships between drought events and ENSO and the water level of the reservoir indicated that the basin was more prone to drought in El Niño years and the Three Gorges Reservoir could alleviate agricultural drought in the downstream basin. The spatial impacts of the Three Gorges Reservoir on regional climate change were more pronounced, while the impact of ENSO could not be reflected at the station scale.
The Asian monsoon and associated river systems supply the water that sustains a large portion of humanity, and has enabled Asia to become home to some of the oldest and most productive farming systems on Earth. This book uses climate data and environmental models to provide a detailed review of variations in the Asian monsoon since the mid-Holocene, and its impacts on farming systems and human settlement. Future changes to the monsoon due to anthropogenically-driven global warming are also discussed. Faced with greater rainfall and more cyclones in South Asia, as well as drying in North China and regional rising sea levels, understanding how humans have developed resilient strategies in the past to climate variations is critical. Containing important implications for the large populations and booming economies in the Indo-Pacific region, this book is an important resource for researchers and graduate students studying the climate, environmental history, agronomy and archaeology of Asia.
The Asian monsoon and associated river systems supply the water that sustains a large portion of humanity, and has enabled Asia to become home to some of the oldest and most productive farming systems on Earth. This book uses climate data and environmental models to provide a detailed review of variations in the Asian monsoon since the mid-Holocene, and its impacts on farming systems and human settlement. Future changes to the monsoon due to anthropogenically-driven global warming are also discussed. Faced with greater rainfall and more cyclones in South Asia, as well as drying in North China and regional rising sea levels, understanding how humans have developed resilient strategies in the past to climate variations is critical. Containing important implications for the large populations and booming economies in the Indo-Pacific region, this book is an important resource for researchers and graduate students studying the climate, environmental history, agronomy and archaeology of Asia.
The upper reaches of the Hanjiang River Basin (HM-CSNWTP) is the headwater source for the middle route of China's South-to-North Water Transfer Project (M-CSNWTP), as well as the north-south transitional zone of central China, and is characterized by high precipitation sensitivity and variability. Changes in precipitation patterns can affect the potential runoff generation capacity of the HM-CSNWTP. Therefore, this study was focused on exploring the dynamic precipitation patterns over the HM-CSNWTP and the potential runoff generation capacity of this region at annual and seasonal timescales. Daily precipitation data from 34 meteorological stations for the period 1961–2016 were collected in order to estimate 4 categories of rainfall indices: average daily precipitation on all days (ADP) and on rainy days (ARP), total amount (TP), and rainy days (TD). The non-parametric Mann-Kendall test, LOWESS smoothing, and collaborative kriging method were implemented. The statistical results indicated that: (1) The annual ADP over the basin decreased slightly, at the rate of −0.22%/10a (−0.002 mm/d/a). Seasonally, summer ADP increased by 1.4%/10a (0.005 mm/d/a), while decreasing ADP values were detected in other seasons. Large increases in annual and summer ARP were found, at rates of 3.73%/10a (0.018 mm/d/a) and 3.72%/10a (0.039 mm/d/a), over the HM-CSNWTP, mainly in the southwestern area (Region III), due to the large changes of annual and summer ARP. Annual and summer ARP increased at significant rates of 7.22%/10a (0.034 mm/d/a) and 10.64%/10a (0.083 mm/d/a), respectively. (2) Decreasing light rainfall amounts (TP0-10) and days (TD0-10), and increasing heavy rainfall amounts (TP>25) and days (TD>25) were detected over the HM-CSNWTP, especially for Region III, in which TP>25 and TD>25 increased by 7.00%/10a (1.076 mm/a) and 5.37%/10a (0.023 d/a), respectively. (3) In the wettest assumption scenario, the estimated annual, spring, summer, autumn, and winter runoff depths were 912.9 mm, 183.0 mm, 410.6 mm, 259.0 mm, and 60.3 mm, respectively. In the driest assumption, the estimated annual, spring, summer, autumn, and winter runoff depths were 131.4 mm, 35.6 mm, 65.7 mm, 27.8 mm, and 2.3 mm, respectively, and the planned diversion water accounted for 76.1%, 63.2%, 70.0%, 102.2%, and 156.5% of the annual and seasonal driest assumption runoff depths, respectively. Thus, the water diversion of the M-CSNWTP in the driest assumption may trigger water shortages and environmental disasters in the lower reaches of the Hanjiang River Basin, especially at annual, autumn, and winter timescales. These findings provide some basic information for local water resource management in the HM-CSNWTP.
The Asian monsoon and associated river systems supply the water that sustains a large portion of humanity, and has enabled Asia to become home to some of the oldest and most productive farming systems on Earth. This book uses climate data and environmental models to provide a detailed review of variations in the Asian monsoon since the mid-Holocene, and its impacts on farming systems and human settlement. Future changes to the monsoon due to anthropogenically-driven global warming are also discussed. Faced with greater rainfall and more cyclones in South Asia, as well as drying in North China and regional rising sea levels, understanding how humans have developed resilient strategies in the past to climate variations is critical. Containing important implications for the large populations and booming economies in the Indo-Pacific region, this book is an important resource for researchers and graduate students studying the climate, environmental history, agronomy and archaeology of Asia.
Twentieth century trends of precipitation are examined by a variety of methods to more fully describe how precipitation has changed or varied. Since 1910, precipitation has increased by about 10% across the contiguous United States. The increase in precipitation is reflected primarily in the heavy and extreme daily precipitation events. For example, over half (53%) of the total increase of precipitation is due to positive trends in the upper 10 percentiles of the precipitation distribution. These trends are highly significant, both practically and statistically. The increase has arisen for two reasons. First, an increase in the frequency of days with precipitation ]6 days (100 yr)1[ has occurred for all categories of precipitation amount. Second, for the extremely heavy precipitation events, an increase in the intensity of the events is also significantly contributing (about half) to the precipitation increase. As a result, there is a significant trend in much of the United States of the highest daily year-month precipitation amount, but with no systematic national trend of the median precipitation amount.These data suggest that the precipitation regimes in the United States are changing disproportionately across the precipitation distribution. The proportion of total precipitation derived from extreme and heavy events is increasing relative to more moderate events. These changes have an impact on the area of the United States affected by a much above-normal (upper 10 percentile) proportion of precipitation derived from very heavy precipitation events, for example, daily precipitation events exceeding 50.8 mm (2 in.).
This study attempts to combine four independent long-term climatic data and modern observations into one cohesive set; to describe the spatial and temporal patterns of variability of dry and wet periods in East Asia over the past one thousand years; and to examine physical causes of the pattern variations. The data include the 220-year observed precipitation in Seoul, South Korea, the dryness-wetness intensity data in eastern China for the last 530 years, and other two independent chronologies of dryness-wetness grades in the past millennium in eastern China based on instrumental observations and historical documents. Various analysis methods including wavelet transform and rotated empirical orthogonal function were used in revealing climate variations from these datasets. Major results show that the dry and wet anomalies initially appeared in the north part of eastern China and then migrated southward to affect south China. This process is repeated about every 70 years. However, in contrast in the last two decades of the twentieth century a dry situation appeared in north China and a wet climate predominated in the south part of the country. The multidecadal variations of the monsoon circulation in East Asia and the thermal contrast between inland Asia and its surrounding oceans may contribute to the dry-wet phase alternation or the migration of dry-wet anomalies. In regional scale variations, a consistent dry or wet pattern was observed spreading from the lower Yangtze River valley to South Korea. Frequencies of severe dry-wet situations were low in the eighteenth and nineteenth century and they were higher in the twentieth century. The recent increasing trend in frequencies of severe dry-wet chances occurred along with global warming and regional climatic changes in China.
Various methods are available to estimate reference evapotranspiration (ET0) from standard meteorological observations. The Penman-Monteith method is considered to be the most physical and reliable method and is often used as a standard to verify other empirical methods. This study estimates and compares the monthly ET0 calculated by 3 methods at 580 Chinese stations over the last 50 yr. The Penman-Monteith method is used here as a reference, and its spatial and temporal differences with the Thornthwaite method and pan measurement are evaluated. The results show that: (1) in terms of spatial difference, the Thornthwaite estimates show different regional patterns, while pan measurements display a consistent regional pattern; (2) the temporal variability of ET0 is much better represented by pan measurements than by the Thornthwaite estimates. Overall, pan measurements are more useful than the Thornthwaite estimates if appropriate pan coefficients are determined. The Thornthwaite method only considers the temperature and latitude and gives unreliable results under dry conditions, e.g. in NW China. With reference to the Penman-Monteith estimates, the correction factors (pan coefficients) of pan measurements for the whole of China, and the regional averages over the 10 major drainage basins are determined. The average value lies between 0.6 and 0.8, although a seasonal and regional difference is present.
A framework is presented to quantify observed changes in climate within the contiguous United States through the development and analysis of two indices of climate change, a Climate Extremes Index (CEI) and a U.S. Greenhouse Climate Response Index (GCRI). The CEI is based on an aggregate set of conventional climate extreme indicators, and the GCRI is composed of indicators that measure changes in the climate of the United States that have been projected to occur as a result of increased emissions of greenhouse gases. The CEI supports the notion that the climate of the United States has become more extreme in recent decades, yet the magnitude and persistence of the changes are not large enough at this point to conclude that the increase in extremes reflects a nonstationary climate. Nonetheless, if impacts due to extreme events rise exponentially with the index, then the increase may be quite significant in a practical sense. Similarly, the positive trend of the U.S. GCRI during the twentieth century is consistent with an enhanced greenhouse effect. The increase is unlikely to have arisen due to chance alone (there is about a 5% chance). Still, the increase of the GCRI is not large enough to unequivocally reject the possibility that the increase in the GCRI and anticipated changes says little about the sensitivity of the climate system to the greenhouse effect. Both indices increased rather abruptly during the 1970s, a time of major circulation changes over the Pacific Ocean and North America. 37 refs., 14 figs., 4 tabs.
This article describes investigationsinto the effects of climate change on flow regimes oftwenty-five catchments (from 6 to 1293 km2) incentral Sweden. Hydrological responses of fifteenhypothetical climate change scenarios (e.g.combinations of T = +1, +2 and +4 C andP = 0, 10%, 20%) were simulated by a conceptual monthly water balance model. The results suggest thatall the hypothetical climate change scenarios wouldcause major decreases in winter snow accumulation.Significant increase of winter flow and decrease ofspring and summer runoff were resulted from mostscenarios. Attendant changes in actualevapotranspiration were also examined for all climatechange scenarios. Despite the changes in seasonaldistribution of evapotranspiration, the change inannual total evapotranspiration was relatively smallwith the maximum change of 23% compared with the 76%for mean annual snow water equivalent changes and 52%for mean annual runoff changes. Such hydrologicresults would have significant implications on futurewater resources design and management.
Changes in China’s temperature and precipitation extremes have been studied by using observational data after 1950. The results reveal that mean minimum temperature has increased significantly in China during the past 40 years, especially in the winter in northern China. Meanwhile, nation-wide cold wave activity has weakened and the frequency of cold days in northern China has been reduced significantly. Mean maximum temperatures display no statistically significant trend for China as a whole. However, decreasing summer mean maximum temperatures are obvious in eastern China, where the number of hot days has been reduced. Seasonal 1-day extreme maximum temperatures mainly reflect decreasing trends, while seasonal 1-day extreme minimum temperatures are increasing.
A statistically significant reduction of much above normal rain days in China has been detected. Contrarily, an increasing trend was detected in much above normal of precipitation intensity (precipitation/number of precipitation days) during the past 45 years.
A simple statistical model of daily precipitation based on the gamma distribution is applied to summer (JJA in Northern Hemisphere, DJF in Southern Hemisphere) data from eight countries: Canada, the United States, Mexico, the former Soviet Union, China, Australia, Norway, and Poland. These constitute more than 40% of the global land mass, and more than 80% of the extratropical land area. It is shown that the shape parameter of this distribution remains relatively stable, while the scale parameter is most variable spatially and temporally. This implies that the changes in mean monthly precipitation totals tend to have the most influence on the heavy precipitation rates in these countries. Observations show that in each country under consideration (except China), mean summer precipitation has increased by at least 5% in the past century. In the USA, Norway, and Australia the frequency of summer precipitation events has also increased, but there is little evidence of such increases in any of the countries considered during the past fifty years. A scenario is considered, whereby mean summer precipitation increases by 5% with no change in the number of days with precipitation or the shape parameter. When applied in the statistical model, the probability of daily precipitation exceeding 25.4 mm (1 inch) in northern countries (Canada, Norway, Russia, and Poland) or 50.8 mm (2 inches) in mid-latitude countries (the USA, Mexico, China, and Australia) increases by about 20% (nearly four times the increase in mean). The contribution of heavy rains (above these thresholds) to the total 5% increase of precipitation is disproportionally high (up to 50%), while heavy rain usually constitutes a significantly smaller fraction of the precipitation events and totals in extratropical regions (but up to 40% in the tropics, e.g., in southern Mexico). Scenarios with moderate changes in the number of days with precipitation coupled with changes in the scale parameter were also investigated and found to produce smaller increases in heavy rainfall but still support the above conclusions. These scenarios give changes in heavy rainfall which are comparable to those observed and are consistent with the greenhouse-gas-induced increases in heavy precipitation simulated by some climate models for the next century. In regions with adequate data coverage such as the eastern two-thirds of contiguous United States, Norway, eastern Australia, and the European part of the former USSR, the statistical model helps to explain the disproportionate high changes in heavy precipitation which have been observed.
Monthly precipitation trends of 160 stations in China from 1951–2002 have been analysed and interpolated. The Mann-Kendall trend test was applied to examine the monthly precipitation data. Significant positive and negative trends at the 90, 95, and 99 percent confidence levels were detected for numerous stations. The number, distribution, and direction of the trends varied from month to month.
The detected trends were spatially interpolated by applying the Inverse Distance Weighted (IDW) interpolation method. The spatial presentation of the detected precipitation trends gives a better understanding of climatic changes or variations in China during the last 50 years. This is especially the case for highlighting the spatial structure of precipitation trends.
A clustering of trends is observed in certain months, including distinct trend belts especially in east and north-east China. Nevertheless, positive as well as negative monthly trends can be noted simultaneously in different areas. The spatial interpolation of precipitation trend analysis results is a useful approach to give further understanding of the regional pattern of precipitation trends in China.
Ongoing global climatic change initiated by the anthropogenic release of carbon dioxide is a matter of intense debate. We focus both on the impact of these climatic changes on the global hydrological cycle and on the amplitude of the increase of global and continental runoff over the last century, in relation to measured temperature increases. In this contribution, we propose an original statistical wavelet-based method for the reconstruction of the monthly discharges of worldwide largest rivers. This method provides a data-based approximation of the evolution of the annual continental and global runoffs over the last century. A consistent correlation is highlighted between global annual temperature and runoff, suggesting a 4% global runoff increase by 1 °C global temperature rise. However, this global trend should be qualified at the regional scale where both increasing and decreasing trends are identified. North America runoffs appear to be the most sensitive to the recent climatic changes. Finally, this contribution provides the first experimental data-based evidence demonstrating the link between the global warming and the intensification of the global hydrological cycle. This corresponds to more intense evaporation over oceans coupled to continental precipitation increase or continental evaporation decrease. This process finally leads to an increase of the global continental runoff.
Precipitation trends in China with special emphasis on the Yangtze catchment area have been analysed. Significant positive and negative trends for the second half of last century have been detected for different regions on a monthly scale. The interpolation of the trends lead to characteristic spatial trend patterns in China. The analysis of long-term precipitation records in the Yangtze catch-ment area revealed a concentration of summer precipitation within a shorter period of time on the monthly scale and a distinct cyclicity for some stations on the annual scale.
The summer rainfall over the middle-lower valley of the Yangtze River and over the whole eastern China experienced a notable regime shift in about 1979. This change is consistent with a simultaneous jump-like change in the 500 hPa geopotential height (Phi500) over the northern Pacific. The rainfall over the Yangtze River valley is closely related to the Phi500 averaged over the area 20°-25°N, 125°-140°E, with a correlation coefficient of 0.66 for the period 1958-1999. Since 1980, the subtropical northwestern Pacific high (SNPH) has enlarged, intensified, and extended southwestward. The changes in the SNPH are strongly associated with the variations of the sea surface temperatures (SSTs) of the eastern tropical Pacific and tropical Indian Ocean. The anomalies of these SSTs, responsible primarily for the shift of the summer rainfall over the Yangtze River through the changes in SNPH, precede the Phi500 signals with different leading times.
In the middle reaches of the Yangtze River, the floods have become more and more frequent, and the water level rises higher than before. The damages are becoming ever more serious. This is primarily a consequence of human activity in the river basin. Three aspects deserve particular attention. First, destruction of vegetation has led to soil erosion in the upper reaches. In the past 30 years, the forest cover has been reduced to half, while the area exposed to severe erosion doubled in size. In the long run, this can be expected to increase flooding. Second, land reclamation and siltation has reduced lake sizes. This has resulted in decrease of the flood storage capacity. Third, the construction of levees has caused flood levels to rise due to restricted flood discharge capacity. Establishment of the Great Jinjiang levee caused silting up of the riverbed and valley in the mid-reaches of Yangtze. Consequently, the discharge capacity decreased to 60,000–68,000 m3/s, which is sufficient only for ordinary floods. This article concludes that the deteriorating flood situation is the result of inappropriate human intervention in the natural environment. It is suggested that the appropriate strategy should change from “keeping the flood away” to “giving the flood way”. Related tactics and strategies under consideration are briefly summarized.
An extended period of wetter weather persisted over the Yangtze river region for three months in 1998 and culminated with a series of intense storms, causing the worst floods of this century. The present analysis shows that the flow was only a 60-year event according to the maximum discharge peak. Human-induced deforestation and soil erosion play an important role in the special phenomena of the low peak charge but highest water level in the 1998 flood. Thus, to control flooding, soil and water conservation should be implemented on a large scale in this river region.
Recent studies on changes in precipitation intensity encompassing North America have found evidence for an increase in the relative amount of precipitation contributed by heavy and extreme rainfall events in the last 80 years. Within this context, the purpose of this paper is to verify whether such a signal can also be detected in northern Italy, where daily precipitation data are available from the beginning of the 19th century. The analysis is performed by applying the non-parametric Mann–Kendall test to mean anomaly series obtained through averaging the anomalies of some precipitation intensity statistics over five stations: Genoa (1833–1998), Milan (1858–1998), Mantova (1868–1997), Bologna (1879–1998) and Ferrara (1879–1996). It provides evidence that in northern Italy, the number of rainy days has a stronger and more significant negative trend than the corresponding precipitation amount, both on a yearly basis and in all of the seasons. As a consequence, precipitation intensity has a positive trend. The increase in precipitation intensity causes a significant positive trend in the proportion of total precipitation contributed by heavy precipitation events (i.e. daily precipitation >25 mm and daily precipitation >50 mm). The trend is mainly caused by the last 60–80 years, and is particularly evident in the periods of 1930–1945 and 1975–1995. The increase in precipitation intensity is connected to a modification of the distribution of daily precipitation values in a year, with trends that grow from the lower to the upper percentiles, and up to 4 mm/100 years for the 95th percentile. Copyright © 2000 Royal Meteorological Society
Identifying and removing the influence of atmospheric circulation variability on central England temperature increases the statistical significance of warming trends in spring, autumn and the annual mean over the last 50 years. The trends are more detectable because the circulation changes contribute greatly to the ‘noise’ of interannual to interdecadal variability, but induce only small multi-decadal trends (the ‘signal’). Factoring out the circulation can thus enhance the signal-to-noise ratio. For precipitation, the recent enhancement in the difference between summer rainfall in south-east England and winter precipitation in northern Scotland can partly be explained by atmospheric circulation variability over the past 40 years (particularly the increase in the North Atlantic Oscillation index from the 1960s to the early 1990s). Copyright © 2000 Royal Meteorological Society.
This paper explores the potential implications of climate change for the use and management of water resources in Britain. It is based on a review of simulations of changes in river flows, groundwater recharge and river water quality. These simulations imply, under feasible climate change scenarios, that annual, winter and summer runoff will decrease in southern Britain, groundwater recharge will be reduced and that water quality – as characterised by nitrate concentrations and dissolved oxygen contents – will deteriorate. In northern Britain, river flows are likely to increase throughout the year, particularly in winter. Climate change may lead to increased demands for water, over and above that increase which is forecast for non-climatic reasons, primarily due to increased use for garden watering. These increased pressures on the water resource base will impact not only upon the reliability of water supplies, but also upon navigation, aquatic ecosystems, recreation and power generation, and will have implications for water quality management. Flood risk is likely to increase, implying a reduction in standards of flood protection. The paper discusses adaptation options.
This paper concerns the impact of human-induced global climate change on the River Rhine discharge. For this purpose a model for climate assessment, named ESCAPE, is coupled to a water balance model, named RHINEFLOW. From climate scenarios, changes in regional annual water availability and seasonal discharge in the River Rhine Basin are estimated. The climate scenarios are based on greenhouse gases emissions scenarios. An assessment is made for ‘best guess’ seasonal discharge changes and for changes in frequencies of low and high discharges in the downstream reaches of the river. In addition, a quantitative estimation of the uncertainties associated with this guess is arrived at.
The results show that the extent and range of uncertainty is large with respect to the ‘best guess’ changes. The uncertainty range is 2–3 times larger for the Business-as-Usual than for the Accelerated Policies scenarios. This large range stems from the doubtful precipitation simulations from the present General Circulation Models. This scenario study showed the precipitation scenarios to be the key-elements within the present range of reliable climate change scenarios.
For the River Rhine ‘best guess’ changes for annual water availability are small according to both scenarios. The river changes from a present combined snow-melt-rain fed river to an almost entirely rain fed river. The difference between present-day large average discharge in winter and the small average discharge in autumn should increase for all scenarios. This trend is largest in the Alpine part of the basin. Here, winter discharges should increase even for scenarios forecasting annual precipitation decreases. Summer discharge should decrease. ‘Best guess’ scenarios should lead to increased frequencies of both low and high flow events in the downstream (Dutch) part of the river. The results indicate changes could be larger than presently assumed in ‘worst case scenarios’ used by the Dutch water management authorities.
The Czech Republic has a northern hemisphere Atlantic-continental type of moderate climate. Mean annual temperature ranges between 1.0 and 9.4 C (between 8.8 and 18.5 C in summer and between –6.8 and 0.2 C in winter). Annual precipitation ranges between 450 mm in dry regions and 1300 mm in mountainous regions of the country. With its 2000 m3 per capita fresh water availability, the Czech Republic is slightly below average. Occasional water shortages do not usually result from general unavailability of water resources but rather from time or space variability of water supply/demand and high degree of water resources exploitation. To study potential impacts of climate change on hydrological system and water resources, four river basins have been selected in the territory of the Czech Republic: the Elbe River at Decin (50761.7 km2), the Zelivka River at Soutice (1188.6 km2), the Upa River at Ceska Skalice (460.7 km2) and the Metuje River at Marsov n. M. (93.9 km2). To simulate potential changes in runoff, three hydrological models have been applied using incremental and GCM (GISS, GFDL and CCCM) scenarios: the BILAN water balance model, the SACRAMENTO (SAC-SMA) conceptual model and the CLIRUN water balance model. The paper reviews methods applied in the study, results of the assessments and concludes with suggestions for possible general adaptation policy options where the preference is for nonstructural measures such as water conservation, efficient water demand management and protection of water resources.
The monthly, seasonal, and annual precipitation trends in the Yangtze river catchment have been detected through analysis
of 51 meteorological stations’ data between 1950–2002 provided by National Meteorological Administration. Results reveal that:
1) Summer precipitation in the Yangtze river catchment shows significant increasing tendency. The Poyanghu lake basin, Dongtinghu
lake basin and Taihu lake basin in the middle and lower reaches are the places showing significant positive trends. Summer
precipitation in the middle and lower reaches experienced an abrupt change in the year 1992; 2) The monthly precipitation
in months just adjoining to summer shows decreasing tendency in the Yangtze river catchment. The upper and middle reaches
in Jialingjiang river basin and Hanshui river basin are the places showing significant negative trends; 3) Extreme precipitation
events show an increasing tendency in most places, especially in the middle and lower reaches of the Yangtze river catchment.
The impact of a climate change scenario on regional climate conditions and runoff characteristics has been investigated for the Mulde catchment, a meso-scale sub-basin of the Elbe in Germany. First, the semi-distributed, conceptual model HBV-D has been successfully applied to simulate discharge for present climate conditions. Further, the expanded downscaling method (EDS) was calibrated and applied to observed global circulation fields in order to produce local climate input data for HBV-D. Finally, the coupled atmosphere-ocean model ECHAM4/OPYC3, driven by a climate change scenario, provided simulated global circulation patterns for application with EDS. The regionalised scenario conditions then served as input to HBV-D in order to investigate the impact of global climate change on regional hydrology. The results indicate that an obvious increase in temperature is accompanied by a clear tendency to reduced precipitation over the investigated area for the next 100 years. These conditions lead to a decrease in simulated mean discharges of the Mulde. The study is considered to be a contribution for regional impact studies on global climate change. At the same time, it demonstrates existing shortcomings and limitations of current climate impact research.
General Circulation Models simulate significant changes of temperature and precipitation over Europe as part of the anthropogenic climate change. In this study, the impacts of climate change on groundwater recharge and streamflow in a central European low mountain range catchment are investigated using a conceptual eco-hydrologic model, a revised version of the Soil and Water Assessment Tool (SWAT). To improve the reliability of our simulations, we compile plant physiological studies concerning the influence of elevated ambient CO2 concentrations on stomatal conductance and leaf area. Using this information to parameterise the model, we evaluate the impacts of two climate change scenarios, which represent a wide range of assumptions concerning future greenhouse gas emissions and climate sensitivity. The resulting effects on mean annual groundwater recharge and streamflow are small, as increased atmospheric CO2 levels reduce stomatal conductance thus counteracting increasing potential evapotranspiration induced by the temperature rise and decreasing precipitation. There are, however, more pronounced changes associated with the mean annual cycle of groundwater recharge and streamflow. Our results imply that due to the warming a smaller proportion of the winter precipitation will fall as snow. The spring snowmelt peak therefore is reduced while the flood risk in winter will probably increase. In summer, mean monthly groundwater recharge and streamflow are reduced by up to 50% potentially leading to problems concerning water quality, groundwater withdrawals and hydropower generation.
Hydrological records (covering a 100-year period) from the upper, middle and lower Yangtze River were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin. The Yangtze discharge, as expected, increases from the upper drainage basin downstream. Only an estimated 50% of the discharge is derived from the upper Yangtze, with the rest being derived from the numerous tributaries of the middle and lower course. However, the distribution of sediment load along the Yangtze is the reverse of that observed for discharge, with most of the sediment being derived from the upper basin. A dramatic reduction in sediment load (by ∼0.8×108 tons/year) occurs in the middle Yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper Yangtze rock sections. Considerable siltation also occurs in the middle Yangtze drainage basin as the river cuts through a large interior Dongting Lake system. Sediment load in the lower Yangtze, while significantly less than that of the upper river, is somewhat higher than the middle Yangtze because of additional load contributed by adjacent tributaries. A strong correlation exists between the discharge and sediment load along the Yangtze drainage basin during the dry season as lower flows carry lower sediment concentration. During the wet season, a strong correlation is also present in the upper Yangtze owing to the high flow velocity that suspends sand on the bed. However, a negative to poor correlation occurs in the middle and lower Yangtze because the flow velocity in these reaches is unable to keep sand in suspension, transporting only fine-grained particles downstream.
This paper describes the development and application of a procedure that identifies trends in hydrologic variables. The procedure utilizes the Mann–Kendall non-parametric test to detect trends, a permutation approach to estimate the test distribution, and accounts for the correlation structure in the data in determining the significance level of the test results. The research investigates 18 hydrologic variables that reflect different parts of the hydrologic cycle. The hydrologic variables are analyzed for a network of 248 Canadian catchments that are considered to reflect natural conditions. A selection of catchments identified to have trends in hydrologic variables is studied further to investigate the presence of trends in meteorological variables and the relationship between the hydrologic and the meteorological response to climatic change. It is concluded that a greater number of trends are observed than are expected to occur by chance. There are differences in the geographic location of significant trends in the hydrologic variables investigated implying that impacts are not spatially uniform.
Cumulative deviations from the mean are often used in the analysis of homogeneity. Features of five tests on the cumulative deviations are discussed. Some of these tests have optimal properties in testing the null hypothesis of homogeneity against a shift in the mean at an unknown point.Together with the classical von Neumann ratio the tests were applied to the annual amounts of 30-yr. rainfall records in The Netherlands. For a large number of records strong indications for a change in the mean were found. There were only small differences between the various test-statistics with respect to the number of records for which the null hypothesis was rejected.
Most previous investigations of the impact of potential climatic change on water supply systems have focused on individual systems so that their conclusions only apply to a particular system. Recent advances in computer technology, regional hydrology and our understanding of water supply system behavior allow for examination of the sensitivity of water supply system behavior to potential climatic change in a very general framework. A regional hydroclimatologic model of annual streamflow is developed for the northeastern United States which relates moments of annual streamflow to climatic and geomorphic characteristics at 166 gaging stations. The regional hydroclimatologic streamflow model is then combined with analytic relationships among water supply system storage, reliability, resilience and yield. The sensitivity of various water supply system performance indices such as yield, reliability and resilience are derived as a function of climatic, hydrologic and storage conditions. These results allow us to quantify, in general, the sensitivity of water supply system behavior to changes in the climatologic regime. Case studies for four watersheds in New York and one water supply system in Massachusetts indicate that our simple regional annual modelling approach can reproduce the results of much more detailed site-specific monthly hydroclimatologic modelling approaches.
Flood risk in the changing world—Yangtze floods Climate Change and Yangtze Floods
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The three-gorge project: its influence on the flood risks along the middle reaches of the Yangtze River and on the economy of the region surrounding the reservoir Climate Change and Yangtze Floods
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Flood characteristics of the Yangtze River and countermeasures for flood control Climate Change and Yangtze Floods
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Wang, J., 2005. Flood characteristics of the Yangtze River and countermeasures for flood control. In: Jiang, T., King, L., Gemmer, M., Kundzewicz, Z.W. (Eds.), Climate Change and Yangtze Floods. Science Press, Beijing, pp. 385–395.
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Historical Deluges of China
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Climate change in the East-Asian monsoon—introduction of a new method Fig. 13. Rainstorms and flood peaks of
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Climate change in the East-Asian monsoon—introduction of a new method of time series analysis
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The three-gorge project: its influence on the flood risks along the middle reaches of the Yangtze River and on the economy of the region surrounding the reservoir
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Flood risk in the changing world—Yangtze floods
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Evidence for global runoff increase related to climate warming
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