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Climate change poses critical threats to water related safety and sustainability in the Mekong River basin. Hydrological impact signals derived from CMIP3 climate change scenarios, however, are highly uncertain and largely ignore hydrological extremes. This paper provides one of the first hydrological impact assessments using the most recent CMIP5...
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... the original Global Land Cover 2000 data (GLC2000, 2003) into nine classes and then aggregated to the model's grid. The flow direction data was prepared from the SRTM90 m elevations ( Jarvis et al., 2008). The elevation data along the main river's branches was adjusted to force these branches into the proper flow direction. More detailed information on the model setup and its parameterization for the Mekong basin is available in Lauri et al. (2012 han, Pakse, Stung Treng and Kratie (Fig. 1). Observed discharge data was obtained from the Mekong River Commission's hydrological database (MRC, 2011b). Calibration and validation periods are 1981-1991 and 1991-2001, respectively. The hydrological model's performance was assessed using discharge plots and model performance in- dices. In particular, the daily river discharges plots and the flow duration curves (Vogel 5 and Fennessey, 1995) were used to visually check the goodness of fit between ob- served and simulated data. Furthermore, the Nash-Sutcliffe efficiency NSE (Nash and Sutcliffe, 1970) and relative biases indices were used to quantify the model's perfor- mance during calibration and validation. The Nash-Sutcliffe efficiency ranges between −∞ and 1, where values closer to 1 imply a better fit between observed and simulated We started the model calibration by using the initial parameterization from Lauri et al. (2012). Discharge simulation performance was further improved by adjusting several model's parameters. In particular, discharge amount and timing at key sta- tions were calibrated to better match with observed data by changing the two soil lay- 20 ers' depth and their water storage capacities. Vertical and horizontal infiltration rates were also adjusted to further improve simulations of high flows and low flows. Lastly, snowmelt rate and temperature thresholds for snow precipitation and snowmelt were adjusted to improve model performance at the upper catchment above Chiang Saen (Northern Thailand). All parameter values were adjusted within the physically realistic HESSD 12,2015 Mekong River flow and hydrological extremes under climate change ...
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... section presents changes in annual, seasonal and monthly river discharges under climate change. Annual changes are presented for all seven mainstream stations (see locations in Fig. 1) while we limit the rest of the results to three representative stations to maintain the paper's focus. These stations are Vientiane (Laos PDR), Mukdahan (Thailand) and Kratie (Cambodia), each representing the upper, middle and lower parts 20 of the basin, ...
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... Mekong ( Fig. 1) tropical monsoon climate ( Adamson et al., 2009;Renaud et al., 2012). Ele- vation in the basin ranges between above 5000 m in the Tibetan Plateau to only a few meters above sea level in the downstream river delta. The Mekong's hydrological regime is largely driven by monsoonal activities, most importantly the South-West Monsoon and to a lesser extent the North-East Monsoon (Costa-Cabral et al., 2007;MRC, 2009;Delgado et al., 2012). The South-East Mon- soon is dominant from May to September, whereas the North-East Monsoon is ac- tive from November to February. These monsoonal activities characterize the basin's hydrology into two hydrological seasons with distinctive flow characteristics. A sub- stantially larger proportion of the annual flow is generated during the wet seasons 10 (June-November). Depending on location, the wet season flow accounts for between 75 and 85 % of the total annual flow (calculated from MRC, 2005). Seasonal variation in river flow, especially the flood pulse occurring in the downstream deltas (i.e. the Tonle Sap Lake in Cambodia and the Mekong delta in Vietnam), supports a highly productive aquatic ecosystem and one of the world's major rice production area (Junk et al., 2006;15 Eastham et al., 2008;Hapuarachchi et al., ...
Citations
... In the lower section of the Mekong River, the two natural arms of the river (Tien River and Bassac Rivers) gradually separate into nine continuously functioning river beds, with a mean annual discharge 13,000 m3s [4]. In addition, the surface water system has been anthropogenically enriched with a network of canals, built over 3000 years of man settlement in this area [5]. There are two or three high water levels and ebbs in river branches and canal system of delta per day, with amplitude higher than 4 meters near sea area up to 1-2 m in Cambodia and Vietnam border region. ...
This work is licensed under Creative Commons Attribution 4.0 License AOMB.MS.ID.000571. Abstract Evaluation of short-time freshwater habitat fluctuations was provided in the period October 2019-February 2020 in the Mekong River delta in Vietnam. Three phases of water flow direction were documented in the diurnal tide cycle. In the middle-"stagnation" state, a daily maximal oxygen concentration in the river occurs, regardless of the sun's position above the horizon. Each tide cycle also creates a periodic water mass friction zone in the nearshore part of the riverbed and increases the sedimentation rate within the opposite direction of water mass flow. The biotic effects of freshwater habitat modification in the river branches are discussed.
... and 3-4% (RCP4.5) with an average of 3% across all scenarios (Hoang et al., 2016). The change patterns for the 95th and 99th percentile precipitation showed more prominent increases under Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) projections, though the change patterns for the 90th percentile precipitation were comparable to that of the annual precipitation (Wang et al., 2017). ...
... The temperature increase tends to be greater in the southern and northern parts of the basin, whereas the patterns for annual precipitation varied with GCMs and emission scenarios but increases were more likely in the Lancang River basin (Hoang et al., 2016;Lauri et al., 2012). Patterns for precipitation changes were different even under the same emission scenario: e.g., the largest increase was in the middle basin for three GCMs, while in the northernmost and southern parts for the remaining GCMs (Lauri et al., 2012). ...
... Patterns for precipitation changes were different even under the same emission scenario: e.g., the largest increase was in the middle basin for three GCMs, while in the northernmost and southern parts for the remaining GCMs (Lauri et al., 2012). Under CMIP5, precipitation was projected to increase in some areas while decrease in others, though the overall pattern was increasing (Hoang et al., 2016). ...
Droughts and floods are the main threats to the Lancang-Mekong River Basin (LMRB) . Drought mainly occurs during the dry season, especially in March and April, in the LMRB. The “dry gets drier” paradigm performs well in the LMRB, specifically in the Mekong Delta. Further, flood frequency and magnitude, which are determined by heavy rain, are also increasing in the LMRB. Droughts and floods show obvious seasonal and regional characteristics in the LMRB . The LMRB is a well-known rainstorm-flood basin. Floods in the LMRB are mainly caused by heavy rain. The LMRB is dominated by regional floods, and basin-wide floods rarely occur. From upstream to downstream, the flood peak and flood volume have shown increasing trends. Meanwhile, moving further downstream, the flood season ends later. In the upstream areas, floods are mainly concentrated in the period from July to October, with the highest probability of floods occurring in August. For the downstream areas, the flood season is from August to October. Climate change is one of the major factors affecting the LMRB’s droughts and floods . Global warming is an indisputable fact. Under global warming, extreme hydrological events show a tendency to increase. Climate models have suggested a future potential for increased flood frequency, magnitude, and inundation in the LMRB by 10–140%, 5–44% and 19–43%, respectively. Although the severity and duration of droughts are also increasing, the differences in drought indicators projected by different climate models are significant. Hydropower development was another major factor affecting droughts and floods in the LMRB . Large-scale hydropower development has drastically changed streamflow characteristics since 2009, causing increased dry season flow (+150%) and decreased wet season flow (−25%), as well as reduced flood magnitude (−2.3 to −29.7%) and frequency (−8.2 to −74.1%). Large-scale reservoirs will have a profound impact on hydrological characteristics, droughts and floods, agriculture, fisheries, energy supply, and environmental protection in the LMRB. Coupling climate models and hydrological models is the main way to study the impact of climate change and reservoir operation in the LMRB . Climate change indirectly affects hydrological characteristics by affecting meteorological parameters, while reservoirs can directly change the propagation from meteorological extreme events to hydrological extreme events by releasing/storing water in different situations. Hydrological models are the link connecting and quantifying the coupled effects of climate change and reservoirs. More studies are needed to develop a comprehensive understanding of the future impacts of climate change and reservoir operation on extreme events in the LMRB, as well as adaptation and mitigation measures.
... The delta's hydrologic regime is complicated, with two major distributaries -the Mekong (Tien River) and the Bassac (Hau River) -draining into the East Sea through eight estuaries (Anh et al., 2019), with the hydrological cycle influenced by the tropical monsoon climate (Costa-Cabral et al., 2008;Delgado et al., 2012). Approximately 75-85% of the total annual flow of the rivers in VMD is concentrated in the rainy season leading to flooding in the large area of the downstream delta (Hoang et al., 2016). The average discharge in the dry season fluctuates greatly, from 1700 m 3 /s to 6000 m 3 /s between January and May, leading to water shortages for irrigating about 1.5 million hectares of irrigated crops (Le et al., 2008). ...
... Climate risk assessments use downscaled climate from global climate models (GCMs) to drive models of freshwater flow and temperature. Results are then used to assess the risk of droughts and extreme temperatures that could constrain electricity generation (Hoang et al., 2016;van Vliet et al., 2012). Thermal risk is typically estimated as the frequency of violating upper temperature thresholds. ...
Anthropogenic changes in water temperature can pose significant risk to thermoelectric and hydroelectric generation. In this study, we developed indicators of thermal risk (ITRs) to assess risk to water-dependent electricity generating assets under future climate. We projected future changes in water temperature and quantified ITRs for plants across the conterminous US for a baseline and future period. One goal of our study was to tailor ITRs to measure climate risks mediated by aquatic biota. When using local species’ thermal tolerances as thresholds, we estimated that future conditions would expose an additional 53 GW or 30 % of once-through-cooled thermoelectric power (OTE) capacity and an additional 7.1 GW (10 %) of total hydropower capacity to slightly higher risk. Meanwhile, the future proportion of species exposed to risk increased by 25 % (OTE) and 15 % (hydropower). Because seasonal timing can be important when understanding competing demands for cold water, we developed two metrics of risk timing (median date of exceeding thermal thresholds and the duration of exceedances). Although changes were small (<5 d) for most plants, for some plants timing shifted by +/- five weeks and for others the duration of exceedances increased by 10 to 15 d. Geographically, elevated future risk was highest for plants in the southeastern US, reflecting future exposure to warming and the high aquatic biodiversity of rivers draining to the Gulf of Mexico and South Atlantic coast. We discuss how results from our ITR analysis can be used to plan climate-adaptation measures at both grid and plant scales.
... RSLR will also likely bring additional pressures on the water-related safety and sustainability of this region, as pointed out by many authors [18,23,37,65]. The cumulative impact of subsidence and sea-level rise will increase risks of inundation both in space and frequency. ...
The Mekong Delta has the world’s third-largest surface area. It plays an indisputable role in the economy and livelihoods of Vietnam and Cambodia, with repercussions at regional and global scales. During recent decades, the Vietnamese part of the Mekong Delta underwent profound human interventions (construction of dykes and multi-channel networks), which modified the hydrodynamic regime, especially cycles of field submersion. In this study, we first applied a full 2D numerical hydraulic model, TELEMAC-2D, to examine the effects of the complex channel and river networks on the spatial and temporal distribution of the flow in the 40,000 km2 of the Vietnamese Mekong Delta. Then, two scenarios of relative sea-level rise in 2050 and 2100 were implemented to simulate the future patterns of water fluxes in the delta. The results show that dykes and multi-channel networks would reduce the inundation area by 36% and lessen the peak water level by 15% and the discharge over the floodplains by 24%. Despite this protection, under a relative sea-level rise of 30 cm and 100 cm, the maximum flooded area could occupy about 69% and 85% of the whole delta in 2050 and 2100, respectively.
... The severity of historical flooding has already been underscored in terms of its components, including flood extent, volume, and resultant damages; for instance, extreme flooding in 2000, 2001, and 2011 dictated massive damages in the LMB of over 1.2 billion US$ combined, not to mention casualties and damages between 2002(MRC, 2015. Prospectively, climate change effects will be attended by significant changes in hydrological extremes in the MRB (Hoang et al., 2016). Likewise, Try et al. (2020b) attested substantial increases in high flow in the MRB and peak flood extent along with other flood attributes in the LMB by the end of this century as a result of climate. ...
... Climate change is one of the main trigger to increase the magnitude and severity of extreme floods in the LMB (Hoang et al., 2016;Perera et al., 2017;Try et al., 2020aTry et al., , 2020bVästilä et al., 2010). This study used a super-high-resolution Atmospheric General Circulation Model (MRI-AGCM3.2S) with 20 km spatial resolution (Mizuta et al., 2012) and a large ensemble Database for Policy Decision-Making for Future Climate Change (d4PDF) with 60 km (Mizuta et al., 2017) as main input for climate change on flood hazard and agricultural damage investigation. ...
Study Region: Mekong River Basin Study focus: Climate change has become a global environmental and socio-economical issue potentially affecting river hydrology and downstream flood characteristics. Climate change and upstream dam construction are the two main driving factors in altering the hydrology in the Mekong River Basin. Cambodian floodplain is located in the vulnerable flood zone to be affected by climate change and upstream dam development. This study investigated the potential impacts of future climate change and dam construction on flood hazards and agricultural damages in the Cambodian floodplain of the Mekong River. Climate outputs from MRI-AGCM3.2S under different sea surface temperature (SST) scenarios and a large ensemble climate dataset (d4PDF) under 4 K increasing scenario were used as input to a fully distributed rainfall-runoff-inundation (RRI) model for future projection of flood in the Lower Mekong Basin. New hydrological insights for the region: The results indicated that the changes in extreme flood events (25-year flood) showed an increase of agricultural flood damages under climate change impact by 18-28% under different SST scenarios. These increases would be only 5-13% under integrated impacts from future climate change and dam construction. Under the 4 K increasing scenario, the agricultural damages for extreme flood events of 10-year, 50-year, and 100-year return periods would increase by 32%, 38%, and 39% for climate change impact alone and 17%, 29%, and 31% for combined climate change and dam development scenario, respectively. The climate change impacts would have more influential on increasing the magnitude of extreme floods than the reduction caused by dam reservoir constructions in the future projection in the Cambodian floodplain of the Mekong River Basin. The impact of dam constructions tends to have greater impact on reducing smaller extreme events; however, their impacts are relatively smaller for larger extreme flood events (i.e., 100-year flood).
... Extreme event analysis310 Extreme low flow events were classified as values below the lower 5 th percentile of the 311 reconstruction mean(Higgins et al., 2022;Hoang et al., 2016). Similarly, extreme high flows were 312 above the 95 th percentile. ...
... show that monthly runoff increases at representative stations, except for a decrease in May−June. The study (Hoang et al., 2016) also finds higher monthly runoff at all MRB stations, except for a slight reduction in June. In terms of time distribution ...
The Mekong River (MR) crosses the borders and connects six countries including China, Myanmar, Laos, Thailand, Cambodia, and Vietnam. It provides critical water resources and supports natural and agricultural ecosystems, socio-economic development, and livelihoods of the people living in this region. Understanding changes in runoff of this important international river under projected climate change is critical for water resource management and climate change adaptation planning. However, research on long-term runoff dynamics for the MR and the underlying drivers of runoff variability remains scarce. Here, we analyse historical runoff variations from 1971 to 2020 based on runoff gauge data collected from eight hydrological stations along the MR.With these runoff data, we then evaluate the runoff simulation performance of four global climate models (GCMs) and five global hydrological models (GHMs) under the ISI-MIP project. Furthermore, based on the best simulation combination, we quantify the impact of future climate change on river runoff changes in the MR. The result shows that the an nual runoff in the MR has not changed significantly in the past five decades, while the establishment of dams and reservoirs in the basin significantly affected the annual runoff distribution.WaterGap2 forced by GCMs ensemble-averaged climates has the best runoff simulation performance. Under representative concentration pathways (RCPs, i.e., RCP2.6, RCP6.0 and RCP8.5), runoff of the MR is projected to increase significantly (from 3.81 m3 s−1 a−1 to 16.36 m3 s−1 a−1). In particular, under the RCP6.0 scenario, the annual runoff increases most significantly in the middle and lower basin due to increased precipitation and snowmelt. Under the RCP8.5 scenario, the runoff distribution in different seasons varies significantly, increasing the risk of flooding in the wet season and drought in the dry season.
... Rasanen et al. (2012) using hydrological and reservoir modeling had shown that in the future when the terraced hydroelectric dams on the Chinese side are completed, it will increase the dry flow to Chiang Sean station (Laos) by about 34-155% and decrease by 29-36% in the first months of the flood season [1]. Several studies related to the impacts of changes of climate and cascade on water resources in Mekong river basin, specifically on the 2S rivers were examined by Hoang et al. (2010) and Lauri et al. (2012) [2] [3]. The 3S tributary (Sekong, Srepok and Sesan) was simulated streamflow under the impact of dam development and operation but did not consider the effects of climate change [4]. ...
Water resources are increasingly scarce and depleted owing to the effects of local socio-economic development. Hydropower development changes the hydrological regime and the amount of alluvium downstream through the process of reservoir regulation and operation. To evaluate the potential of reservoir effect on river basin flow, we performed a flow assessment in the presence of structures and compared it with control case in which there are no reservoirs. In the Srepok river basin with many hydroelectric power plants built on terraces on rivers. Due to the dense construction surrounding the river, the flow has changed and there have been incidents of hydropower causing damage to crops and households. The results show that, in general, due to the influence of hydroelectric reservoirs, the annual flow is not significantly reduced and the amount of alluvium tends to increase. This research was conducted to provide comprehensive information on hydropower development, and at the same time provide a reliable source of information to help managers make timely and accurate decisions.
... Other spill-over effects of high-dike developments are associated with changed local floodwater dynamics and decreased flood water retention capacity in the upper Mekong delta, which increases flood risks in surrounding and downstream areas (Le et al., 2007;Triet et al., 2017;Trung and Tuu, 2012). Furthermore, the irrigation networks and dike systems have enabled salt water to flow further inland in the dry season (Hoang et al., 2016;Tuan et al., 2007). Some studies emphasise the exclusion of land-poor farmers due to profit marginalisation and second-order impacts such as increased degrees of specialisation and larger workloads, leading to further out-migration of the more productive part of the workforce Tran, 2019). ...
Intensive agriculture is increasingly associated with environmental degradation that may jeopardise long-term environmental and economic sustainability. The high-dike system in the upper Mekong delta that has enabled intensive rice cultivation represents a prime example of these potential negative feedbacks. The lack of seasonal flooding and the associated depletion of nutrients is expected to affect farmer income as productivity declines and more fertiliser is required. Therefore, emphasis has shifted towards more sustainable, flood-based agriculture, however farmer uptake has its challenges. Based on a compilation of different household surveys we first analyse rice farmers’ ability and willingness to transition and subsequently study the economic sustainability of intensive rice-based livelihoods. A Motivation and Ability (MOTA) survey reveals that two-thirds of the surveyed rice farmers are reluctant to change to flood-based farming systems, as they consider rice cultivation to be economically viable in the near future. They also mention financial and technical ability as key constraints. Subsequently, we analyse yield and fertiliser developments for a large sample of farming households under different dike systems between 2008 and 2015. This shows that income from rice farming grew steadily under high-dike systems as productivity growth compensated for higher input requirements. This growth is partly dampened by the slightly higher negative impacts of potential flood damage in high-dike areas, compared low-dike areas. A counterintuitive effect that is related to the fact that high dikes remain prone to dike overtopping or breaching in the flooding season, resulting in potentially higher damage than low-dike areas that are able to crop flood-based alternatives. The observed growth in income is a likely explanation for the reluctance to change in the studied period. Our analysis also shows that rice income growth is unequally distributed in high-dike areas, with lower incomes being associated with new high-dike systems and slower growth of incomes of smallholder rice farmers compared to large-scale farms. This makes smallholder rice farmers in high-dike areas especially vulnerable to changing conditions, and thus a priority target group for policy makers promoting flood-based alternatives. Recent commune level yield data show that the past productivity growth has stalled, increasing the prospects for alternative flood-based agriculture. This transition can be facilitated, by enhancing the economic viability of flood-based crops and, particularly for smallholder farmers, by improving their financial and technical capabilities through supportive policies.
