UC Davis

Water balance and drought analysis are crucial practices to reduce the effects of hydro-meteorological risks on human society in an economically and environmentally sustainable manner. Water withdrawal and water supply are changing dramatically in Vietnam due to the escalating pressure from socioeconomic development, environmental requirements, and climate change impacts. The IPCC has identified Vietnam to be amongst the countries most affected by climate change, predicting an increase in the frequency and magnitude of natural disasters, especially droughts and floods. Water resources in Vietnam are highly dependent on external sources, with over 60 percent of the total average surface water discharge generated outside of the country. The reliance on external sources poses an alarming threat of water scarcity, requiring immediate actions to cope with droughts and increase the resilience of Vietnam’s water resources. Thus, assessment of drought conditions over transboundary river regions is considered one of the most crucial tasks of the Government of Vietnam. The Lo River watershed (LRW), a tributary of the Red River watershed, is a transboundary watershed with a catchment area of 39,000 km2. The watershed is composed of upstream and downstream regions. The upstream region, located in China, accounts for 52% of the total area, while the downstream region, located in Vietnam, accounts for 48% of the total area. The main goal of this study is to assess drought conditions in the transboundary watershed LRW, based on long-term projected water supply and water demand under different 21st century climate change scenarios. The projected water supply is obtained by coupling a hydroclimate model whose inputs are provided by GCM projection outputs. Water demand, including municipal and industrial (M&I), environmental (E), and agricultural (AG), is collected from reliable sources. Future municipal and industrial (M&I) water demand and environmental water demand are collected from the Vietnamese Ministry of Natural Resources and Environment (MONRE), and the Ministry of Agriculture and Rural Development (MARD), respectively. Before projecting water supply, bias correction methods are investigated and applied. Bias correction combined with outputs from the hydroclimate model provide realistic flow data for the downstream region. Once projected water supply and water demand are obtained, a drought analysis is applied over the target watershed. Results of the drought analysis show future drought events are projected to be more intense and severe than past events. Increased understanding of the impact of climate change on future water resources aids policymakers in developing more effective plans to increase the resilience to climate change and sustain the water security of the region and the country.