Impacts of Climate Change and Land Use Change on Flood Flow in the Ca River Basin (Vietnam)

The Ca River Basin, one of the largest transboundary basins in Viet Nam, located in the North Central region, regularly faces large flood events causing great damage to people’s lives and livelihoods. Enhanced extreme rainfall events induced by global warming could increase flood hazards over the basin, yet the risks remain poorly quantified. This study fills some of the research gaps on future flood hazards by providing the first flood risk assessment for global warming levels ranging from 1.5°C to 4°C above preindustrial level, also taking into account the major reservoirs. Changes in flood flow and downstream flooding situation for a typical flood event are simulated with coupled hydrological and hydraulic models. Results show a large increase in flood flow, with a doubling of peak discharge at the upstream stations on the Ca and Hieu river. Consistently, flooding status in downstream areas also presents more severe conditions, with increased depth and extent of the flood. At 3°C of global warming, the total simulated flooded area increases by up to 43% and an additional 24 communes are exposed to flood depths between 1.5–2.5 m. Reservoir inflows to Ban Ve, Ban Mong, and Ho Ho increase by 40–130%, exceeding designated flood storage. We conclude that addressing these challenges will require not only technical innovation but also institutional coordination and long-term strategic planning.