Simulation of runoff under climate change in the tropical Ba River basin, Vietnam

Tropical river basins exhibit complex hydrological dynamics and are increasingly susceptible to the impacts of climate change.However, there remains a lack of data and methodological frameworks to comprehensively assess runoff responses in these regions.This study proposes a framework for evaluating the impact of climate change on runoff in the Ba River basin.Long-term trends in temperature, rainfall, and discharge from 1981 to 2020 were analyzed.The SWAT model was applied to simulate future discharge under four climate change scenarios (SSP1-2.6,SSP2-4.5,SSP3-7.0, and SSP5-8.5)for the periods 2021-2040, 2041-2060, 2061-2080, and 2081-2100.Results indicate that annual discharge at the An Khe station (upper basin) is projected to decline by 30.2 to 39.0%, while the Cung Son station (lower basin) is expected to experience change ranging from -4.0% to +15.6%.During the flood season, discharge is projected to decrease at the An Khe station (-6.1 to -17.3%) but increase substantially at the Cung Son station (+32.0 to +57.9%).In contrast, low-flow season discharge is projected to decline sharply at both stations by 68.0 to 85.2% at the An Khe station and 86.7 to 98.6% at the Cung Son station.The anticipated reduction in lowflow-season discharge highlights critical risks for water security in tropical basins.These findings underscore the urgent need for improved management strategies and operational frameworks to ensure sustainable water use under future climate conditions.