Assessing climate change impacts on flow regimes and sediment load in thailand’s upper Ping river basin, using the soil and water assessment tool (SWAT)

Abstract

Climate change can significantly alter river basin hydrology, sediment transport, and hydrological extremes, particularly in monsoon-dominated mountainous basins. This study assessed the potential impacts of climate change on streamflow, sediment load, and hydrological extremes in Thailand’s Upper Ping River Basin (UPRB) using the Soil and Water Assessment Tool (SWAT). The model was calibrated and validated using observed streamflow data from five gauging stations and sediment load data from two upstream stations for 2000–2022. Station-based rainfall and inverse distance weighting (IDW)-interpolated rainfall were compared to evaluate rainfall input representation. The calibrated and validated model was then driven by NEX-GDDP-CMIP6 EC-Earth3 climate projections under SSP2-4.5, SSP3-7.0, and SSP5-8.5 to simulate near-future conditions during 2025–2044. The results show that IDW-interpolated rainfall improved overall streamflow simulation performance, emphasizing the importance of spatial rainfall representation in the UPRB. Future projections indicate stronger seasonal hydroclimatic contrast, with wet-season rainfall increasing by up to about 8% and dry-season rainfall decreasing by up to about 29%. These changes result in wet-season streamflow increases of up to about 25% and dry-season streamflow reductions of up to about 38%, particularly in upstream areas. Sediment load responses are more spatially variable, with wet-season sediment load increasing by up to about 17% at P.4A but slightly decreasing at P.1, while dry-season sediment load decreases by up to about 51% at both sediment stations. Flow duration curve analysis indicates that high-flow conditions generally intensify by up to about 26%, whereas low-flow responses vary spatially, with stronger reductions in sensitive upstream areas. Flood frequency analysis shows that flood magnitudes generally decrease across most stations and return periods by up to about 36%; however, rare high-magnitude floods may still increase locally at P.4A under SSP5-8.5 and Bhumibol Dam under SSP3-7.0. Overall, the findings suggest that climate change may intensify both hydrological regimes and sediment dynamics in the UPRB, highlighting the need for adaptive reservoir operation, dry-season water allocation, upstream monitoring, and site-specific flood-risk management.