Integrated assessment of the landuse change and climate change impacts on the sediment yield in the Songkhram River Basin, Thailand

The Songkhram River Basin (SRB) is the second largest river basin in Northeast Thailand. The nourishment of the SRB community mainly depends on water resources, especially fisheries. However, changes in land use and climate are causing problems to the livelihood of the SRB community. For sustainable water resources management, an integrated impact assessment of climate and land use change on sediment yield is crucial. Therefore, this study quantifies the combined impact of climate and land use change on sediment yield using the Soil and Water Assessment Tool (SWAT). An ensemble of three Regional Circulation Models (RCM) from Coupled Model Intercomparison Projects (CMIP5s) was used for future climate projection under representative concentration pathways RCP 4.5 and RCP 8.5. The projected climate shows a rise in both minimum and maximum temperature over 4.7 °C and a fall in precipitation over 6% by the 2080s. For land use, two scenarios, namely; economic and conservation, were developed using the land use change model, Dyna-CLUE. The simulated outcomes illustrate that, in the future, climate change is projected to cause a decrease in flow by 42.8% and 51.7% under RCP 4.5 and RCP 8.5, respectively. On the other hand, the land use change is expected to increase the sediment yield in future. It is responsible for an increase of 2.3% and 7.1% under economic scenarios, a decrease of 0.9%, and an increase of 3.9% under the conservation scenario, respectively, under RCP 4.5 and RCP 8.5. Overall, climate and land use change play a contrasting role in the study area. The combined impact of both results in a decreasing trend of sediment yield by 40.5% and 44.6% under the economic scenario, and 45% and 47.8% for the conservation scenario under RCP 4.5 and RCP 8.5, respectively.