Risk assessment of flash flood situation under land use change using daily SWAT streamflow simulation in Loei Basin, Northeastern, Thailand

Abstract Flash flood typically occurs in the wet season caused by heavy rain from upstream to downstream and land use changes. This research mainly aims to apply SWAT model to assess the variation of streamflow in Loei Basin, Northeastern Thailand by comparing the daily streamflow during flash flood in the rainy season in the years 2002, 2011, and 2017. This included considering the three different time periods of land use change patterns input to SWAT to assess the impact on streamflow. The result revealed that daily SWAT streamflow simulation compared to data obtained from KH58A station in 2011 was reliable as could be seen from acceptable R 2 and PBIAS. In terms of the tendency of land use change, conventional agricultural was replaced with rubber plantation, sugarcane, and urbanization. From this situation, most flood risk areas occur along the mainstream from middle to northern of basin outlet, including being a municipal community area with a high density of residents. It is expected to be a risky area affected by the flood situation. The result of this research can be used as a guideline for land use and water resource management when encountering sudden changes in hydrologic conditions in the wet season.