Modification and application of SWAT model to simulate a submerged rice paddy field

Given the extensive rice paddy fields in South Korea, accurate simulation of hydrological behavior in these fields is critical due to their considerable water resource usage. The soil and water assessment tool (SWAT) is commonly used to simulate watershed water flows and quality, including those in rice paddy fields. However, it lacks comprehensive consideration of submerging water conditions typical to South Korean rice paddies. Therefore, this study introduced a modification to the SWAT model to better simulate these conditions and assessed its feasibility in two distinct watersheds. The first application evaluated the impact of submerging water conditions on surface, subsurface, and base flows. The second assessed the impact of combined submerging water and fertilization conditions on the flow and water quality within the watershed. The findings indicated that submerging water conditions significantly affected runoff, and that water quality was responsive to different fertilization scenarios.