Assessment of runoff and soil erosion patterns in the Namatala watershed using SWAT+

Abstract

Soil erosion and surface runoff are big problems for farming and water in many highland areas of Uganda, like the Namatala Watershed on the southeastern side of Mount Elgon. This area has become worse with time because more land is being encroached for farming, forests are being cut down, and people aren't managing the land well. In this study, we see how runoff and soil erosion change over time and space in the Namatala Watershed. We used a tool called SWAT+ along with GIS and satellite data. We fed the model data from a 30 m Digital Elevation Model, Sentinel-2 for land use and cover, SoilGrids for soil types, and NASA POWER for climate information. The watershed was divided into smaller areas called HRUs based on their land use, soil, and slope. We then checked how well the model matched real streamflow data and used metrics like NSE, PBIAS, and R² to see how good it was. The model worked well for both calibration and validation. We found that farms made up over half of the watershed's area, with grasslands covering about 37%. The way rainfall was split between different uses, like evaporation and/or becoming runoff, was heavily affected by the land use, soil, and how steep the land was. This study shows that SWAT+ can be useful for understanding runoff and erosion in places where data is scarce. The information collected can help decide where to direct conservation efforts to reduce erosion, improve land productivity, and make the Namatala Watershed more sustainable.