Using SWAT to model the response of evapotranspiration and runoff to varying land uses and climatic conditions in the Muringato basin, Kenya

Abstract

Evapotranspiration and runoff being the major outflows in a water balance help in accounting for the water losses from the land surface and the amount of water available to replenish the streamflow. Their trends over time are influenced by the changes in Land Use and Land Cover (LULC), and climatic patterns. Muringato basin located in the Upper Tana River Basin, Kenya has faced degradation over the years as a result of anthropogenic factors, with an increase in population and changing climatic patterns being noted. This necessitates monitoring, managing, and conserving the basin for its sustainable utilisation. This research utilised remotely sensed data for the Muringato basin: Landsat satellite imageries, a digital elevation model, climatic data, and soil data to simulate the evapotranspiration and runoff from 1990 to 2020 while considering the changing LULC and climatic conditions in the Soil and Water Assessment Tool (SWAT) model. The model was satisfactorily calibrated and validated using the observed discharge data. The simulation results indicated that both outflow components account for 78% of the rainfall received in the basin. A 21.4% reduction in the forest cover by 2020 contributed to reduced evapotranspiration by 100 mm and increased runoff amounts by 5 mm. Therefore, the changes in the LULC and climatic patterns could easily alter the water balance. Thus, there is a need to formulate policies and sensitise the community on the importance of environmental conservation and its management. This would ensure that a healthy water balance in the Muringato basin is maintained.