THE IMPACTS OF LAND USE LAND COVER CHANGE OF SELECTED HYDROLOGICAL PROCESS OF UNGAUGED KULUMSA SUB WATERSHED, RIFT VALLEY RIVER BASIN, ETHIOPIA

Abstract

Studying the response of watershed hydrology to land use and land cover (LULC) changes is attentional for water resources management and planning, Hence this study aimed to analyse the impacts of LULCC in the kulumsa subwatershed for the study period of 1986–2015 the supervised land use classification methods were used for classifying Landsat images (1995, 2005, and 2015). Soil and Water Assessment Tool (SWAT) for hydrological modeling was employed in the analyses. To divorce the impressions of LULC changes, the LULC maps were used independently while keeping the other SWAT inputs constant. The physical similarity index of the regionalization method was used to determine the Euclidean distance between the donor watershed and the site of interest to determine the similarity (s) of watersheds. The Similarity of the watersheds was 80% then the streamflow was converted by using the drainage area ratio method used for calibration and validation. The performance of the SWAT model was evaluated through sensitivity analysis, calibration, and validation. Ten flow parameters were identified to be sensitive for the streamflow of the study area and used for model calibration. The calibration and validation results showed that there was a good match between measured and simulated streamflow data with the coefficient of determination (𝑅2) of 0.78 and Nash-Sutcliffe efficiency (ENS) of 0.72 for the calibration, and 𝑅2of 0.80 and ENS of 0.77 of the validation periods. Results of LULC image classification and change detection in the study area showed there was a continuous expansion of agricultural land and built-up area, and withdrawing of forest and shrubs land during the 1986–2015 period. This results in Streamflow variation in the study area. Generally, the hydrological investigation concerning the land use and land cover change within kulumsa subwatershed showed that flow characteristics have changed, with an increase in surface flow and reduction of base flows through the selected period of study though for further investigation of the change it is also better to model the sediment yield in the area and dealing with climate change impact on selected hydrological process