ASSESSING THE IMPACT OF LANDUSE/LANDCOVER CHANGE ON THE HYDROLOGICAL RESPONSE OF KOLA RIVER WATERSHED, SIDAMA REGION, ETHIOPIA

Abstract

Landuse/land cover change is one of the major factors that affect the hydrological response of watersheds. Hence studying the impacts of past and future landuse/land cover changes on the hydrology of Watershed is very important for proper watershed management. This study investigated the past and potential future land cover changes and their impact on the hydrological response of the Kola River Watershed by using the Soil Water Assessment Tool (SWAT).To detect and analyze the change that had taken place in the study area, satellite images were downloaded for 1988, 1998, 2008, and 2018 years and processed using ERDAS Imagine 2014. Then by using the supervised image classification technique, the satellite images were classified to agriculture, agroforestry, built up pasture, land, and forest landuse the land cover types. Then accuracy assessment was done, and overall accuracy of 87.83%, 88.41%, 89.15%, and 91.76%, was achieved for the classified images of 1988, 1998, 2008, and 2018 respectively. The changes of landuse/land cover of the study area from 1988 to2018 indicated that Pastureland, Forest, and Agroforestry decreased by 69.55%, 40.86%, and 15.77%, while Agriculture, and Built-up, increased by 24.67%, and 23.9%, respectively. The future LULC of 2048 was projected by IDRISI (CA-Markov method) and the result indicated a continuous increase of Agriculture and Built-up areas as the other landuse land cover such as forest, pastureland and Agroforestry decreased. Model sensitivity analysis was made to choose the most sensitive parameters. Then, R2 and ENS achieved 0.87, 0.77 during calibration and 0.85, 0.74 for validation respectively. The model performance evaluation indicated that SWAT can be used for modeling the impact of historical and projected LULCC on the hydrological response of the study Watershed. As the investigation of 1988 to2018 shows, due to LULCC, the seasonal flow increased by 25.71%, 23.73%, and 19.96%in the first and, second rainy seasons, and short rainy season, while it decreased by 22.21% in the dry season respectively. The annual surface runoff and water yield increased and by 22.21%, and 3%, whereas evapotranspiration and lateral flow, decreased by, 6.21%, and 14.61% respectively. The future LULCC prediction of 2048 showed thatseasonal flow increased by 29.03%, and 28.08%, 14.6% in the first and second rainy season, and short rainy season and decreased by 19.3 in dry seasons. Generally, the investigation of hydrological response to LULCC by taking other data constantly at different predefined study years indicates LULCC has significant impacts on the hydrological response of the study watershed. Therefore to overcome the impact of LULCC, local and national policymakers should be invited to prepare and apply scientific and appropriate watershed planning and management, strategies in the Kola River Watershed