Assessing impacts of land use/land cover changes on the hydrology of Upper Gilgel Abbay watershed using the SWAT model

Abstract

The goal of this study was to examine how land use/land cover (LULC) changes affected the hydrology of the Upper Gilgel Abay watershed which is located in the Upper Blue Nile Basin. Landsat pictures (Landsat 5 TM 1986, Landsat ETM + 2003, and Landsat 8 OLI-TIRS 2021) were categorized into LULC classes using a technique of supervised classification, and the Soil and Water Assessment Tool (SWAT) was used to estimate the hydrological implications of LULC changes. During the 1986–2003, the result showed an increase in cultivated land (11.7%) and a decrease in forest (39.6%), shrubland (17.5%), grassland (5.6%), and water bodies. While cultivated land, grassland, and water bodies were decreased woodland and shrubland were grew up between 2003 and 2021. While surface runoff (6%) and water yield (1.8%) were increased groundwater flow (37.9), lateral flow (4.1), soil water (1.85), and evapotranspiration (2.2%) were decreased at a watershed-scale as result of the LULC changes between 1986 and 2003. In contrast, between 2003 and 2021, the average watershed surface runoff and water yield decreased, while lateral flow, groundwater flow, soil water, and evapotranspiration increased, owing to the growth of forest and shrubland and the decline of cultivated land. However, at the sub-watershed scale the impacts of spatio-temporal LULC variations on the investigated hydrological parameters throughout the 1986–2003 and 2003–2021 periods were not in the same direction. The findings point to increase plant cover in the study watershed, as well as the Ethiopian Highlands, as a way to reduce surface runoff and boost groundwater flow and soil water.