The Response of Water Balance Components to Land Use and Land Cover Change Based on Hydrologic Modeling in Bogena Watershed, Upper Blue Nile Basin, Ethiopia

Abstract

This study investigates the effects of land cover change on the water balance components using an integrated hydrologic modeling approach. Hydrologic modeling and water resources management studies is strongly interrelated to the spatial processes of the hydrological cycle. These rotations are showy by various factors like land use / land cover and climate changes. Deforestations are day to day movement of the people presented in the Bogena watershed; the area is facing high erosion due to forceful rainfall that intensifies the land cover change of the watershed. This study aimed to assess the effects of land use/land cover (LULC) changes on the streamflow of the Bogena Watershed using Geographic Information System (GIS), the Soil and Water Assessment Tool (SWAT), and SWAT-CUP. Input data for SWAT are climate data, soil, Land use and land covers data, and DEM. The land cover maps were produced using the Maximum Likelihood Classifiers of Supervised Classification. The model was calibrated using stream flow data from 1991 to1997, validated from 1998 to 2003 and from 1989-1990 used for warm up period. The R² and NSE values were used to evaluate the model performance. The results indicated that the R² values were 0.997 and 0.988, while the NSE values were 0.86 and 0.79 during the calibration and validation periods, respectively.  The results showed that land use/land cover (LULC) changes had significant effects on runoff production, infiltration rates, water yield, sediment loading, evapotranspiration, and the soil's water preservation capacity. The analysis also indicated that streamflow during the wet season increased, whereas streamflow during the dry season decreased. Between 1990 and 2015, surface runoff increased from 33.13 mm to 245.90 mm, representing an increase of 642.2%, while groundwater contribution decreased from 160.61 mm to 29.92 mm, representing a decrease of 81.4%. These changes were primarily attributed to the expansion of agricultural land and the legal and illegal extraction of groundwater for small-scale irrigation and other purposes. Overall, the hydrological regime of the watershed changed substantially during the 1990–2015 period as a consequence of LULC changes.