A Comprehensive Analysis of Water Budget Components and Water Yield in the Upper Awash Sub-Basin, Central Ethiopia Using the SWAT Model

This study employed the Soil and Water Assessment Tool (SWAT) model to analyze the water budget components and water yield of the Upper Awash River sub-basin in Central Ethiopia. Utilizing data from 1986 to 2013, the model was calibrated from 1988 to 2008 following a three-year warm-up period and subsequently validated over five years at two gauging stations. Sensitivity analyses were conducted using t-stat and p-values, while model uncertainty was assessed using the p-factor and r-factor indices. The model's performance was evaluated using Nash-Sutcliffe efficiency (NSE), coefficient of determination (R²), and Percent Bias (PBIAS). Calibration results yielded p-factors and r-factors of 0.801 and 0.9 for Hombele, and 0.808 and 0.98 for Melkakuntro. The calibration R², NSE, and PBIAS values were 0.82, 0.82, and-2.3, respectively, for Hombele, and 0.79, 0.78, and-13.1, respectively. Validation R², NSE, and PBIAS values were 0.71, 0.67, 11.2 for Hombele, and 0.7, 0.66, 1.9 for Melkakuntro. The average annual groundwater recharge rate ranged from 0 to 904.3 mm, averaging 181.1 mm/yr, which accounts for 19.1% of the mean annual rainfall. The simulated mean annual surface runoff and evapotranspiration were 93.4 mm and 682.5 mm, respectively, constituting 9.8% and 71.8% of the mean annual rainfall. The average annual water yield of the study area was 233.4 mm. These findings provide important insights into the hydrological dynamics of the Upper Awash River sub-basin, deepening our understanding of this water system. This information is essential for establishing sustainable water management practices and optimizing resource use for socioeconomic growth.