Evapotranspiration Dynamics in the Ribb Watershed Upper Blue Nile, Ethiopia.

Assessment of the spatiotemporal distribution of evapotranspiration is crucial for efficient water resource management, especially in irrigation-dependent regions. This study evaluated actual evapotranspiration (AET) in the Ribb watershed, Ethiopia, via the surface energy balance algorithm for land (SEBAL) with remote sensing and climate data. The analysis focuses on the temporal (daily, monthly, and seasonal) and spatial variability of AET under different land uses. The daily AET values ranged from 0 to 10.99 mm/day, with mean values between 1.97 and 5.15 mm/day. The highest AET (5.15 mm/day) occurred during the middle growth stage of irrigated crops in January, whereas the lowest values (1.94 mm/day) were observed during the initial and end growth stages in December and February. The forest areas and water bodies presented high daily and seasonal AET values, whereas the agricultural fields and bare lands, which were mostly dry during the study period, presented lower ET values. Validation against ground-based pan-ET measurements and the Penman-Monteith (PM) method revealed strong correlations (R² values of 0.86 and 0.81, respectively). A comparison with MOD16-ET products revealed lower correlations, particularly for agricultural and forestland use (R² values of 0.33 and 0.4, respectively). This study demonstrates that integrating the SEBAL model with remote sensing data provides a reliable method for estimating the spatiotemporal distribution of AET in various watersheds. This information is vital for optimizing water use, irrigation planning, and sustainable water resource management.