Assessment of the Streamflow and Evapotranspiration at Wabiga Juba Basin Using a Water Evaluation and Planning (WEAP) Model

Rapid population growth, industrialization, and agricultural activities have impacted water resources in the arid and semi-arid areas of Somalia. The Lower Juba region in Somalia has been the most affected region. Therefore, an analysis of the hydrological patterns is essential. This paper assesses streamflow and evapotranspiration in the Wabiga Juba basin in Somalia using a hydrological simulation model, namely, the water evaluation and planning (WEAP) system via the soil moisture method. The datasets included 53 (average precipitation) and 13 (streamflow) year periods from two meteorological stations. The estimated values for potential evapotranspiration (11,921.98 to 20,775.39 MCM) were higher than the actual evapotranspiration (4904.10 to 8242.72 MCM) by 50 to 79.5%, respectively. The annual streamflow in Juba Dolow and runoff proportion of the Wabiga Juba River was estimated to be 10% of the annual precipitation. Most of the surface runoff occurred in April (47%), May (31%), October (5%), and November (14%). The streamflow variation responded to the pattern of precipitation. The model performance achieved a Nash-Sutcliffe model efficiency (NSE) coefficient of 0.71, coefficient of determination (R2) of 0.91, and percent bias (PBIAS) of 14%. The WEAP model of the Wabiga Juba basin is a baseline study for water resource management in Somalia to mitigate water shortage impacts due to limited water resources.