Estimation of groundwater recharge using a GIS-based distributed water balance model in Dire Dawa, Ethiopia

Sustainable groundwater management requires knowledge of recharge. Recharge is also an important parameter in groundwater flow and transport models. Spatial variation in recharge due to distributed land-use, soil texture, topography, groundwater level, and hydro-meteorological conditions should be accounted for in recharge estimation. However, conventional point-estimates of recharge are not easily extrapolated or regionalized. In this study, a spatially distributed water balance model WetSpass was used to simulate long-term average recharge using land-use, soil texture, topography, and hydrometeorological parameters in Dire Dawa, a semi arid region of Ethiopia. WetSpass is a physically based methodology for estimation of the long-term average spatial distribution of surface runoff, actual evapotranspiration, and groundwater recharge. The long-term temporal and spatial average annual rainfall of 626 mm was distributed as: surface runoff of 126 mm (20%), evapotranspiration of 468 mm (75%), and recharge of 28 mm (5%). This recharge corresponds to 817l/s for the 920.12 km2 study area, which is less than the often-assumed 1,000l/s recharge for the Dire Dawa groundwater catchment.