Spatial groundwater recharge estimation in Raya basin, Northern Ethiopia: an approach using GIS based water balance model

Understanding the spatial variability of groundwater recharge in response to distributed Land-use, soil texture, topography, groundwater level, and hydrometeorological parameters is significant when considering the security of groundwater resource development. Thus, this study was aimed at estimating the spatial groundwater recharge of Raya valley, northern Ethiopia using spatially distributed water balance model (WetSpass). Input data for the model were prepared in the form of grid maps using 90 m grid size and the parameter attribute tables were adjusted to represent the Raya valley condition using expert knowledge and scientific literatures. The results of the model indicated that the long-term temporal and spatial average annual rainfall of 710 mm was partitioned as 57 mm (8%) of surface runoff, 598 mm (84%) of evapotranspiration, and 55 mm (8%) of recharge. The recharge corresponds to 137 million cubic meters (Mm3) for the Raya basin (with area of about 2500 km2) from which 84% of the recharge takes place during summer season, while the remaining 16% takes place during the winter (dry) season. The analysis of the simulated result showed that WetSpass works well to simulate water balance components of Raya valley and is especially suitable for studying the effects of Land-use changes on the water regime in the basin.