Spatio-temporal groundwater recharge estimation of Mount Guna, Northwest Ethiopia

Headwater of Upper Blue Nile, and Tekeze Basins, Northwest Ethiopia Spatially distributed water balance model WetSpass was chosen to estimate spatial and temporal recharge and evapotranspiration of Mt. Guna. Field based data and remote sensing data were used to successfully run WetSpass Model. The observed meteorological input data were corrected to minimize topographical effect by developing a regression equation, which is crucial in recharge estimation for such mountain site. The model was calibrated based on WetSpa model surface runoff result obtained from observed average discharge data collected at six river gauges. The recharge estimated by Water Table Fluctuation (WTF) and Chloride Mass Balance (CMB) methods was used to validate the model. The comparison of calibrated WetSpass estimated mean monthly runoff and the mean monthly WetSpa model results of surface runoff (2018–2020) shows a strong coefficient of determination (97 %) with the Nash-Sutcliffe Efficiency of 0.77. The mean annual recharge estimated by WetSpass is 409 mm in Mt. Guna. The recharge accounts for about 27 % of mean annual rainfall (1524 mm) received in Mt. Guna. On the other hand, the mean annual recharge of Mt. Guna estimated from Water Table Fluctuation and Chloride Mass Balance methods respectively is 357 mm and 417 mm. This confirms that WetSpass is effective to estimate spatial and temporal recharge in mountains. However, the meteorological inputs and water level data should be corrected to minimize topographic effect in similar mountains by following the methods we applied in this study. • A regression equation was developed for rainfall, temperature and evaporation to account for altitude. • WetSpass, Chloride Mass Balance and Water Table Fluctuation methods show a similar mean annual recharge with a slight variation. • Spatio-temporal variations of recharge observed in Mt. Guna is attributed to land cover type, geology, and rainfall characteristics.