HESSD Hydrology and Earth System Sciences Discussions HESSD Hydrol. Earth Syst. Sci. Discuss. 1812-2116 Göttingen, Germany 10.5194/hess-2021-527 Spatial and temporal simulation of groundwater recharge and cross-validation with point measurements in volcanic aquifers with variable topography Yenehun Alemu https://orcid.org/0000-0002-6580-8161 1 2 Dessie Mekete 3 Nigate Fenta 1 Belay Ashebir Sewale 1 2 Azeze Mulugeta 3 Van Camp Marc 2 Fenetie Taye Derbew 6 Kidane Desale 5 6 Adgo Enyew 6 Nyssen Jan https://orcid.org/0000-0002-2666-3860 7 van Griensven Ann 4 Walraevens Kristine 2 School of Earth Sciences, Bahir Dar University, Bahir Dar, Ethiopia Laboratory for Applied Geology and Hydrogeology, Department of Geology, Ghent University, Gent, Belgium Faculty of Civil and Water Resources Engineering, Bahir Dar University, Bahir Dar, Ethiopia Department of Hydrology and Hydraulic Engineering, Vrije Universiteit Brussel, Brussel, Belgium Department of Soil Physics, Ghent University, Belgium Department of Natural Resources, Bahir Dar University, Ethiopia Department of Geography, Ghent University, Belgium 01 12 2021 2021 1 37 Copyright: © 2021 Alemu Yenehun et al. 2021 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://hess.copernicus.org/preprints/hess-2021-527/ The full text article is available as a PDF file from https://hess.copernicus.org/preprints/hess-2021-527/hess-2021-527.pdf

<p>A physically distributed water balance model called WetSpass is applied to estimate the recharge for the semi-humid Lake Tana basin in northwest Ethiopia. Lake Tana basin is one of the growth corridors of the country, where huge waterworks infrastructure is developing. Estimating groundwater recharge at required spatial and temporal scales is a challenge in groundwater management, sustainability and pollution studies. In this study, the WetSpass model is developed at 90 m grid resolution. The spatial recharge map by WetSpass is cross-validated with water table fluctuation (WTF) and chloride mass balance (CMB) methods. The mean annual recharge, surface runoff, and evapotranspiration over the whole basin using WetSpass are estimated at 315 mm, 416 mm, and 770 mm of rainfall, respectively. The mean annual recharge ranges from 0 mm to 1085 mm (0 % to 57 % of the rainfall): 0 mm at water bodies and highest on flat, sandy loam soil and bush land cover. Similarly, a high range of recharge is also noted using WTF and CMB methods showing the strong heterogeneous nature of the hydro(meteoro)logical characteristics of the area. Generally, the recharge is found higher in southern and eastern catchments and lower in the northern catchments, primarily due to higher rainfall amounts in the former parts. A fair general correlation between the recharge by WTF and WetSpass is found. WetSpass is effective in aquifers where diffuse recharging mechanism is the predominant type and recharge is controlled by rainfall. It is less effective in the storage-controlled flat floodplain alluvial and fractured rock aquifer areas. In these areas, the point estimates by WTF and CMB are effective and can be considered as reliable values. The land use change from 1986 to 2014 brought a relatively small hydrological change in recharge although the land use has changed significantly.</p>