The dilemma of choosing appropriate groundwater recharge estimation methods in Ethiopia: A systematic review of the existing methods

Knowledge of groundwater recharge is a prerequisite for sustainable management of water resources. However, in Ethiopia, recharge estimation methodology remains haphazard regarding selection and application of various methods. Therefore, the objective of this study is to review commonly applied groundwater recharge estimation methods in Ethiopia, identify and analyze the main challenges and limitations that affect the reliability of recharge estimates, and suggest insights for future research. For this purpose, a systematic literature review is conducted focusing on Ethiopia and similar regions. About 87.8% of the reviewed studies have applied only one recharge estimation method. The selection of recharge estimation methods is mainly dependent on the availability of data regardless of their appropriateness to the actual field conditions and the inherent limitations of the methods. Comparatively, the WetSpass, SWAT, water table fluctuation (WTF), and chloride mass balance (CMB) techniques are frequently applied methods in a decreasing order of 20, 18, 13, and 12% respectively. Insufficient areal coverage of rainfall data, inaccurate estimates of evapotranspiration, low performance to simulate peak stream flow data, inadequacy of soil and rainfall chloride data, and misappropriation of recharge estimation methods to the actual field conditions are the main challenges for the rise of uncertainty of these methods. In general, recharge studies that have applied various recharge estimation techniques in Ethiopia have one limitation in common – i.e., failure to provide sufficient verification of results. Hence, this study shows that recharge estimations in Ethiopia are less reliable so that recharge values cannot be trusted to make robust water resources development plans. Therefore, selection of recharge estimation methods should rely on prior identification of recharge mechanisms and appropriation of the method to actual field conditions. The verification process should be accompanied by adequate field data measurements.