Water Resources Studies in Headwaters of the Blue Nile Basin: A Review with Emphasis on Lake Water Balance and Hydrogeological Characterization

The Lake Tana Basin, comprising the largest natural lake in Ethiopia, is source and uppermost part of Upper Blue Nile Basin. In this review paper, research papers, mainly on rainfall-runoff modeling water balance, hydrogeology, have been reviewed. earlier balance estimation attempts used simple conceptual statistical approaches calculate a monthly timescale. More recent has using advanced semi-physically or physically based distributed hydrological models. Accordingly, mean annual precipitation over was estimated range 36.1–53.1%; evaporation at 45.3–57.5%; river inflow (all gauged ungauged) 43.6–63.9%; (lake) outflow 0–9.2%. With few isotope studies, groundwater are found insignificant. Different studies had recharge, ranging from 57 mm to 850 mm. basin heterogenous aquifer system consisting different volcanic rocks alluvio-lacustrine sediments. Generally, with low TDS, Ca–Mg–HCO3 type, isotopically relatively enriched, high Na–HCO3 depleted, types identified. major gaps such as hydraulic characterization, surface-groundwater interaction, flow Hence, future shall focus resources, so that existing surface updated usage options explored.