Surface Water Demand Analysis on South Gojjam Sub Basin of Upper Blue Nile, Ethiopia

Abstract

Rapid population growth and agricultural expansion strain water resources in Ethiopia's South Gojjam sub-basin, necessitating analysis of current and future surface water demands to ensure equitable allocation and prevent conflicts. Government data, with rainfall validated by non-dimensional and double mass curve methods, indicated 1,276 million cubic meters (MMC) potential. WEAP model validation using Birr gauge streamflow (1994–2022) showed strong performance: SDR = 1, RSR = 0.141, NSE = 0.976, PBIAS = -14%. Baseline (2024) demands—rural (70.88 MCM), agriculture (43.91 MCM), livestock (28.64 MCM), urban (24 MCM)—were fully met, allocating 20.8% of mean annual flow (265.83 MCM) to environmental flows. Projections to 2050 under four scenarios revealed demands of 167.72 MCM (Reference), 194.7 MCM (High Population Growth; shortages: urban 8.31 MCM, rural 7.52 MCM), 176.89 MCM (Current Irrigation Potential; agriculture 1.87 MCM shortage), and 188.32 MCM (Future Irrigation Projection; agriculture 3.47 MCM shortage). These results emphasize urgent needs for integrated water management strategies.