Water balance of Lake Tana and its sensitivity to fluctuations in rainfall,Blue Nile basin,Ethiopia |
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| Affiliation: | 1. Cornell University, Ithaca, NY, USA;2. Bahir Dar University, School of Civil and Water Resource Engineering, Bahir Dar, Ethiopia;3. International Water Management Institute (IWMI), Addis Ababa, Ethiopia;4. Pasture Systems and Watershed Management Research Unit, USDA-ARS, University Park, PA, USA;1. Blackland Research and Extension Center, Texas A&M Agrilife Research, 720 East Blackland Road, Temple, TX 76502, USA;2. Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY, USA;3. USDA-ARS, University Park, PA, USA;4. School of Civil and Water Resource Engineering, Bahir Dar University, Bahir Dar, Ethiopia;5. International Water Management Institute, Addis Ababa, Ethiopia |
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| Abstract: | The annual water budget of Lake Tana is determined from estimates of runoff, rainfall on the lake, measured outflow and empirically determined evaporation. Simulation of lake level variation (1960–1992) has been conducted through modeling at a monthly time step. Despite the ±20% rainfall variations in the Blue Nile basin in the last 50 years, the lake level remained regular. A preliminary analysis of the sensitivity of level and outflow of the lake suggests that they are controlled more by variation in rainfall than by basin-scale forcing induced by human activities. The analysis shows that a drastic (40–45%) and sustained (7–8 years) rainfall reduction is required to change the lake from out flowing to terminal (cessation of outflow). However, the outflow from the lake shows significant variation responding to the rainfall variations. Unlike the terminal lakes in the Ethiopian rift valley or the other large lakes of Tropical Africa, at its present hydrologic condition, the Lake Tana level is less sensitive to rainfall variation and changes in catchment characteristics. |
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