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Assessment of Climate Change Impact on the Net basin Supply of Lake Tana Water Balance

Gebremariame, Zeryehun Haile (2009) Assessment of Climate Change Impact on the Net basin Supply of Lake Tana Water Balance.

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Abstract:Tana is the largest fresh water lake in Ethiopia and the main source of the Blue Nile. Climate change has a significant impact on lake hydrology more than human impact such as deforestation and diversion of lake water for irrigation. Therefore studying the impact of climate change on the net basin supply of Lake Tana is important for sustainable utilization of the water resource in Ethiopia. In this study the net basin supply of Lake Tana is predicted for different scenarios of climate change for three time windows: 2010-2039, 2040-2069 and 2070-2099. Net basin supply is the sum of all inflow to the lake and lake precipitation minus lake evaporation. Among the different GCMs the HadCM3 model is selected for this study since the model is widely used for climate change impact assessment. But the model output has coarse spatial resolution for this reason the statistical downscaling model (SDSM) is applied to downscale the climate variables to a finer resolution to match with hydrological modelling. For the SDSM the 30 years historic data of maximum and minimum daily temperature and rainfall of the three stations (Bahir Dar, Gonder and Debre Markos) were used. The downscaled data are used in hydrological model to forecast the inflow to the lake. Lake evaporation and lake precipitation are estimated based on the downscaled climate data of Bahir Dar and Gonder stations as well. The result of downscaling in the baseline period shows maximum temperature and the minimum temperature have better agreement with the observed results than the precipitation. The simulation of precipitation though showed a relatively lesser agreement as compared to the maximum and minimum temperature due to the fact that precipitation is the conditional process. Conditional process like precipitation is dependant on other intermediate processes like on the occurrence of humidity, cloud cover, and wet day occurrence. Unconditional process like temperature; however, are not regulated by other intermediate process. In addition local temperature are largely determined by regional forcing whereas precipitation series display more “noise” arising from local factor. Hence larger differences can be observed in precipitation ensemble members than that of temperature. The result of downscaling in the future scenario period indicates that the maximum temperature, minimum temperature and precipitation are increasing in the future times. As a result the mean annual lake precipitation, lake evaporation and inflow to the lake in the future period are higher than in the baseline period. But the increase in lake evaporation is obscured by the increase in lake precipitation and inflow, therefore the mean annual net basin supply shows an increasing trend in the future time. Key words: climate change; downscaling; Lake Tana; net basin supply
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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