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Berhane Fisseha. Model based assessment of potential impacts of climate change on the flow of the main headwaters of the Nile River: Equatorial Lakes Region and Blue Nile basins (Under the direction of Dr. Richard Anyah).

Spatially and temporally detailed assessment of the hydrologic processes of the main sources of the Nile River headwaters (Blue Nile basin and Equatorial Lakes Region) is vital for basin-wide scale management to cope with the pressing water problems due to burgeoning populations, a growing demand for electricity, irrigation for food production and possible climate change.

The main objectives of this study were to use a physically-based, semi-distributed hydrological modeling system (Soil and Water Assessment Tool-SWAT) to study the hydrological processes of the Blue Nile and Equatorial Lakes Region subbasins, and investigate the potential impacts of climate change in the Blue Nile basin based on regional surrogate climate change scenarios (SCCS).

The lack of weather data is the main hindrance for hydrologic research in the Nile River basin. The distribution of the available weather and discharge observation stations is quite uneven. Moreover, the quality of the data is not reliable, and there are often large amounts of missing data. Required weather data for SWAT model, including daily precipitation, daily maximum and minimum temperature, were stochastically generated from the Climatic Research Unit (CRU) gridded monthly weather dataset using Monthly to Daily Weather Converter (MODAWEC). As it is difficult to manually calibrate such a complex model with many parameters, the Sequential Uncertainty Fitting (SUFI2) algorithm was used for calibration and to quantify uncertainty.

The model over the Blue Nile calibrates reasonably well bracketing 90% of the observed river discharge and introducing an R2 of 0.93 and Nash-Sutcliffe (NS) of 0.93 for calibration and R2 of 0.92 and NS of 0.92 for validation. The Equatorial Lakes Region has many lakes and data about the regulated lake Victoria were not found. This resulted in poor model performance. The study showed that downscaled gridded monthly weather data can be used in data scarce areas like the Nile basin where the measuring gages are small in number (not with the recommended density of observation stations), unevenly distributed and sometimes with much missing and erroneous data. The final goal of this study is to achieve an accurate representation of the monthly water balance with SWAT. It is unrealistic to model daily water flows using generated daily weather data. The study showed that SWAT can be used to study environmental change impacts on water resources and the competition for water resources by different sectors in the Blue Nile basin.

Surrogate climate change scenarios (SCCS) were used as input to the calibrated SWAT model to investigate the possible impacts of potential climate change on the hydrology of the Blue Nile basin. The surrogates were approximated using Intergovernmental Panel on Climate Change (IPCC-2007) data. Surrogates for A2, B1 and A1B were considered. The period from 1960-2000 was used as baseline and has been used to determine the changes and the effect of the surrogate climate changes. A simulation study of climate change effects on the basin demonstrates that the hydrology of the basin is very sensitive to climate change with 104%, 33% and 77% of the baseline increase to the surface runoff, lateral flow and water yield, respectively, for the A2 scenario surrogate.

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