Evaluating the impacts of climate and land use/land cover (LU/LC) dynamics on the Hydrological Responses of the Upper Blue Nile in the Central Highlands of Ethiopia

Abstract

This study integrates GIS and SWAT model to evaluate impacts of climate and LU/LC change on watershed hydrological dynamics. To evaluate the impact of a combined and individual climate and LU/LC dynamics on stream flow, series of simulation were computed by changing climate and LU/LC variables. The model was calibrated and validated against observed data. Statistical measures like coefficient of determination and Nash–Sutcliffe were used to evaluate the model and it results in 0.82 and 0.82 for calibration and 0.81 and 0.80 for validation respectively. During the study period, forest and shrub land decreased by 38% and 48% while, settlement and cultivated land increased by 572% and 7% respectively. Mann–Kendall trend test analysis showed a significant trend in maximum and minimum temperature at 5% significant level, whereas there were three no trend cases for rainfall out of four tested cases and one non-significant decreasing trend. The simulated flow showed a very good agreement with the observed flow data with 0.82 and 0.82 for calibration and 0.81 and 0.80 for validation respectively. Simulation result indicted that LU/LC change increased the wet season flow by 14.5% while decreasing by 9.65% in dry season. In wet season the flow increased by 4.5% while decreased by 3.3% in dry season because of change in climate and seasonal variability. The study showed the increase in stream flows can be directly attributed to the expansion of cultivated lands at a cost of the forested vegetation.