| Summary: | A large amount of Nile water originates in Ethiopia. However, large uncertainty arises concerning whether land degradation or climate change is the cause for the observed increase in discharge along downstream countries. Previous studies showed increases in discharge at Kessie, Bahir Dar and El Diem over the past four decades with no increase in basin-average rainfall. They cite changes in landscapes or soil coverage as a potential reason for this change. However, the study in this thesis shows that the change in discharge could also be explained in part by spatial changes in precipitation. This thesis investigates trends in rainfall within the Blue Nile River Basin f rom 1963 to 2003. For this study total monthly and daily precipitation data were collected from across the Blue Nile River Basin and analyzed statistically. The results indicate spatial variability in the rainfall observed. The general long-term trends in annual as well as in seasonal precipitation show a general decreasing trend along southwest regions of the study area. However, an increasing trend was encountered along northeast and southeast region of the Basin (3 of 9 selected stations). Rainfall-runoff modelling was performed to estimate the required precipitation increase to produce the increase in discharge observed in the Blue Nile River Basin. Precipitation needed to increase between 10 % and 25 % to account for the increased discharge. This increase is similar to that observed for some of the precipitation stations showing that increase in discharge seen in the Blue Nile River Basin may in part be due to changes in precipitation.
|
|---|
