The Ethiopian highlands and its vicinity are the wettest areas in North-east Africa. This area (Lake Tana) is the source of the Blue Nile which contributes more than 80% of the total Nile water. It is clear from the time series plot that multi-decadal rainfall fluctuations occurred during the 20th century, with rainfall deficits dominating towards to close of the century. There is evidence of a likely continuation of the downward trend during the 21st century, especially after the third decade.
Though overestimating the rainfall amounts early in the rainy season, most models simulate the 20th century annual cycle acceptably well. There is evidence of a likely reduction in precipitation amounts at the start of the season, with most models predicting less rainfall in April in the future climate. This could be an indication of a likely shift in the onset of the seasonal rains. The models which showed a downward trend predict less rainfall amounts during the peak summer months though there is less consensus between the models in predicting the peak-season pattern of change.