Abstract
Future climate scenarios predict in general an increase in the temporal variability of hydro-climatic conditions. Around the rising trend in average temperature and rainfall, interannual and seasonal variation will increase. This will result in more frequent and more intense extreme events such as droughts. Drought affects many aspects of environment and society, and any future increases in the demand for water will be most critical in periods of severe drought. The identification, monitoring and characterization of droughts are of great importance in water resources planning and management. The water resource of the Blue Nile River is of key regional importance to the eastern Nile basin countries (Ethiopia, Sudan and Egypt). The Blue Nile originates from Lake Tana in the Ethiopian Highlands and contributes about 60 - 69% of the main Nile discharge. In this study, spatial and temporal dimensions of meteorological drought in in Blue Nile basin were investigated from vulnerability concept. Analysis of historical droughts was undertaken by converting observed monthly precipitation time series, of 11 meteorological stations over a 48-years period, to the Standardized Precipitation Index (SPI). The standardized precipitation index (SPI) was computed at multiple-time steps and the Mann - Kendall test was applied on monthly SPI time series for trend detection. Results indicate that droughts randomly affect the region and several drought events contain mild, moderate severe, and extreme droughts were observed during the long rainy season (June to September) and the short rainy season flow (March to May) as well. Trend analysis showed that most of the detected trends are statistically insignificant. Severity and frequency analysis of the monthly SPI index for studied station indicated that, on average, more than 35% of the months in all stations experienced droughts and their intensity various from moderate to extreme and the intense droughts were during the 1980s.