El Nino Southern Oscillation link to the Blue Nile River Basin hydrology

The objective of this study is to evaluate the relationships of El Nino Southern Oscillation (ENSO) indices and the Blue Nile River Basin hydrology using a new approach that tracks cumulative ENSO indices. The results of this study call be applied for water resources management decision making to mitigate drought or flood impacts with a lead time of at least few months. ENSO tracking and forecasting is relatively easier than predicting hydrology. ENSO teleconnections to the Blue Nile River Basin hydrology were evaluated using spatial average basin rainfall and Blue Nile flows at Bahir Dar, Ethiopia. The ENSO indices were sea surface temperature (SST) anomalies in region Nino 3.4 and the Southern Oscillation Index (SOI). The analysis indicates that the Upper Blue Nile Basin rainfall and flows are teleconnected to the ENSO indices. Based on event correspondence and correlation analysis, high rainfall and high flows are likely to occur during La Nina years and dry years are likely to occur during El Nino years at a confidence level of 90%. Extreme dry and wet years are very likely to correspond with ENSO events as given above. The great Ethiopian famine of 1888-1892 corresponds to one of the strongest El Nino years, 1888. The recent drought years in Ethiopia correspond to strong El Nino years and wet years correspond to La Nina years. In this paper, a new approach is proposed on how to classify the strength of ENSO events by tracking consecutive monthly events through a year. A cumulative SST index value of >= 5 and cumulative SOI value of <=-7 indicate strong El Nino. A Cumulative SST index value of <=-5 and cumulative SOI index of >= 7 indicate strong La Nina. Copyright (C) 2009 John Wiley & Sons. Ltd.