Hydroclimatic variability over the Greater Horn of Africa during the transition between the bimodal rainfall regimes

We perform diagnostic analysis (NCEP and ERA) as well as regional climate simulation using RegCM3 model to investigate hydroclimatic variability during the transition between the two rainfall seasons MAM (long rains) and OND (short rains) of the Greater Horn of Africa (GHA). The GHA sub-region is prone to extreme climate events such as droughts and floods that have negative impacts on the key socio-economic sectors of all the countries in the sub-region. Most of these have been linked to the evolution of El Niņo and La Niņo events. Our study therefore specifically examines the characteristics circulation pattern and moisture transport anomalies observed during the various episodes of El Niņo and La Niņo years.

In this study we focus on five years, 1961, 1982, 1988, 1997 and 2005 that were not only characterized by different background climate regimes, but also different expression of extreme climate conditions over most parts of GHA sub-region. Whereas the peaks of El Niņo and La Niņo conditions coincide with peak of the OND (short rains) season, we are particularly interested in examining the climatic conditions during the transition (non-rainy) periods which have grater implications on key sectors such as water, agriculture and food security.

Our preliminary result based on analysis of velocity potential and moisture flux convergence fields shows that there is a distinct shift in the regions of moisture flux convergence and source regions during DJF and JJA of the La Niņo and El Niņo years. We consider this result to be of significance since it presents the possibility and potential to isolate ENSO signal in the region even as early as the February and March of the actual year that El Niņo and La Niņo episodes occur.