Essential Ingredients and Mechanisms for Extreme Rainfall in East Africa During the 2016 El Nino

In East Africa where rainfall plays a crucial role in sustaining livelihoods and economic development, change in precipitation frequency, intensity and pattern have a profound societal consequence. While the mechanisms how the El Nino could impact rainfall in East Africa is not fully understood, it has been long known that the equatorial East Pacific sea surface temperature(SST) have effects on precipitation. After a strong El Nino episode in 2015-2016, it has observed the extreme precipitation that occurred in most of East African countries had claimed the life many individual and property damages during the month of May, 2016. In this paper we have analyzed the skill of the regional Weather Research and Forecasting (WRF) model in simulating extreme precipitation in in East Africa. The European Center Medium-Range Weather Forecast (ERA-Interim reanalysis), WRF-ERA and Global Forecast System (GFS), WRF-GFS reanalysis data were used for initial and boundary condition to force the model. In addition to the two forcing data sets used, sensitivity of the model to change in topography were assessed by changing terrain height. The result from the above simulation were compared to Tropical Rainfall Measuring Mission (TRMM) data. The results show that, both simulations using WRF-ERA and WRF-GFS forgings have captured the general spatial pattern of precipitation and location where extreme precipitation occurred but some with difference in amount and area coverage of precipitation. The WRF-ERA simulation overestimates precipitation in both amount and area coverage as compared to WRF-GFS. Precipitation simulation with terrain height set to zero depicts that, most of the area in the region has exhibited no or very small amount of precipitation in the regions, which shows that the interaction of large scale and local weather systems with topography plays a vital role in amount and distribution of precipitation in East Africa.