Evaluating the Performance of the WRF model in reproducing the Rainfall Onset and Cessation over Eastern Africa

Knowledge of the onset, cessation and length of the rainy season is important for decision-making in various climate sensitive sectors over Eastern Africa. In the agricultural sector for example the forecast information on these characteristics can be used to decide on when and what to plant.  We customize the Weather Research and Forecasting (WRF) model over the region and evaluate the skill of producing the onset and cessation over the region. The WRF regional climate model is utilised in sub-seasonal to seasonal forecasting over the region.  We utilize the threshold on accumulated rainfall method for calculating the rainfall onset and cessation as is currently done operationally over the region by the IGAD Climate Prediction and Applications Centre.   The customization experiments focus on the land surface, cumulus and microphysics schemes for the long rains (March-April- May), June to September and the short rains (October-November-December). In this study 3 land surface schemes, 5 cumulus and 6 microphysics schemes are utilized in combination with other physics schemes.  The WRF model is able to simulate the seasonal rainfall over the region. In addition it is shown that some physics combinations represent the onset and cessation  dates  better compared to others. The preliminary results  highlight the usefulness of the WRF model in reproducing the onset and cessation characteristics over the region.