Examining observed and simulated extreme rainfall events over Lake Victoria Basin in Uganda

Abstract

Rainfall extremes have strong connotations to socio-economic activities and human well-being particularly in the Lake Victoria Basin (LVB) of Uganda. Timely and reliable prediction and dissemination of extreme rainfall events is therefore of paramount importance to the region’s development agenda. The main objective of this study was to contribute to the prediction of rainfall extremes over this region using a numerical modelling approach. Finalized reanalyzes from the National Center for Environmental Prediction (NCEP) were downscaled using the Weather Research and Forecasting (WRF) model and the output verified against rainfall observations from the Tropical Rainfall Measuring Mission (TRMM). To start with, this study investigated a 10-year TRMM rainfall record and revealed a 20-day period in which both extremely heavy and low rainfall was received. The rainfall during this period was then simulated using the WRF model with a particular interest of investigating the performance of different combinations of cumulus and microphysical parameterization along with the model grid resolution and domain size. The results showed that the model was able to simulate the rainfall events and the most satisfactory skill was obtained with a model setup using the Grell 3D cumulus scheme in combination with the SBU_YLin microphysical scheme. This study concludes that WRF can be used for simulating extreme rainfall over western LVB. In the other 2 regions, central and eastern LVB, its performance is limited by its inability to simulate nocturnal rainfall. Furthermore, increasing the model grid resolution showed good potential for improving the model simulation especially when a large domain is used.