Effect of Lake Surface Temperature on the Spatial Distribution and Intensity of the Precipitation over the Lake Victoria Basin

Abstract

series of sensitivity experiments are performed to investigate the response of precipitation over the Lake Victoria basin (LVB) to the changes of lake surface temperature (LST) using the Weather Research and Forecasting (WRF) Model. It is shown that the default LST initialized from NCEP FNL (Final) Operational Global Analysis is deficient for simulating the rainfall over the LVB. Comparative experiments demonstrate the unambiguous impact of LST on the intensity and pattern of the precipitation over LVB. Intensification/weakening of precipitation over the lake occur with increasing/decreasing LST for both uniform and asymmetrical LST distribution. However, the relationship between rainfall anomalies and LST variations is nonlinear. Replacing the LST directly derived from global weather forecast models by the mean area-averaged LST of Lake Victoria (approximately 24°C) leads to improved rainfall simulation. However, LST with realistic cross-basin gradient is necessary to obtain a rainfall pattern consistent with the observations. The fact that rainfall and wind patterns over the lake are sensitive to LST distribution suggests the need to monitor the mesoscale LST pattern for accurate weather and climate prediction over LVB. It is also found that although the LST distribution exerts significant impact on the observed rainfall pattern, the area and location of the rainband are quite persistent under different LST forcing. This suggests that although the details of the rainfall pattern over LVB are strongly influenced by LST, the broad rainfall pattern is likely controlled by the atmospheric circulation and orography in the region.