Spatial And Temporal Characteristics Of Thunderstorms Over The Eastern Region Of Lake Victoria Basin In Kenya
Weather is very important on human activities over western Kenya just like the rest of the world. It affects lives in different ways, including the food and water resources. Western Kenya is the food basket of the country. The inhabitants depend on agriculture for food and socioeconomic developments. Accurate information on thunderstorms (TS) could therefore assist in the planning and management of agricultural production, water resource management, aviation safety, communication and environmental protection among others. Thunderstorms being one of the most significant weather parameters are of great concern to forecasters. Thunderstorms may cause large damages to infrastructures and population, therefore, possible identification of the areas with the highest occurrence of these events is especially relevant. Studies have been done on organized convection in Africa and East Africa but not much over the Eastern part of the Lake Victoria basin in Kenya. This study investigates the spatial, temporal and propagation characteristics of thunderstorms to the east of the Lake Victoria basin in Kenya. The study focuses on March–May (MAM) and September-October (SON) seasons which recorded high thunderstorm occurrences. The data used consisted of observed thunderstorm data (2000-2013) from Kenya meteorological services for four synoptic stations to the east of Lake Victoria. Other datasets used were cloud top temperature (2006-2008) and the wind data (2006-2008) from the European center for medium range and weather forecasting. The data were subjected to several analyses which included frequency analysis, the longitude-time analysis (Hovmoller diagrams), and wind pattern analysis. The study showed that within the study period (MAM), the year 2006 recorded high thunderstorm occurrences while lower thunderstorm frequencies were reported in 2007 for both MAM and SON seasons. High thunderstorm frequencies were recorded during the SON season in the year 2008. The three years were chosen because the pattern of thunderstorm occurrence from the temporal graphs was more consistent (TS frequencies were increasing /decreasing in all stations). Temporal analysis of the observed thunderstorm data showed that thunderstorm frequency peaked between 1200 UTC and 1500 UTC when maximum convection is attained. The longitude-time vi analysis showed that organized convection evolved from the heat source, Mau Hills (~35.50E) and propagated westwards towards the lake. Some of the convective cells dissipated before reaching the lake. The wind analysis at low, medium and upper levels (850mb, 700mb and 200mb) respectively, revealed the circulations associated with thunderstorm characteristics over the study area. The levels 850mb and 700mb showed the areas with calm conditions and the moisture source, hence indicating if the region of study was under deep convection or not. The 200mb level revealed the direction in which the organized convection shifted. Results from this study provided information that can be used in water planning through water harvesting when severe storms occur in the area of study during the MAM and SON seasons. The information can also be used for disaster risk reduction by issuing early warning to residents living in lowland so that they can move to higher ground in case of floods as a result of severe storms. Dykes can also be built along the river banks well in advance to avoid overflowing waters from submerging the surrounding lands. The transportation industry, particularly Aviation, can also benefit from timely forecasts for aircrafts approaching the international airports in the region. The information on the evolution and propagation characteristics of thunderstorms can also be used by Kenya Meteorological Department (KMD) to come up with thunderstorm forecasts in support of sustainable livelihoods and development of the nation.