Analyzing the temporal variability of rainfall and its influence on the water levels over the Lake Victoria basin
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Understanding rainfall distribution is crucial for sustainable water resource management and several economic activities. This study investigated the temporal trends of rainfall in the Lake Victoria basin focusing on Entebbe region for the period of 30 years. An attempt was made to analyze the annual and seasonal trends of rainfall, and its influence on the fluctuations in the water levels of Lake Victoria. The study design involved collection and analyses of both rainfall and water level data. Station based meteorological and hydrological data were processed to obtain areal averages for simulation. The methodology consisted of trend analysis of rainfall and water level data sets. Normalization of raw data for both annual rainfall and water level averages were considered so as to add more meaning to the results. Percentage change method was applied to determine at what rate water levels have been fluctuating. Coefficient of variation formula was also applied to the rainfall data on a monthly basis, seasonally and annually in order to determine the variation of rainfall. The study also involved correlation analysis method to establish whether there is a relationship between rainfall and water levels. Study results showed that there is consistent increase in water levels of Lake Victoria for the past 30 years. The rainfall trend line showed a non-significant trend as tested by Mann Kendall. Time series statistical tests were applied to examine the temporal trends in three-time segments (1991– 2000, 2001–2010 and 2011–2020) and results showed that rainfall increased intensely post 2010s. There was noticeable variation of seasonal rainfall with rainfall varying much more in dry seasons (JJA & DJF) than in rainy seasons (MAM & SON). Percentage change method estimated the rate of change of water levels under varying rainfall characteristics. Significant correlations were observed between rainfall and water levels although a weak relationship exists. The study concludes that rainfall influences the lake levels at a lesser extent although recommends considering analysis at other different points of the Lake Victoria basin. Rainfall analysis across the whole Lake Victoria basin could be useful to support adaptation planning of the lake. The information obtained from this study could be used as input for decision-makers to take appropriate adaptive measures in various water resources sectors. Keywords: Rainfall variability, water levels, Lake Victoria.