Examining the impact of over-lake rainfall on Lake Victoria water level fluctuations
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Lake water levels fluctuate due to both natural human-induced factors. Variability in climate alters precipitation, driving fluctuations in lake water levels. Extreme fluctuations are usually responsible for flooding, water shortages, and alter lake water quality and ecosystems, as well as affecting fisheries and tourism. Lake Victoria, the world’s second largest fresh water source has been found to be fluctuating with rainfall and damming at the lake’s outlet being identified as the most affecting natural and anthropogenic factors respectively, which affects the approximately 340 million people that depend on it. This study therefore employed updated state of art satellite altimetry products from Topex/Poseidon, Jason1, 2, 3 and Sentinel 6A as well as CHIRPS rainfall data to give a 23-year understanding of how over-lake rainfall impacts water level fluctuations of Lake Victoria at annual and seasonal time scales from 2000 to 2022. Corrected satellite altimetry data shows that water levels were highest and lowest in 2019 (1139.5m) and 2006 (1137.1m) respectively accounting for 1.3m rise and 1.1m decline above and below the mean value of 1138.2m, above the reference Topex ellipsoid. Results from linear regression produced a P-value of 0.042 implying that statistically there was a significant relationship between water level fluctuations and rainfall over the lake at annual scale. Results were also statistically significant for the SON, JJA and DJF seasons while MAM produced insignificant results with P-values, 0.0016, 0.00000338, 0.000074367 and 0.1820 respectively. Overall, rainfall over the lake explained 17.94% of the water level fluctuations implying that further research should be conducted on other anthropogenic or natural factors (evaporation, in-flow and outflow) to see how they account for the fluctuation of the Lake.