Analysing the Impacts of Natural-Factor Variability on Lake Water Volume Using the Generalized Method of Moment

Abstract. Natural-factor variability strongly influences the hydrological stability of large tropical lakes. As a major freshwater resource in East Africa, Lake Victoria has experienced notable water-volume fluctuations under changing climatic conditions. This study investigated the effects of precipitation, evapotranspiration (ET), El Niño–Southern Oscillation (ENSO), and normalized difference vegetation index (NDVI) on lake water volume using multi-source datasets and the generalized method of moments (GMM). The results show that precipitation is the dominant positive driver of water-volume variation, whereas ET has a negative effect through increased surface-water loss. Quantitatively, the GMM estimates indicate that precipitation has a positive coefficient of 1.291, while ET shows a negative coefficient of −0.137. In addition, NDVI exhibits clear seasonality and reaches a monthly maximum of 0.7293 in December 2015, reflecting the close linkage between hydrological fluctuations and vegetation conditions in the basin. Overall, this study clarifies the main hydroclimatic controls on Lake Victoria water-volume variability and provides empirical support for regional water-resource assessment and climate-adaptation planning.