Multi-variate regression analysis of lake level variability: A case of semi-closed, shallow rift valley lake in Northern Tanzania

Abstract

Lakes are very important for domestic use, commercial purposes, and ecosystem sustenance; nevertheless, studies on how different stressors influence water resources are limited, posing challenges in the planning and managing of water resources. Lake Babati is one of the important lakes in the East African rift valley as a source of fish, drinking water, and hippopotamus habitat. The lake level has consistently declined, threatening the life of organisms depending on the lake. Nevertheless, no study postulated the reasons for its decline. Therefore, this study used statistical methods, regression analysis and HEC-HMS hydrological model to investigate the association and sensitivity of the hydrological components driving the lake level variability. Results showed that the Lake Babati level was significantly declining (p < 0.01) at a rate of 0.025 m yearly. The lake level variability was most sensitive to inflow, while outflow and evaporation had almost equivalent magnitude in driving the lake level variability and direct rainfall had the least influence. Although the lake level variability corresponded to changes in the basin supply components, the declining lake level trend was neither directly related to lake evaporation nor inflow as both parameters showed no significant trends. Furthermore, groundwater abstraction within the lakeshore is smaller than lake evaporation and is unlikely the main driver of the decline in lake level. Therefore, the declining lake level seemed related to the spillway outflow, which had been improved to avoid lake flooding resulting in large outflow during the peak seasons and probably the reason for the significant decline in the lake levels even in the rainy seasons. This study benchmarked the most sensitive hydrological drivers influencing lake level whose accurate monitoring and management could rescue the situation.