The shrinkage of Lake Manyara: causes and management options for lake protection

Abstract

Lake Manyara is a terminal soda lake in the East African Rift System in Northern Tanzania, which provides an important habitat for flora and fauna in the area. Its size also reflects the water availability in the catchment, which is of great importance for local human inhabitants and wildlife. Lake levels naturally fluctuate over the year, but they have been following a shrinking trend in the past decades. The factors that contribute to the shrinkage of the lake have been researched in several studies, but the cause of the shrinkage remained unknown. The aim of this research was to unravel the causes of the shrinkage of Lake Manyara and to discuss management options that best guarantee a sustainable future for the lake. A literature review was carried out to determine which factors contribute to the shrinkage of Lake Manyara. Results strongly suggest that both the use of irrigation water and changes in land use and land cover have neglectable impacts on the shrinkage of the lake. The combination of precipitation and evapotranspiration seems to have a large impact on the size of Lake Manyara. Future rainfall is uncertain because of the East African Climate Paradox, but temperatures in the area will almost certainly increase in the coming decades. Increasing temperatures will lead to increased amounts of evapotranspiration and enhanced periods of droughts. This will almost certainly cause a decreasing size of Lake Manyara in the coming decades, mainly in the dry season. To determine the contribution of gully erosion to the shrinking lake levels, a remote sensing study based on images from Google Earth Pro was performed. Sedimentation in Lake Manyara does occur as a result of gully erosion, but the contribution of sediment load to the shrinkage of the lake is minor when compared to climatological changes. Management strategies that could enhance environmental rehabilitation help to adapt to drought conditions were discussed. It was shown that socioeconomical factors should be taken into account when selecting measures, since the success of proposed measures largely depends on them. The implementation of local measures will have a positive impact on the environment and the livelihoods of humans in the catchment. Local measures will however not prevent the shrinkage of Lake Manyara, since anthropogenic climate change is by far the largest contributor to its shrinkage.