Unravelling the hydrological dynamics of Lake Manyara in Tanzania

Abstract

The catchment of lake Manyara is part of the East African Rift System. It is sensitive to local hydrological changes since it is a closed basin. The Manyara catchment is very important for its inhabitants to provide a sustainable food source. The most dominant types of land use are pastures, rain-fed agriculture and savanna. The most dominant crop types that are cultivated in the area are: bananas, rice and maize. Problems arise since the lake seems to be shrinking during the past 40 years. In this paper possible drivers of the changes in surface area of lake Manyara are studied. The climatological impact on the lake area has been assessed by analysis temperature and precipitation data. In the past 40 years there has been a decrease in precipitation of about 100mm according to the Tanzanian National Parks. The temperature only increased during the dry season with 1.0-2.0°C. Land use changes have been analysed by using satellite imaginary. The images do not show a significant change in land use and are therefore excluded from further analysis. The expected increase in irrigation water abstraction was analysed using the Soil Water Assessment Tool (SWAT) and measurements taken during fieldwork (January-March 2016, Tanzania). It responds quickly to precipitation events. However, it is uncertain if the amount of irrigation water has increased due to a lack of in-situ datasets. The SWAT-model indicates that the event prior to the date of the satellite image is the main driver for the changes in surface area of lake Manyara. There is no reason to believe that Lake Manyara is disappearing. The shrinkage and expanding of the lake has a more cyclic nature. They do not occur on a regular base and the intervals between a small and a large lake seem to be getting longer.