Impact of climate change on groundwater recharge in lake Manyara catchment

Abstract

This study aimed to estimate the groundwater recharge of the Lake Manyara catchment (7920 km2) in two different time intervals, historical 1988-2018 and near-future 2021-2050 climatic condition. This study analyzed the trends, spatio-temporal variability in rainfall and temperature, and the length of the rainy season (LRS) in the Lake Manyara catchment, Tanzania covering a period between 1988 and 2018 using stations and satellite climate product. The Mann-Kendall statistical test, Sen‘s slope estimator and inverse distance weighting interpolation techniques were used to detect the trends, magnitude of trends and spatial distribution of rainfall and temperature. A modified Stern‘s method and water balance concept were used for rainfall onset, cessation and LRS analysis while standardized precipitation index (SPI) was used to investigate the wetness or dryness of the area. Then Coordinated Regional Downscaling Experiment output (CORDEX) Africa data rainfall and temperature projections obtained and lastly used as input data in the WetSpass model for groundwater recharge estimation. The results showed high variability and decreasing trends (4 mm/y) in annual rainfall and non-significant increasing trend for minimum and maximum temperature. The WetSpass results showed historical mean annual recharge of the catchment was 53.9 mm/y with the potential groundwater recharge of 149 Million Cubic Metre (MCM). The results of projected recharge estimated to be 88.5 mm/y with the potential groundwater recharge of 421 MCM. Statistically the contribution of the historical rainfall to the groundwater recharge was 6.7% compared to 8.1% in the projected period. However, the most potential recharge zones in the catchment identified around the northern part (around Ngorongoro), western and southwestern (Buger ward and Mbulu). There is a need, therefore, for adaptation measures such as improving water productivity and irrigation at the farm and catchment level.