Impact of Climate Change on Groundwater Resources of the Atankwidi Basin in Ghana, West Africa
Agbenorhevi, Albert Elikplim
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The Atankwidi basin is a sub-basin of the Volta River basin, which is located in West Africa. It is a transboundary basin shared by Ghana and Burkina Faso and has a drainage area of about 286 km2. The basin dwellers depend heavily on groundwater sources abstracted through boreholes and hand-dug wells for domestic water supply, dry season irrigation of vegetables, livestock watering and limited industrial activities. However, considering the discrete nature of groundwater in the basin coupled with changing climate, increasing population, and expansion in irrigation activities, it is unclear how future water demands will impact on the groundwater resources. The study utilized a modelling approach to assess the impacts of climate change and future abstraction scenarios on the groundwater resources of the Atankwidi basin, with the aim of contributing to sustainable management of the basin’s groundwater resources. The approach consisted of adapting a groundwater modelling software (GMS 10.3- MODFLOW) to the study basin to simulate the groundwater system including groundwater levels and driving the adapted groundwater model with estimated future recharge and water demands to quantify their impacts on the groundwater system. The future recharge estimate was obtained from outside of this study as input. It was developed using the Soil and Water Assessment Tool (SWAT) and four future climate projections driven by the medium low-end and high-end IPCC emission scenario, RCP4.5. and RCP 8.5. The reference period for the study was set to 1986-2010 while the future horizon was set to 2051-2080. The future water demands were estimated based on a population growth rate of 1.1% between 2010 and 2080; an increase in per capita water consumption from 35 l/c/d to 50 l/c/d and 55 l/c/d to 110 l/c/d for the rural and urban population, respectively; and a doubling of the cropping intensity for irrigation. Three future scenarios were analyzed. Scenario 1 (recharge only scenario) considered changes in recharge between 2010 and 2080 while demands remain unchanged; scenario 2 (demands only scenario) considered changes in water demands but no change in recharge; and scenario 3 considered changes in both recharge and water demands. Based on projections of temperature and rainfall analyzed over the Atankwidi area, the basin is going to be likely warmer (5.2 °C to 6.5 °C) and slightly wetter (-0.53 % to +7.7 %). The recharge in the basin experienced a decrease by 6.2% under RCP 4.5 (2051-2081) relative to (1986-2010) but will increase slightly above the baseline to a region of 7.3%. Water demand in the basin is estimated to increase by 76.5% relative to the baseline as 40.7% of the demand coming from the agricultural sector, 39.5% from domestic demand and 19.8% from industrial. Scenario 1 showed an up rise of water table by 1747.08m3/d under RCP 8.5 but a slightly decrease by RCP 4.5. Scenario 2 impact on the basin resulted in a stress on the water table leading to more drilling of boreholes due to 76.5% increase in demand. Scenario 3 showed a significant impact of drawdown of the water table when recharge is coupled with future demand. These results are vital for a sustainable groundwater management in the Atankwidi basin and larger extent the White Volta Basin. But further research must be carried out for a best decision support system to be established for Atankwidi.