Implications for sustainable water consumption in Africa by simulating five decades (1965–2014) of groundwater recharge

Abstract

Groundwater stands as a vital water resource for both present and future generations in Africa. This underscores the importance of examining the sustainability of current groundwater consumption across the continent, along with its capacity to fulfill the current human and essential environmental water needs. Groundwater sustainable yield is a suitable indicator for assessing groundwater sustainability but has not yet been quantified properly across Africa. A thorough quantification of groundwater sustainable yield necessitates a profound comprehension of the spatio-temporal fluctuations in surface hydrology, groundwater recharge, environmental flow, and sectoral water use. In this study, high spatial resolution (10 km) land surface hydrology was simulated for five decades (1965–2014) across Africa by the Community Land Model version 5 at half-hourly time step and aggregated to monthly and annual temporal resolutions. Then, groundwater recharge and environmental flow were quantified based on the water balance approach for the whole continent. Finally, by including African sectoral water use data available for four decades (1971–2010) we obtained the long-term average of groundwater sustainable yield. Based on extensive simulations of long-term land surface hydrology, we discovered that the groundwater system in Africa experienced an average annual recharge of 57.8 mm yr−1 (with a standard deviation of 110.8 mm yr−1 serving as an indicator of spatial variability), corresponding roughly to an annual recharge volume of 1793.6 km3 yr−1. Furthermore, our analysis revealed that the entire continent possesses an annual average potential sustainable yield (with standard deviations) of 4.5 mm yr−1 (10.2), 20.6 mm yr−1 (42.9), and 37.3 mm yr−1 (75.7) under conservative, optimum, and suitable water consumption scenarios, respectively. This calculated annual groundwater sustainable yield corresponds to 141.9 km3 yr−1, 643.1 km3 yr−1, and 1160.5 km3 yr−1 for the conservative, optimum, and suitable scenarios, respectively. Furthermore, the calculated sustainable yield volume is contrasted with the total water storage figures documented for 50 countries throughout Africa. The outcomes illustrate that our calculated annual sustainable yield equates to roughly 0.02%, 0.1%, and 0.17% of the reported groundwater storage across the entire continent. Based on the estimated long-term average sustainable yield and the reported total water storage at the national level, our conclusion is that the accessible groundwater resources could potentially satisfy the current water requirements of both humans and the environment in African countries. This study offers the first model-based estimation of groundwater availability across Africa, potentially serving as a catalyst to inspire further progress toward adopting more sustainable approaches to groundwater usage on the continent.