Linking precipitation and groundwater isotopes in Ethiopia - Implications from local meteoric water lines and isoscapes

Abstract

Sustainable water resource management requires a clear understanding of the spatial variation and seasonal recharge of groundwater and their links to local precipitation. A combined spatial analysis of the stable isotope composition of groundwater, surface water, and precipitation could help to understand groundwater sources and recharge processes. In this study, we collected 297 groundwater and stream water samples across Ethiopia and analyzed them for the oxygen and hydrogen isotope ratios. The isotope data were then interpolated into isoscapes for the entire country using the Cokriging method based on their spatial autocorrelation and covariance with elevation, annual mean precipitation, and temperature. These are the first groundwater and stream isoscapes for Ethiopia. By comparing the spatial isotopic distribution of the two water resources with local precipitation, we showed distinct groundwater recharge patterns in different regions in terms of their water sources, timing, seasonality, and the degree of surface and groundwater interaction. We found that the groundwater recharge was generally biased towards the main rainy season. However, in the relatively dry southeastern Ethiopia, groundwater could receive significant input from infrequent high-intensity rainfalls associated with tropical cyclones, but additional precipitation and groundwater isotope data are needed to further test our hypothesis in this data-poor region. Overall, this study has largely expanded the spatial coverage of water stable isotope data and filled significant data gaps in Ethiopia, which could be used to provide vital information in the arid and semi-arid parts of the country where water resources are critical in climate change adaptation strategies.