Linking Precipitation and Groundwater Recharge in Ethiopia - Implications from Local Meteoric Water Lines and Isoscapes

Abstract:

Stable water isotopes (δ²H and δ¹⁸O) are important indicators of hydrological processes and provide a key foundation for linking climate, precipitation and water resources. A combined spatial analysis of the stable isotope composition of groundwater, surface water and precipitation could help better understand groundwater sources and recharge processes. However, the lack of spatio-temporal water isotope data coverage has been a limitation for the full utilization of this technique in modern and paleo hydrological studies. In this study, we collected 336 groundwater and river water samples across Ethiopia and analyzed their oxygen (δ¹⁸O) and hydrogen (δ²H) isotopes. The isotope data were then interpolated into complete isoscapes for the entire country. These are the first groundwater and river isoscapes for Ethiopia. By comparing the spatial distribution of river and ground isotopes with local precipitation, we grouped Ethiopia into different regions characterized by distinct groundwater recharge patterns in terms of their water source, timing, seasonality, and the degree of evaporation. In addition, at four locations with continuous year-round precipitation isotope data, we found that the groundwater recharge was biased towards the main rainy season. In southeastern Ethiopia, infrequent but high intensity storms associated with tropical cyclones exhibited highly depleted precipitation isotope values. The similarity between the local groundwater and precipitation isotopes associated with the cyclones suggest the importance of extreme events in groundwater recharge. Overall, this study has largely expanded the spatial coverage of water stable isotope data, and filled significant data gaps in the country. Moreover, the outcome could be used to provide vital information in the arid and semi-arid part of the country where water resources are critical component in the climate change adaptation strategies.