Groundwater–Surface Water Interactions in Ethiopia: A Review of Knowledge Gaps, Emerging Opportunities, and the Role of Integrated HydroGeoSphere Modeling under Climate Change

In climate-vulnerable and data-scarce countries like Ethiopia, developing an understanding of groundwater–surface water (GW–SW) interactions is essential to understanding hydrological and hydrogeological functioning, ecological resilience, water security, and sustainable water resource management. Water resources in Ethiopia support rain-fed and irrigated agriculture, domestic supply, urban centers, hydropower, and water-dependent ecosystems. Current understanding of GW–SW processes in Ethiopia is fragmented, with most existing groundwater and surface water studies conducted independent of one another. The result is substantial knowledge gaps pertaining to effects of widespread irrigation, land-use change, and climate change on connected water systems, capacity of aquifers during droughts, and seasonal GW–SW exchange fluxes and GW contribution to stream flow.  A literature  analysis of GW–SW interactions in Ethiopia highlights methodological and scientific limitations, and indicates opportunity to improve GW–SW understanding through fully-integrated GW–SW modeling. GW–SW interaction investigations in Ethiopia are primarily local and clustered geographically. The dynamic feedbacks between surface water, unsaturated zones, and aquifers are still not well quantified, with most studies relying on point-scale hydrogeochemical indicators, baseflow separation methods, or groundwater potential mapping. Predictive understanding hydroclimatic datasets and hydrogeological processes is limited by lack of long-term monitoring data, inconsistent conceptual models, and minimal representation of land-use change and unknown human water abstraction.  There are no fully-integrated GW–SW modeling studies at a basin/watershed scale in Ethiopia, although loosely coupled models have been used.  As part of a Natural Resources Canada Technical Assistance Program with Wollo University, a HydroGeoSphere fully-integrated GW–SW model for the Borkena watershed, located on the northeastern margin of the Rift Valley, has been created for educational and training purposes. The development of the HGS model followed the framework laid out in the Canada1Water initiative for national scale water resources assessment. As part of the model construction process, requisite data has been assembled from globally extensive sources, including geology, hydrology, soil, landcover and vegetation, and climatology; thus demonstrating that state-of-the-art models can be deployed in perceived data sparse regions. Following construction, model application can be demonstrated towards long-term water security planning, climate resilience, and sustainable water management in Ethiopia. The framework developed in this project is broadly applicable to other Sub-Saharan African nations, where process-based understanding of GW–SW interactions is indispensable but still lacking.