Groundwater–surface water interactions and resilience to hydrological extremes in a data-sparse arid transboundary river basin: Insights from collaborative groundwater modelling

Abstract Sustainable groundwater management is key to building resilience to hydrological extremes but remains challenging in data-scarce transboundary river basins. In this study, a transboundary, collaborative, physically based groundwater modelling approach has been developed for the Limpopo River Basin (LRB), which is highly vulnerable to floods and droughts. Monitoring data and model results consistently suggest that prolonged wet periods and floods significantly raised groundwater levels, whereas prolonged droughts decreased them, particularly in the upstream and central regions of the basin characterized by low-storage fractured bedrock aquifers. Groundwater–surface water interactions are greater downstream, where water tables are shallower in unconsolidated superficial materials, and intensify during floods, especially in the central region. Modelling results also suggest that baseflow is less responsive to extremes than groundwater recharge across the LRB, highlighting the groundwater system’s attenuation capacity. The model was subsequently used to assess and discuss a series of co-created management scenarios focused specifically on improving groundwater storage during wet periods for use during dry periods. They included: (1) managed aquifer recharge (MAR), using (1a) injection well(s) next to large dams, (1b) rainwater and runoff harvesting (RRH) and infiltration through local wells, (1c) RRH through local ponds and (1d) small reservoirs (e.g. sand dams); (2) deforestation; (3) afforestation; and (4) increased groundwater abstraction. Scenarios suggest that strategy (1b), when widely applied across the basin, may be the most effective to reduce the risk and impact of floods, droughts, and groundwater depletion by supporting the maintenance of groundwater levels and baseflow, while reducing storm runoff.