Groundwater sources in semi-arid regions and their vulnerability to climate change: Drâa catchment, Morocco

Abstract

Water availability in Drâa basin (surface area∼115, 000 km2) depends on rainfall, melting snow in the High Atlas mountains and groundwater. The region has strong evidence of groundwater flow presence whose functioning is required to be fully understood to achieve an adequate water management for an expected rainfall reduction. Previous objectives of carried out studies in the region included the aquifer unit theory and water-balance, lacking a 3D groundwater flow understanding. A regional approach allowing a clearer perspective of groundwater dynamics in its geological context was applied: the Groundwater Flow Systems Theory, which identifies local, intermediate and regional flows hierarchy. The conceptual 3D model included: hydraulic heads, hydraulic properties of rock units, soil type, vegetation, and geomorphology which are in agreement with the physical, chemical and isotopic properties of groundwater. This model was implemented, calibrated and validated using Visual Modflow. Obtained initial-heads were subjected to different recharge conditions; results show that change in recharge is more affecting local flows. However, in the Middle Drâa sub-basin where intermediate flows were identified, the simulated heads lack immediate response to the variation of recharge. Results suggest that local flows are more likely to be affected by climate conditions than those of intermediate and regional nature.