Corresponding Author: Integrative Approach for Studying Water Sources and Their Vulnerability to Climate Change in Semi-Arid Regions (Drâa Basin, Morocco) (original) (raw)

The Drâa Basin at the south-east of Morocco covers a surface of ~115,000 km , it starts in the High 2 Atlas Mountains and ends in the Atlantic Ocean. Surface water depends on rainfall (stormy events), melting snow and base-flow which help maintaining river discharge during the dry season. The Drâa Basin is characterized by a semi-arid climate with restricted surface water sources. However, this region possesses a relative richness in terms of groundwater flow whose functioning is required to be fully understood to achieve an adequate water management. Previous research in the region included a classical hydrogeology scope (aquifer unit theory and water-balance), which lacks a three-dimensional understanding of groundwater flow functioning. Groundwater represents ~97% of unfrozen freshwater in the continents, so a wide-view regional approach that allows a clearer perspective of groundwater dynamics in its geological context was applied: the groundwater flow systems theory (modern hydrogeology). Thus groundwater flows of different hierarchy (local, intermediate, regional) were identified. Conceptual modelling included both direct (hydraulic head and hydraulic properties of rock units) and indirect data (soil type, vegetation, geomorphology) in agreement with the physical-chemical and isotopic character of water. This model was implemented, calibrated and validated using the Modflow™ package. Initial water-table conditions were simulated during the 1939-1969 period, before construction of the Mansour Eddahbi dam. Obtained initial heads were subject to different recharge conditions representing contrasting climate scenarios. Model simulation reveals that the vulnerability to climate conditions (change in recharge) is related to groundwater flow hierarchy. In the High Drâa Sub-basin where local flows dominate, the water-table shows a difference in head of ~100 m between humid and dry recharge conditions (200 mm/year and 50 mm/year respectively). However, in Middle Drâa Sub-basin where evidence (physical and chemical groundwater properties, soil type and vegetation cover) of intermediate flow was identified, the water-table lacks immediate response to these variable recharge conditions. Results suggest local flows are more likely to be affected by different climatic conditions (recharge) than those of intermediate and regional nature. This knowledge could assist in defining appropriate strategies to manage local flows against drought conditions and to take advantage of intermediate and regional flows which are not directly affected by climatic conditions, but are subjected to concerns on their chemical quality and original recharge zone.