Using system dynamics to inform scenario planning: Application to the Souss-Massa basin, Morocco

The watershed represents a holistic system whose poor understanding of its multiple subsystems can lead to a pronounced water scarcity. This study aims to develop an innovative technique for managing water resources within the Souss-Massa watershed. It uses the System Dynamics (SD) methodology to analyze the interplay among the factors involved in water supply and demand. The results show that under the Business As Usual (BAU) scenario, water sustainability in this watershed is not assured. Groundwater drawdown (GWD) will increase significantly, with an estimated average decrease of −337 Mm 3 for the period 2022 to 2050. To remedy this critical situation, several simulations were developed, each representing a distinct scenario. Scenario 1 improves irrigation efficiency by 10%, while scenario 2 achieves a 20% improvement. Scenario 3 builds on scenario 2 by doubling the volume of reused water. Scenario 4 extends scenario 3 by also doubling the volume of desalinated water. Scenario 5 combines the 10% improvement in irrigation efficiency from scenario 1 with a doubling of both reused and desalinated water volumes, along with a stabilization of irrigated areas. Scenario 6 adds a 7% increase in water supply to the measures in scenario 5. Finally, scenario 7 combines the 10% irrigation efficiency improvement from scenario 1 with a doubling of reused and desalinated water volumes, but reduces the irrigated area by 15%. This study is of crucial importance to decision-makers, as it provides them with strategies for promoting water-saving practices and, consequently, advancing the sustainable development agenda. • The study aims to manage water resources in the Souss-Massa watershed using System Dynamics (SD) approach. • The results show that water sustainability is not assured under the “Business As Usual” (BAU) scenario. • Groundwater withdrawals are expected to decrease by 337 ​Mm 3 between 2022 and 2050. • Several scenarios have been developed to cope with water scarcity. • The study provides decision-makers with strategies for promoting water-saving practices and sustainable development.