Assessment of the Climate Change Impact on the Past and Future Evapotranspiration and Flows from a Semi-arid Environment

Ensuring access to potable water for a substantial portion of the population, effectively managing and conserving this frequently overutilized resource, regulating agricultural and industrial water consumption, and safeguarding the natural environment constitute significant challenges, particularly in the context of developing nations. The primary objective of this investigation was to assess the influence of climate change on the hydrological patterns within the Essaouira basin during the time frame of 2020–2050. To accomplish this, the Rural Genius GR2M model was employed to simulate streamflows based on precipitation and evapotranspiration data. The Mann–Kendall and Pettitt tests were employed to scrutinize the temporal series for both their consistency and directional trends. The chronological sequence of potential monthly evapotranspiration (ETP), covering the span from 1978 to 2005, demonstrates an escalating tendency, denoting a 4.2% increase. This trend in potential evapotranspiration remains evident under different Representative Concentration Pathways (RCPs) of CMIP5 (Coupled Model Intercomparison Project Phase 5) scenarios, specifically 2.6, 4.5, and 8.5 RCPs, where the trend rates are measured at 1.9%, 1.5%, and 1.6%, respectively. The investigation into the correlation between precipitation and streamflows, from 1978 to 2005 within the Essaouira basin, establishes the presence of a causative relationship between these two variables. This relationship holds true across all regions subject to arid and semi-arid climatic conditions. The insights derived from these findings can provide a foundation for safeguarding and managing water resources within the Essaouira watershed, including the construction of upland reservoirs along the Igrounzar, Zelten, and Ksob Wadi, enhancing the basin’s overall water management strategy.