Assessing hydrological response to future climate change in the Bouregreg watershed, Morocco

Hydrological systems in watersheds encounter growing challenges attributed to climate change, marked by shifts in precipitation patterns, heightened drought severity, and altered runoff dynamics. This study explores the implications of these changes for streamflow in the vulnerable Bouregreg catchment. This study used a novel approach in the Bouregreg watershed to address this issue by applying the underutilized GR2M model, deviating from the prevalence of ArcSWAT and other models in previous studies. It incorporates bias-corrected outputs from the CNRM-CM5 climate model, sourced from the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP). The objective was to project monthly streamflow for the 2040s (2030-2050) and compare it with the reference period (1982-2001), considering the Representative Concentration Pathways (RCPs): medium RCP4.5 and high RCP8.5. The methodology started with predicting future precipitation and temperatures using the regional climate model. Then, the future average rainfall for each subbasin was determined using the Thiessen method, and the future potential evapotranspiration (PET) was estimated through the Thornthwaite formula, considering the model-predicted temperatures. Following this, the hydrological model was calibrated and validated, leading to streamflow projection for the 2040s period under the two emission scenarios. The choice to utilize climate models and hydrological modeling techniques was driven by the need to provide valuable insights for water resource management. By projecting future streamflow under different emission scenarios, the study aimed to inform decision-makers about the potential impacts of climate change on water resources. The study's findings revealed that significant climatic changes would occur in the Bouregreg catchment under the RCPs. Projections indicated a noticeable increase in mean temperatures, with expected rises of about 1.32 degrees C for RCP4.5 and 1.69 degrees C for RCP8.5. Additionally, the PET is foreseen to rise by 5.38 mm under RCP4.5 and 6.27 mm under RCP8.5, while precipitation levels are anticipated to experience significant reductions, decreasing by 33.74% for RCP4.5 and 40.20% for RCP8.5. These pronounced climate alterations are projected to lead to an annual decrease in streamflow. For RCP4.5, this reduction is estimated at 44.63%, and for RCP8.5, it is even more significant at 64.30%. The alterations projected for the 2040s signify a substantial departure from the conditions observed during the reference period of 1982-2001.