Climate Change in Jordan: A Case Study of Yarmouk Basin Using Statistical Downscaling Model

This study evaluates the impacts of climate change in the Yarmouk River Basin (YRB) using the Statistical Downscaling Model (SDSM) and observed data from six meteorological stations (1989-2017). The second-generation Canadian Earth System Model (CanESM2) was used to project climate scenarios under Representative Concentration Pathways (RCPs) for the period 2018-2100, demonstrating strong performance in modeling the arid climate (R2 = 0.87-0.996, RMSE = 0.478-1.829 for calibration; R2 = 0.799-0.998, RMSE = 0.55-1.879 for validation). Projected maximum temperature increases across the basin range from 0.19 degrees C to 1.8 degrees C, while minimum temperature rises from 0.096 degrees C to 1.4 degrees C, depending on emission scenarios. Precipitation is expected to decline by 3% to 49%, with the most severe reductions under RCP8.5. Moreover, current climate observations indicate sharper temperature increases and precipitation declines than even RCP8.5 projections, signaling elevated risks of drought and water scarcity. The analysis of extreme events reveals substantial increases in heatwaves, notable declines in cold spells, and longer dry periods across all scenarios. Under RCP8.5, heatwave days may rise by up to 22, cold spells may drop by more than 24 days, and consecutive dry days could extend by over 65 days, suggesting intensified drought stress. A frequency analysis of the 12-month Standardized Precipitation Index (SPI-12) reveals relatively stable hydro-climatic conditions under RCP2.6, with a balanced distribution of dry and wet months and minimal extremes. Under RCP4.5, a modest shift toward drier conditions emerges, with slightly increased drought frequencies and minor extreme events. In contrast, RCP8.5 projects pronounced drying, with over 40% of months falling below SPI = -0.5 in Irbid and Al-Mafraq, and rising frequencies of both extreme drought and wet months in Samar. These progressive changes highlight the basin's vulnerability to emission-driven climate impacts and underscore the urgent need for adaptation planning. The findings support the SDSM-CanESM2 framework as a robust tool for assessing climate risks and guiding mitigation strategies in arid and semi-arid regions.