Abstract
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 °C to 1.8 °C, while minimum
temperature rises from 0.096 °C to 1.4 °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
