This study aimed to evaluate the simultaneous effects of climate change and land use change on the hydroclimatic components of the Dez Dam catchment area, using the semi-distributed SWAT model, CMIP6 climate data, LARS-WG downscaling, remote sensing analysis, and integration with the HEC-HMS model. The Dez basin is highly sensitive to environmental changes due to its semi-arid climate, mountainous topography, dependence on snowmelt, and strategic role in water supply and hydroelectric power generation. The calibration and validation results showed that SWAT has a good ability to reconstruct flow and sediment. Based on the climate scenarios, an increase in minimum and maximum temperatures was predicted in all scenarios, which was the highest in the SSP5-8.5 scenario, and along with a relative decrease in precipitation, it caused a decrease in annual runoff, a decrease in base flow, an increase in evapotranspiration, and a shift in the time of peak runoff to colder months. On the other hand, the land use change scenario with an increase in dryland and barren agricultural lands and a decrease in forest and rangeland covers showed a 54.5% increase in surface runoff, a 17% decrease in aquifer recharge, and a 19% decrease in base flow. NDWI analysis and spatial assessment also indicated a greater sensitivity of the northern and western areas of the basin to runoff and flood generation. Overall, the findings indicate that the Dez Dam basin will face the simultaneous challenge of flash floods and seasonal water shortages, and its management requires vegetation protection, watershed management, and adaptive reservoir exploitation.

Keywords: SWAT, CMIP6, Dez Dam, Climate Change, Land Use

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