Abstract
The Arabian Peninsula (AP) has been reported to experience increasing drought in recent decades. With this background, this study evaluates best performing Climate Model Intercomparison Project 6 (CMIP6) Global Climate Models (GCMs) for historical (1985-2014) simulations and future drought projections across the AP until 2100, using the standardized precipitation index (SPI) and standardized precipitation-evapotranspiration index (SPEI). We assess uncertainties from model differences, scenarios, timescales, and methods. Our findings reveal the limitations of most models in reproducing precipitation, leading to uncertainties in SPI projections. Nonetheless, CMIP6-GCMs better capture the increase in the current-day potential evapotranspiration (PET) and therefore the SPEI, which is dominated by PET. The Hargreaves based PET is identified as the most suitable method for SPEI projections. The rate of increase in PET surpasses that of precipitation in all scenarios by fivefold. Consequently, SPEI indicates projected increase in future droughts with greater changes in SSP585 and SSP370 scenario compared to SSP245 and SSP126. In general, drought will exacerbate in the AP despite uncertainties from indices selection, scenarios, and inter-model variability, followed by methods and timescales which predominantly impacts drought magnitude. Over findings emphasize the need for more reliable representation of the AP precipitation in climate models for improved drought projection over the AP to enhance planning and adaptation strategies.