Analysis of the Trend and Spatial Variation of Aridity in the Future Climate of Iran

This research aims to investigate the spatial variability and temporal trends of Iran's aridity in the future (2020–2050) based on the SSP2-4.5 and SSP5-8.5 scenarios of CMIP6 models (MRI-ESM2 and GFDL-ESM4) compared to observational data (1992–2014) using AI and IDM indices based on precipitation, evapotranspiration, and average temperature variables. The coefficient of variation and innovative trend analysis were exerted to examine the changes and trends of the average annual aridity, respectively. The results showed that during the observation period, except for the northern areas of Alborz and a part of the northwest, other areas of the country were arid and semi-arid. However, in the future, the scenarios show a decrease in humidity in the northern areas of Alborz, the northern areas of the inner plateau of Iran, and parts of the southern areas of the Zagros mountains. Aridity decreases in the northwest and parts of the central and northern regions of Zagros. The models predicted arid and semi-arid conditions in other areas, as in the past. The highest percentage of annual average spatial variation of land (71%–105%) was observed in the southeast and south coasts of the country in the period 1992–2014, and according to the models, the percentage of spatial variation of land will decrease in the future. The trend of the average annual aridity values of Iran showed that the drought has increased at significance levels of 0.05 and 0.01 in the past and will increase in the future at significance levels of 0.05 and 0.01 based on MRI-ESM2 (SSP5-8.5 scenario and IDM index). At these significant levels, aridity shows a decreasing trend in other conditions. The results of this research can be useful in planning and reducing the negative effects of climate change in Iran.