Evaluation of the impact of large-scale atmospheric indicators and meteorological variables on drought in different regions of Iran

Iran experienced increasing droughts in recent years. Since droughts have devastating effects on the economy and irreparable impacts on the environment, knowing the factors affecting droughts can effectively help their early warning and loss reduction. The present study used Palmer Drought Severity Index (sc-PDSI) and large-scale atmospheric indices (ENSO, IOD) to examine how various factors affected drought (precipitation, temperature, evapotranspiration, VPD, NDVI) in eight regions of Iran from 1981 to 2020. Results revealed that the northwest and southeast of Iran experienced longer duration and more severe droughts in the last 40 years. There is an increase in annual total precipitation and average daily temperature in all regions of Iran. The vegetation cover has changed slightly; however, its density has increased on the Caspian Sea shores due to increased rainfall. Correlation analysis revealed ENSO as Iran's primary driver of droughts, while the IOD affects sc-PDSI only in the central plateau. Besides, the ENSO significantly affects the vegetation changes in Iran. General trends in precipitation, temperature, evapotranspiration, VPD, NDVI, and sc-PDSI indicate northwest Iran as most prone to drought.