High-resolution spatiotemporal analysis of drought dynamics in Iran

High-resolution data can help us better understand the patterns and temporal variations related to drought. This research examines drought trends in Iran utilizing the self-calibrated Palmer drought severity index (scPDSI) and high-resolution TerraClimate data (4 km resolution) from 1958 to 2022. Based on the scPDSI index, a total of 558 drought occurrences were identified. Drought migration distance showed a decreasing trend (- 42.135 km/year), indicating that droughts are becoming more stationary, intensifying local impacts. Conversely, drought duration and affected area increased (0.0767 month/year and 41,055 km²/year, respectively), suggesting longer-lasting and more widespread droughts. On the interdecadal scale, the drought magnitude demonstrated a cyclical pattern of increase-decrease-increase from 1958 to 2022. For the most severe drought event, from February 2021 to December 2022, the starting and ending places were in the east, northwest, and then in the middle of the country, respectively. The movement or migration direction was more clockwise, roughly along with the direction of east to northwest and then east. This analysis shows that the distribution pattern of drought throughout the year has changed according to different seasons and months, and the spring and winter seasons are more severe. In recent decades, the most severe drought clusters-based on scPDSI-have been primarily concentrated in the west, northwest, and the central Alborz. However, previous studies using other indices (e.g., SPEI) have also highlighted southeastern and central Iran as highly vulnerable to extreme droughts. Observations indicate that moderate to severe droughts have significantly increased, such that since 1999, the scPDSI index has frequently dropped below threshold - 2 in most years, indicating the persistence of moderate, severe, and extreme droughts across the country.