University of Sistan and Baluchestan Journal of Natural Environmental Hazards 2676-4377 15 48 2026 06 22 Synoptic Patterns of Atmospheric Circulation Affecting Widespread Monthly Droughts in the Cold Period of Iran Synoptic Patterns of Atmospheric Circulation Affecting Widespread Monthly Droughts in the Cold Period of Iran 19 44 9195 10.22111/jneh.2025.50956.2105 FA Sousan Heidari PhD in Climatology, Department of Physical Geography, Faculty of Geography, University of Tehran, Tehran, Iran 0000-0002-9749-9025 Mostafa Karimi Associate Professor of Climatology, Department of Physical Geography, Faculty of Geography, University of Tehran, Tehran, Iran Ghasem Azizi Professor of Climatology, Department of Physical Geography, Faculty of Geography, University of Tehran, Tehran, Iran Ali Akbar Shamsipour Associate Professor of Climatology, Department of Physical Geography, Faculty of Geography, University of Tehran, Tehran, Iran Journal Article 2025 02 18 Drought is among the most significant climatic challenges affecting arid and semi-arid regions such as Iran, typically triggered by specific atmospheric circulation patterns. This study aims to identify the atmospheric circulation patterns associated with widespread monthly droughts in Iran, using long-term data from 1979 to 2021 and the ZSI index. The dataset, sourced from the ERA5 reanalysis, includes geopotential height, specific humidity, meridional and zonal wind components, air temperature and monthly precipitation with a spatial resolution of 0.25 degrees. The analysis indicates that widespread droughts do not occur during September, June, July and August. Overall, nine atmospheric circulation clusters were identified with four dominant patterns accounting for over 77% of drought events, emerging as the primary synoptic systems responsible for these occurrences. These patterns include: (1) lower-level subtropical high combined with a mid-level subtropical ridge, (2) lower-level subtropical high integrated with the Siberian high-pressure system with a mid-level ridge, (3) subtropical ridge present at both lower and mid-levels, and (4) lower-level high-pressure system and anticyclone over land. The findings emphasise the significant role of anticyclonic centres, high-pressure systems, and subtropical ridges, mainly active between the Arabian Sea and the Arabian Peninsula, in driving widespread monthly droughts in Iran. The northward shift of these systems relative to the climatological mean results in a marked decrease in precipitation across Iran. Additionally, the spatial configuration of these systems interacts with broader regional and planetary circulation patterns, highlighting the necessity for further research to better understand both monthly and seasonal precipitation variability and the occurrence of extreme drought events. Drought is among the most significant climatic challenges affecting arid and semi-arid regions such as Iran, typically triggered by specific atmospheric circulation patterns. This study aims to identify the atmospheric circulation patterns associated with widespread monthly droughts in Iran, using long-term data from 1979 to 2021 and the ZSI index. The dataset, sourced from the ERA5 reanalysis, includes geopotential height, specific humidity, meridional and zonal wind components, air temperature and monthly precipitation with a spatial resolution of 0.25 degrees. The analysis indicates that widespread droughts do not occur during September, June, July and August. Overall, nine atmospheric circulation clusters were identified with four dominant patterns accounting for over 77% of drought events, emerging as the primary synoptic systems responsible for these occurrences. These patterns include: (1) lower-level subtropical high combined with a mid-level subtropical ridge, (2) lower-level subtropical high integrated with the Siberian high-pressure system with a mid-level ridge, (3) subtropical ridge present at both lower and mid-levels, and (4) lower-level high-pressure system and anticyclone over land. The findings emphasise the significant role of anticyclonic centres, high-pressure systems, and subtropical ridges, mainly active between the Arabian Sea and the Arabian Peninsula, in driving widespread monthly droughts in Iran. The northward shift of these systems relative to the climatological mean results in a marked decrease in precipitation across Iran. Additionally, the spatial configuration of these systems interacts with broader regional and planetary circulation patterns, highlighting the necessity for further research to better understand both monthly and seasonal precipitation variability and the occurrence of extreme drought events. https://jneh.usb.ac.ir/article_9195_0c4f46ff3f6ceb716694c78d1d8cefdf.pdf