Analysis of Monthly Precipitation and Temperature Anomalies in Iran and Their Association with Atmospheric Circulations during Autumn and Winter 2024-2025

Iran, situated within arid and semi-arid regions due to its geographical and general atmospheric circulation characteristics, has experienced intensified climatic extremes over recent decades. Extreme temperature variability and erratic precipitation patterns define these zones, but the past two decades have witnessed unprecedented drought frequency, severity, and spatial extent. The autumn and first half of winter 2024–2025 stood out as exceptionally dry and warm, as revealed in this study.

Utilizing monthly data from 179 synoptic stations spanning 1951 to February 2025, alongside NCEP/NCAR reanalysis datasets (including sea-level pressure, geopotential heights at 850 mb, 700 mb, 500 mb, and 200 mb, and 200 mb wind components), this research calculated annual climatic indices for precipitation and temperature. Five-month averages (October–February) were analyzed to assess trends across two periods: 1951–2024 and 1991–2024. To evaluate the anomalous conditions of 2024–2025, monthly temperature and precipitation data were chronologically ranked within these sequences, and a spatiotemporal variation was derived by comparing station-level deviations against long-term averages.

Composite maps of monthly sea-level pressure and geopotential height, stratified into three layers (1991–2020 climatic averages, Study period (October 2024-February 2025), and anomalies), were analyzed alongside 200 hPa jet stream dynamics. This approach identified spatial shifts in high/low-pressure systems and alterations in jet steam patterns, elucidating how atmospheric dynamics influenced nationwide precipitation and temperature distributions.

The analysis revealed pronounced climatic shifts during autumn and winter 2024–2025. Precipitation Changes (PC) ranged spatially from -91.27% to +40.37%, with 90% of stations reporting negative deviations.

Monthly negative PC exceeding -50% thresholds affected 70% (October), 81% (November), 95% (December), 94% (January), and 71% (February) of stations. Concurrently, 79% of stations recorded temperature increases, peaking at +2.05°C in November 2024. The five-month average temperature exceeded climatic norms by +1.8°C, with January 2025 and November 2024 exhibiting maximum warming, while February 2025 showed relative cooling.

These anomalies correlated with Northern Hemisphere atmospheric shifts. The Icelandic Low (strengthened except in November [+13 mb]) and Aleutian Low (intensified in December/February [-13 mb over the North Pacific] but weakened in October/January [+13 mb over the eastern Pacific and western U.S.]) interacted with Siberian, Azores, and Canadian Highs under meridional anomaly regimes. Persistent geopotential ridges extended from Northwest Africa to Western Europe and Greenland, accompanied by positive anomalies over Europe and North America. This pattern intensified in January 2025, the third-driest month in 74 years, with amplified ridges over the eastern North Pacific, eastern Atlantic jet stream, and Indian subcontinent. The November 2024 subtropical ridge expansion from the Bab-el-Mandeb Strait to Northern Iran (+500 hPa anomalies) resulted in the second-hottest month on record.

The clockwise rotation of the North Atlantic Jet Stream axis (shifted from SW-NW to W-E) induced severe contour gradients south of the Icelandic Low, enhanced westerlies over the southwestern North Atlantic and 20ºN–35ºN latitudes, and suppressed Mediterranean transient eddies, collectively reducing precipitation over Iran. The convergence of long-term trends (declining precipitation and persistent warming) with anomalous atmospheric patterns has exacerbated aridity and temperature extremes across the Middle East, underscoring the compound impacts of climate change and atmospheric variability on regional hydroclimatic regimes.