Nivar

Nivar

Synoptic analysis of the role of changes in precipitation patterns ‎in the west and southwest of Iran

Document Type : Original Article

Authors
Professor, Department of Environmental Science, Natural Resources Faculty, University of Tehran, Karaj, Iran
Abstract
Severe variations in precipitation regimes are driven by changes in global atmospheric ‎patterns. Iran, and in particular the western and southwestern regions, are strongly ‎influenced by these changes due to their proximity to the subtropical high-pressure center. ‎The present study aims to examine precipitation variability in western and southwestern ‎Iran from 1989 to 2022. In this study, precipitation patterns in the western and ‎southwestern parts of the country were analyzed by employing composite maps of 850 ‎hPa wind and 500 hPa geopotential height. Data were obtained from the ECMWF and ‎NCEP/NCAR climate databases, and the data analysis was conducted using cluster ‎analysis with a forced fusion method applied to the Euclidean distances of the clusters. ‎The results reveal that in recent years, there have been significant and meaningful shifts in ‎the average position of the subtropical high-pressure ridges and the Mediterranean trough ‎toward higher latitudes, which has facilitated the west-to-east transport of westerly winds ‎toward higher geographic latitudes. This situation leads to a northward shift in the moisture ‎advection pathways into Iran. The frequency of precipitation patterns in the western and ‎southwestern regions of Iran indicates a downward trend over the study period. It should ‎be noted that the results of the event-count analysis do not merely reflect the percent ‎contribution of each precipitation pattern to the whole; in some cases, the number of cases ‎of incoming precipitation to the country is high, yet the mean rainfall amounts are ‎relatively low. Given the meridional displacement of the number of rotating systems ‎entering the country over the study years, a downward trend is observed. Consequently, ‎the east–west redistribution of precipitation patterns toward higher latitudes and the ‎decline in the number of synoptic precipitation patterns crossing the region exert an ‎influence on the overall rainfall in western and southwestern Iran.‎
Keywords
Subjects

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Volume 49, 130-131 - Serial Number 130
October 2025
Pages 195-218

  • Receive Date 11 April 2025
  • Revise Date 30 September 2025
  • Accept Date 01 October 2025
  • Publish Date 23 September 2025