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<p>By analyzing extreme rainfall trends across two distinct periods (1960–1990 and 1991–2021), this study identifies long-term patterns of change in Iran’s climate. Data from 36 meteorological stations, selected to represent diverse climatic regions across the country, were analyzed using extreme value theory. A generalized extreme value distribution was fitted to the extreme rainfall data, and return levels were estimated at the 5%, 50%, 75%, 95%, and 99% percentiles. We further calculated quantitative changes in return periods and intensities to assess whether the frequency and magnitude of extreme rainfall events have shifted significantly. Results indicate that rainfall extremes have changed between the two periods, though not uniformly across regions. Northern and eastern stations show a consistent decrease in return levels (average reductions of 8–15%), while western regions exhibit increases (average rises of 10–18%). These findings highlight spatial heterogeneity in rainfall extremes and emphasize the importance of considering both temporal and regional scales when assessing climate change impacts in Iran.</p>

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Non-stationary frequency assessment of return levels and percentiles changes of extreme rainfall under climate change in Iran

  • 期刊论文

  • 发表日期：

    2026年4月17日

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  • M. Razi Ghalavand,
  • M. Farajzadeh,
  • Y. Ghavidel Rahimi

摘要

By analyzing extreme rainfall trends across two distinct periods (1960–1990 and 1991–2021), this study identifies long-term patterns of change in Iran’s climate. Data from 36 meteorological stations, selected to represent diverse climatic regions across the country, were analyzed using extreme value theory. A generalized extreme value distribution was fitted to the extreme rainfall data, and return levels were estimated at the 5%, 50%, 75%, 95%, and 99% percentiles. We further calculated quantitative changes in return periods and intensities to assess whether the frequency and magnitude of extreme rainfall events have shifted significantly. Results indicate that rainfall extremes have changed between the two periods, though not uniformly across regions. Northern and eastern stations show a consistent decrease in return levels (average reductions of 8–15%), while western regions exhibit increases (average rises of 10–18%). These findings highlight spatial heterogeneity in rainfall extremes and emphasize the importance of considering both temporal and regional scales when assessing climate change impacts in Iran.