University of Sistan and Baluchestan Journal of Natural Environmental Hazards 2676-4377 Articles in Press 2025 06 06 Analysis of changes in the frequency of maximum temperatures in Iran Analysis of changes in the frequency of maximum temperatures in Iran 1 1 9221 10.22111/jneh.2025.51939.2114 FA Farahnaz Khorramabadi PhD student of Climatology, Faculty of Geographical Sciences and Planning, University of Isfahan, Iran Mohammad Sadegh Keikhosravi-Kiany Assistant Professor of Climatology, Faculty of Geographical Sciences and Planning, University of Isfahan, Iran Seyed Abolfazl Masoodian Professor of Climatology, Faculty of Geographical Sciences and Planning, University of Isfahan, Iran 0000-0001-6227-6713 Journal Article 2025 05 06 In recent years, there has been a notable increase in the intensity and frequency of extreme temperatures, encompassing both extreme heat events—such as hot days, hot nights, and heat waves—and extreme cold events, including cold days and cold nights. This study analyzes changes in the frequency of maximum temperatures in Iran utilizing daily temperature data from the Era5 database, covering the period from 11/10/1357 to 10/10/1402. Following the year 1377, the frequency distribution of maximum temperatures exhibited a notable shift towards higher values, accompanied by a reduction in seasonal temperature differentiation. This transition resulted in a change in the temperature distribution from a biexponential to a uni exponential model, as well as an increase in leftward skewness within the temperature distribution. The frequency of 37 degrees Celsius experienced the most significant increase, recorded at 0.5 percent, while the frequency of 1 degree Celsius demonstrated the most substantial decrease, exceeding 0.3 percent. These observed changes may be attributable to local factors, such as urbanization and desertification, as well as broader influences stemming from global climatic phenomena, including significant El Niño events. An examination of the thickness of the 850-500 hectopascal layer indicates that the spike in maximum temperatures in Iran in 1998 is not merely a localized occurrence but rather a manifestation of global climate change that has disrupted the previous climatic equilibrium. These changes indicate the widespread and continuous effects of global warming on the climate of Iran and beyond In recent years, there has been a notable increase in the intensity and frequency of extreme temperatures, encompassing both extreme heat events—such as hot days, hot nights, and heat waves—and extreme cold events, including cold days and cold nights. This study analyzes changes in the frequency of maximum temperatures in Iran utilizing daily temperature data from the Era5 database, covering the period from 11/10/1357 to 10/10/1402. Following the year 1377, the frequency distribution of maximum temperatures exhibited a notable shift towards higher values, accompanied by a reduction in seasonal temperature differentiation. This transition resulted in a change in the temperature distribution from a biexponential to a uni exponential model, as well as an increase in leftward skewness within the temperature distribution. The frequency of 37 degrees Celsius experienced the most significant increase, recorded at 0.5 percent, while the frequency of 1 degree Celsius demonstrated the most substantial decrease, exceeding 0.3 percent. These observed changes may be attributable to local factors, such as urbanization and desertification, as well as broader influences stemming from global climatic phenomena, including significant El Niño events. An examination of the thickness of the 850-500 hectopascal layer indicates that the spike in maximum temperatures in Iran in 1998 is not merely a localized occurrence but rather a manifestation of global climate change that has disrupted the previous climatic equilibrium. These changes indicate the widespread and continuous effects of global warming on the climate of Iran and beyond https://jneh.usb.ac.ir/article_9221_66fac18653778a11aafad5564dd8c15f.pdf