Climate change manifests itself through extreme and unprecedented events. In the temperature variable, these events have increased in the form of heat waves in the world. This study investigates trends in heatwave characteristics across Iran from 1972 to 2023 using daily ERA5 reanalysis data. Our analysis reveals significant upward trends in heatwave frequency, severity, and duration. In most regions, these changes began between 1998 and 2002. The current average number of heatwaves in Iran is 18 per year, representing a 60% increase compared to the start of the study period. The severity of heatwaves has also risen, with average temperatures now exceeding the threshold by 1.8 °C. Copula functions were used to evaluate the probability of simultaneous occurrence of extreme values in the variables of severity, duration and frequency of heat waves. Results show a high likelihood of extreme values occurring simultaneously, particularly for heatwaves with a frequency exceeding 20 events per year, severity above 1.5 °C, and durations lasting 7 days or more. These findings highlight a significant increase in the probability of intense and prolonged heatwaves in Iran. Given these concerning results, there is a growing need for further research to evaluate the potential impacts of heat waves as one of the most critical indicators of climate change in the region.

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