Intensifying heatwave trends in Iran based on observational data using excess heat factor (EHF)

This research investigates heatwaves spatiotemporal variations, their decadal trends, and aspects in different climate zones over Iran. The mean daily maximum temperature and the mean daily minimum temperature from 49 ground stations covering 40 years (1981–2020) were collected. Using excess heat factor, we computed five heatwave aspects, including heat wave number (HWN), heat wave frequency (HWF), heat wave duration (HWD), heat wave magnitude (HWM), and heat wave amplitude (HWA), over different climate zones of Iran. The result showed that the average HWN, HWF, and HWD had been about 2.5 events, 12 days, and 6 days/year, respectively. The findings highlight that distinct climate zones may have different heatwave responses within the country. The maximum HWN observes in the eastern and southwestern parts of the country due to the higher sensible heat flux over these regions. The maximum HWM is seen in the northwest, northeast, and mountainous regions. The high values of the HWA are seen in the northwest due to the more significant positive temperature anomaly in this region. This result emphasizes the latitudinal effect of local climatology in the HWA and HWM variations. The findings show that all heatwave aspects, especially HWF and HWD, have increased rapidly in the recent decade (the 2010s) compared to previous decades in different climate zones. The heatwave trend showed that HWN and HWF increased in 87.75% of the country and HWD and HWA increased in 73.46% and 71.42% of the country, respectively.