Detection of heat waves in the Zagros decline monitoring sites In Chaharmahal and Bakhtiari province

Today, oak decline is one of the most important challenges facing the Zagros forest ecosystem. The phenomenon of decline is affected by various natural and human factors. Among the natural factors, heat waves have emerged as a consequence of climate change during the last two decades and have contributed to the decline of Zagros forests. In order to reveal the effect of heat waves on the decline of Zagros forests in Chaharmahal and Bakhtiari province, the most important characteristics of heat waves including frequency of day with hot wave, number of hot wave events and continuity of hot waves in four Zagros decline monitoring sites were studied. Daily data from the nearest synoptic stations to the decline sites were used for a complete climatic period from1991 up to 2019. The wave features were calculated using ClimPACT software in R 2.10 programming environment. The year of onset of heat wave at the sites of decline and trend changes and trend slope error and significance of changes were extracted with P-value = 0.05. The results showed that all heat wave indices in all decline monitoring sites had an increasing and significant trend. The frequency index of the day with hot wave in Chigo and Ghale Sama monitoring sites started from 7 days with hot wave and reached 39 days in 2019. At Gel Sefid and Rahimaabad sites, 10 days with a hot wave in 2005 reached 38 days in 2014. The highest frequency of hot events at the sites of Chigo and Ghale Sama was six events in 2015. In sites of Gel Sefid and Rahimaabad, the highest number of hot wave events with seven events was in 2014. Examination of the frequency index of hot wave occurrence in the two declined sites of Chigo and Ghale Sama showed that the highest continuity of hot wave occurrence was for 32 days in 2018. In the two declined sites of the Gel Sefid and Rahimaabad, the highest continuity of the hot wave occurred in 2018 and lasted for 14 days. Comparison of hot wave characteristics between declined monitoring sites showed that in Chigo and Ghale Sama, located at a lower latitude, all heat wave characteristics were more intensive. Considering the increasing trend of global warming and the location of Zagros forests in Chaharmahal and Bakhtiari province, it is expected that in the future the number of hot wave days, the number of hot wave events and the continuation of heat waves will continue with greater intensity, therefore managers and decision makers must adopt strategies to these changes in order to preserve the ecosystem