Seasonal analysis and trend of heat stress in Iran using ERA5 data

Document Type : Research Article


1 Department of Geography, Faculty of Humanities & Social Sciences, Yazd University, Yazd, Iran.

2 Department of Geography, Faculty of Dr. Ali Shariati Letters and Humanities, Ferdowsi University of Mashhad, Mashhad, Iran.


To assess thermal comfort of residences, several different factors as meteorological, physiological, and socio-cultural, should be considered. The integrated effect of these variables on thermal stress can be obtained and evaluated using thermal comfort indices. Thermal comfort as a bio-meteorological index is of special importance. The purpose of this research is to analyze the seasonality and trend of heat stress in Iran in the period from 1981 to 2020. In this research, the Universal Thermal Climate Index (UTCI) index as a common thermal index was evaluated for outdoor thermal comfort, using ERA5 dataset. ERA5 is the fifth generation ECMWF reanalysis data for the global climate and weather for the past 4 to 7 decades. The ERA5 provides hourly estimates for a large number of atmospheric, ocean-wave, and land-surface quantities. An uncertainty estimate is evaluated by an underlying 10-member ensemble at three-hour intervals. Such uncertainty estimates are closely related to the information content of the available observing system which has improved considerably over time. They also indicate flow-dependent sensitive areas (Hersbach et al., 2020). Also, root mean square error (RMSE), Percent bias (PBIAS), Nash–Sutcliffe model efficiency coefficient (NSE), and Root Mean Standard Deviation Ratio (RSR) metrics were used to evaluate the quality of ERA5 dataset.
The seasonal variability of the UTCI index shows that this index has significant regional heterogeneity in Iran. The increase in UTCI from the north to the south of Iran leads to an increase in thermal stress. The spatial distribution of areas that do not have thermal stress during the hot period of the year are mainly consistent with the altitudes. During the cold seasons of the year, areas with elevations of more than 3,000 meters in Iran have moderate cold stress. The investigation of the trend of thermal stress during the last four decades, which was analyzed with the modified Mann-Kendall test, shows that the UTCI in Iran has a dominant increasing trend. The UTCI index shows an increasing trend in the spring and autumn seasons by 100%, and in the winter and summer seasons at 99.83 and 99.75% of the country, respectively. The maximum significant increasing trend of the index at the level of 0.05 was achieved in the spring. In the same way, the highest value of Sen's slope estimator test of the area-averaged trend is also seen with the value of 0.52 oC in this season in the study period. The results of this study for climatology and the trend of the UTCI index in Iran show that: 1- There is a close relationship between heat and cold stresses in Iran and topography, but this relationship is not a linear; 2- Along with global warming, the UTCI index in Iran during the years 1981-2020 has shown an increasing trend; 3- In general, areas with UTCI cold stress in the country are decreasing and areas with heat stress are increasing; 4- One of the key findings in this study is the significant increase in trend of the UTCI index in the spring season.


Main Subjects

احمدی، م.؛ اسدی، م. و داداشی رودباری، ع. (1395). تعیین تقویم آسایش حرارتی شهر سبزوار با استفاده از شاخص‌های دمای معادل فیزیولوژی (PET) و متوسط نظر پیش‌بینی‌شده (PMV)، فصلنامه جغرافیایی فضای گردشگری، 5(19)، 41-58.
اسدی رحیم‌بیگی، ن.؛ زرین، آ.؛ مفیدی، ع. و داداشی رودباری، ع. (1400). تحلیل پراکنش فصلی بارش‌های فرین در ایران با استفاده از پایگاه AgERA5. مجله تحقیقات آب و خاک ایران، 52(11)، 2723-2737.
باعقیده، م.؛ شاکری، ف. و میوانه، ف. (1396). بررسی مقایسه‌ای تنش‌های حرارتی در سواحل شمال و جنوب ایران. مجله تحقیقات سلامت در جامعه، ۳(۳)، 1-11.
زرین، آ.؛ داداشی رودباری، ع. و کدخدا، ا. (۱۴۰۱). پیش‌نگری خشکسالی تحت سناریوهای SSP تا پایان قرن بیست ویکم، مطالعه موردی: حوضه دریاچه ارومیه. مجله تحقیقات آب و خاک ایران، پذیرفته شده برای انتشار.
ثناگر دربانی، ا.؛ رفیعیان، م.؛ حنایی، ت. و منصفی پراپری، د. (1397). ارزیابی اثرات تغییرات اقلیمی بر تغییرات آسایش حرارتی بیرونی با استفاده از شاخص دمای معادل فیزیولوژیکی (PET) در شهر مشهد. فصلنامه تحقیقات جغرافیایی، ۳۳ (۳)، ۳۸-۵۷.
فلاح قالهری، غ.؛ اسماعیلی، ر. و شاکری، ف. (1395). ارزیابی روند تغییرات فصلی تنش‌های گرمایی طی نیم قرن اخیر در چند نمونه اقلیمی ایران. سلامت و محیط‌زیست، ۹(۲)، ۲۳۳-۲۴۶.
Abdel-Ghany, A. M., Al-Helal, I. M., & Shady, M. R. (2013). Human thermal comfort and heat stress in an outdoor urban arid environment: a case study. Advances in Meteorology, 2013.
Antonescu, B., Mărmureanu, L., Vasilescu, J., Marin, C., Andrei, S., Boldeanu, M., Ene, D., & Ţilea, A. (2021). A 41‐year bioclimatology of thermal stress in Europe. International Journal of Climatology, 41(7), 3934-3952.
Blazejczyk, K., Epstein, Y., Jendritzky, G., Staiger, H., & Tinz, B. (2012). Comparison of UTCI to selected thermal indices. International journal of biometeorology, 56(3), 515-535.
Błażejczyk, K., Jendritzky, G., Bröde, P., Fiala, D., Havenith, G., Epstein, Y., Psikuta, A., & Kampmann, B. (2013). An introduction to the universal thermal climate index (UTCI). Geographia Polonica, 86(1), 5-10.
Burton, I., Ebi, K. L., & McGregor, G. (2009). Biometeorology for adaptation to climate variability and change. In Biometeorology for Adaptation to Climate Variability and Change, (pp. 1-5). Springer, Dordrecht.
Daufresne, M., Lengfellner, K., & Sommer, U. (2009). Global warming benefits the small in aquatic ecosystems. Proceedings of the National Academy of Sciences, 106(31), 12788-12793.
Goovaerts, P. (2000). Geostatistical approaches for incorporating elevation into the spatial interpolation of rainfall. Journal of hydrology, 228(1-2), 113-129.
Hamed, K. H. (2008). Trend detection in hydrologic data: the Mann–Kendall trend test under the scaling hypothesis. Journal of hydrology, 349(3-4), 350-363.
Hamed, K. H., & Rao, A. R. (1998). A modified Mann-Kendall trend test for autocorrelated data. Journal of hydrology, 204(1-4), 182-196.
Hersbach, H., Bell, B., Berrisford, P., Hirahara, S., Horányi, A., Muñoz‐Sabater, J., Nicolas, J., Peubey, C., Radu, R., Schepers, D., & Simmons, A. (2020). The ERA5 global reanalysis. Quarterly Journal of the Royal Meteorological Society, 146(730), 1999-2049.
IPCC, (2021). Climate Change 2021: the Physical Science Basis Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (2021)
Kendall, M. G. (1948). Rank correlation methods.
Koźmiński, C., & Michalska, B. 2019, UTCI Assessment of bioclimatic conditions for recreation and tourism in the Polish Baltic coastal zone using the UTCI index. Przegląd Geograficzny.
Liu, X. M., Xu, J. M., Zhang, M. K., Huang, J. H., Shi, J. C., & Yu, X. F. (2004). Application of geostatistics and GIS technique to characterize spatial variabilities of bioavailable micronutrients in paddy soils. Environmental geology, 46(2), 189-194.
Maghrabi, A. H., & Alotaibi, R. N. (2018). Long-term variations of AOD from an AERONET station in the central Arabian Peninsula. Theoretical and Applied Climatology, 134, 1015-1026.
Mann, H. B. (1945). Nonparametric tests against trend. Econometrica: Journal of the econometric society, 245-259.
Mölders, N. (2019). Outdoor Universal Thermal Comfort Index Climatology for Alaska. Atmospheric and Climate Sciences, 9(04), 558.
Pantavou, K., Lykoudis, S., Nikolopoulou, M., & Tsiros, I. X. (2018). Thermal sensation and climate: A comparison of UTCI and PET thresholds in different climates. International journal of biometeorology, 62(9), 1695-1708.
Pantavou, K., Santamouris, M., Asimakopoulos, D., & Theoharatos, G. (2014). Empirical calibration of thermal indices in an urban outdoor Mediterranean environment. Building and environment, 80, 283-292.
Pecelj, M. M., Lukić, M. Z., Filipović, D. J., Protić, B. M., & Bogdanović, U. M. (2020). Analysis of the Universal Thermal Climate Index during heat waves in Serbia. Natural Hazards and Earth System Sciences, 20(7), 2021-2036.
Silva, T. J. V., & Hirashima, S. Q. S. (2021). Predicting urban thermal comfort from calibrated UTCI assessment scale-A case study in Belo Horizonte city, southeastern Brazil. Urban Climate, 36, 100652.
Staiger, H., Laschewski, G., & Matzarakis, A. (2019). Selection of appropriate thermal indices for applications in human biometeorological studies. Atmosphere, 10(1), 18.
Talhi, A., Barlet, A., Bruneau, D., & Aichour, B. (2020). Towards a prediction of outdoor human thermal comfort adapted for designers of urban spaces: examining UTCI and APCI in the context of Algiers (Algeria). International Journal of Biometeorology, 1-12.
Ullah, S., You, Q., Wang, G., Ullah, W., Sachindra, D.A., Yan, Y., Bhatti, A.S., Abbas, A., & Jan, M.A. (2022). Characteristics of human thermal stress in South Asia during 1981–2019: Environmental Research Letters, 17(10), 104018.
Urban, A., Di Napoli, C., Cloke, H.L., Kyselý, J., Pappenberger, F., Sera, F., Schneider, R., Vicedo-Cabrera, A.M., Acquaotta, F., Ragettli, M.S., & Íñiguez, C. (2021). Evaluation of the ERA5 reanalysis-based Universal Thermal Climate Index on mortality data in Europe. Environmental research, 198, 111227.
Vinogradova, V. (2020). Using the Universal Thermal Climate Index (UTCI) for the assessment of bioclimatic conditions in Russia. International journal of biometeorology.
Zare, S., Hasheminejad, N., Shirvan, H. E., Hemmatjo, R., Sarebanzadeh, K., & Ahmadi, S. (2018). Comparing Universal Thermal Climate Index (UTCI) with selected thermal indices/environmental parameters during 12 months of the year. Weather and climate extremes, 19, 49-57.
Zeng, D., Wu, J., Mu, Y., Deng, M., Wei, Y., & Sun, W. (2020). Spatial-temporal pattern changes of UTCI in the China-Pakistan economic corridor in recent 40 years. Atmosphere, 11(8), 858.
Zhao, Y., Ducharne, A., Sultan, B., Braconnot, P., & Vautard, R. (2015). Estimating heat stress from climate-based indicators: present-day biases and future spreads in the CMIP5 global climate model ensemble. Environmental Research Letters, 10(8), 084013.