Cities have been assigned as one of the most vulnerable areas with respect to heat-related risk due to global warming and rapid urban growth. The present study explores the long-term trends in thermal risk at a large urban area of the eastern Mediterranean (Athens) over a long period (1960–2017), based on hourly observations. In addition to the frequency and severity of heat stress conditions, the study further explores changes in the seasonality of heat stress. Four human thermal indices with different rationales were employed, namely the Universal Thermal Climate Index (UTCI), the Physiologically Equivalent Temperature (PET), the Heat Index (HI), and the Humidex (HD). All indices indicate a prominent increase in heat-related risk over the years. The exposure time per year under the conditions of “hot-extreme caution” (HI), “great discomfort-avoid exertion” (HD), “very strong heat stress” (UTCI), and “extreme heat stress” (PET) exhibits a statistically significant increasing trend at a rate of 0.9%/decade, 0.4%/decade, 0.3%/decade, and 0.4%/decade during 1960–2017, respectively. Even during the nighttime hours, three out of the four indices indicate that the population is exposed to significantly higher heat stress levels in the recent decades compared to the past ones. A progressive expansion of the “heat stress season” over the years was revealed, resulting to an elongation of the “hot-extreme caution” season (HI), the “great discomfort-avoid exertion” season (HD), and the “very strong heat stress” season (UTCI) by 5.6 days/decade, 11.3 days/decade, and 4.3 days/decade, respectively.
Thermal comfort Heat stress Global warming impacts Urban thermal risk Human thermal indices Mediterranean
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The authors recognize the support of this work by the project “THESPIA II – Foundations of synergistic and integrated management methodologies and tools for monitoring and forecasting of environmental issues and pressures” (MIS 5002517) which is implemented under the action “Reinforcement of the Research and Innovation Infrastructure,” funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund).
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Conflict of interest
The authors declare that they have no conflict of interest.
Founda D, Kambezidis HD, Petrakis M, Zanis P, Zerefos C (2009) A correction of the recent air-temperature record at the historical meteorological station of the National Observatory of Athens (NOA) due to instrument change. Theor Appl Climatol 97:385–389. https://doi.org/10.1007/s00704-008-0084-7CrossRefGoogle Scholar
IPCC (2014) Climate change 2014: synthesis report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, Pachauri RK, Meyer LA (eds.)]. IPCC, GenevaGoogle Scholar
Slini T, Papakostas KT (2016) 30 years air temperature data analysis in Athens and Thessaloniki, Greece. In: Grammelis P (ed) Energy, transportation and global warming. Green Energy and Technology. Springer, Cham, pp 21–33. https://doi.org/10.1007/978-3-319-30127-3_3
Theoharatos G, Pantavou K, Mavrakis A, Spanou A, Katavoutas G, Efstathiou P, Mpekas P, Asimakopoulos D (2010) Heat waves observed in 2007 in Athens, Greece: synoptic conditions, bioclimatological assessment, air quality levels and health effects. Environ Res 110:152–161. https://doi.org/10.1016/j.envres.2009.12.002CrossRefGoogle Scholar
VDI (1998) VDI 3787, Part I: environmental meteorology, methods for the human biometeorological evaluation of climate and air quality for the urban and regional planning at regional level. Part I: climate. Beuth, BerlinGoogle Scholar