Intensification of thermal risk in Mediterranean climates: evidence from the comparison of rational and simple indices

  • George KatavoutasEmail author
  • Dimitra Founda
Original Paper


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 


Funding information

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).

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© ISB 2019

Authors and Affiliations

  1. 1.National Observatory of AthensInstitute for Environmental Research and Sustainable DevelopmentAthensGreece

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