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

• Published in: International journal of biometeorology 2019-09, Vol.63 (9), p.1251-1264
• Main Authors: Katavoutas, George, Founda, Dimitra
• Format: Article
• Language: English
• Subjects: Animal Physiology; Biological and Medical Physics; Biometeorology; Biophysics; Cities; Climate change; Climatic indexes; Discomfort; Earth and Environmental Science; Elongation; Environment; Environmental Health; Extreme heat; Extreme high temperatures; Global warming; Heat; Heat index; Heat stress; Heat tolerance; Humidity; Mediterranean climate; Meteorology; Observatories; Original Paper; Physiology; Plant Physiology; Risk; Seasonal variations; Seasons; Statistical analysis; Temperature; Trends; Urban areas; Urban development; Urban sprawl; Weather
• ISSN: 0020-7128; 1432-1254
• DOI: 10.1007/s00484-019-01742-w

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.