Increased Temperature and Heat Stress

The probability of greater heat wave frequency and duration due to climate change has focused attention on the corresponding increase in heat-related mortality. Muthers et al. (2010) studied the potential development of heat-related mortality in Vienna in the 21st century using two regional climate models. The human biometeorological index PET (Physiologically Equivalent Temperature) was used to describe heat stress by incorporating both meteorological components of the thermal environment and physiological components of the human body. The relation between heat stress and mortality from 1970 to 2007 was studied in order to estimate the possible increases in mortality with and without long-term adaptation. With both approaches, heat-related mortality could increase significantly until the end of the 21st century. Carolyn Campbell
Muthers, S., Matzarakis, A., Koch, E., 2010. Climate change and mortality in Vienna—A human biometeorological analysis based on regional climate modeling. International Journal of Environmental Research and Public Health 7, 2965–2977

In order to analyze the impact of climate change on heat-related mortality, Muthers et al. first assessed the relationship between climate and mortality between 1970 and 2007. Mortality data from the National Statistical Service of Austria showed a clear seasonal cycle, with higher values in the winter and lower values in the summer. Additionally, a long-term trend of decreasing mortality was found with approximately 80 deaths per day in the early 1970s and 50 deaths per day in the early 2000s. Next the authors calculated PET for the state of Vienna using the meteorological parameters air temperature, relative humidity, wind speed, and cloud cover. Mean mortality per temperature grade was calculated for the whole period, per decade, and per year. Additionally, differences between gender and causes of death were analyzed. The impact of climate change on heat-related mortality was studied using two regional climate models, the hydrostatic REMO model and the non-hydrostatic CLM model, based on the IPCC emissions scenarios A1B and B1. The possible range of future sensitivity was calculated with and without long-term adaptation.
From 1970 to 2007, mortality on days with PET ≥ 29 °C increased significantly. Days with low heat stress (PET < 29 °C) had a mean relative mortality of –1.8%, with moderate heat stress (PET 29–35 °C) had a mortality of 0.9%, with strong heat stress (PET 35–41 °C) had a mortality of 5.8%, and with extreme heat stress (PET ≥ 41 °C) had a mortality of 13%. No significant change in the number of days per heat stress grade compared to 1971–2000 occurred from 2011–2041. Between 2041 and 2070 heat stress increased significantly in most grades of the A1B scenario and extreme grades of the B1 scenario. From 2071 to 2100, significant increases in heat stress were found for all grades. Assuming no long-term adaption, no significant increase in heat-related mortality was found for the period 2011–2040, but increases were detected for most cases in the periods 2041–2070 and 2071–2100. When assuming long-term adaptation, mortality decreases continuously on days with moderate and strong heat stress and increases slightly with extreme stress.

            While an increase in heat-related mortality is predicted by the year 2100, no significant changes were found for 2011–2040. Therefore there is time for planning and implementation of additional adaptation measures. In order to avoid significant heat-related mortality due to moderate and strong heat stress in the future, the author felt that researchers should focus now on adaptation measures such as reducing the radiation component of the thermal environment. 

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