Abstract
The increasing frequency, intensity and duration of heat waves seem to follow the observed global warming in recent decades. Vulnerability to heat waves is expected to increase in urban environments mainly due to population density and the effect of the urban heat island that make cities hotter than surrounding non-urban areas. The present study focuses on a vulnerable area of the eastern Mediterranean, already characterized as a ‘hot spot’ with respect to heat-related risk and investigates the change in heat stress levels during heat wave compared to non-heat wave conditions as well as the way that heat stress levels respond to heat waves in urban, compared to non-urban, environments. The adoption of a metric accounting for both the intensity and duration of the hot event yielded a total of 46 heat wave episodes over a nearly 60-year period, but with very rare occurrence until the late 1990s and a profound increased frequency thereafter. The results reveal a difference of at least one thermal stress category between heat wave and non-heat wave periods, which is apparent across the entire range of the thermal stress distribution. The analysis demonstrates a robust intensification of nighttime heat stress conditions in urban, compared to non-urban, sites during severe heat waves. Nevertheless, severe heat waves almost equalize heat stress conditions between urban and non-urban sites during midday.
Highlights
Heat waves have only lately been acknowledged as a major threat to environment and society [1], they are related to more deaths than other extreme events [2]
The results reveal that the frequency of cases with HD ≥ 40, which indicates at least ‘great discomfort—avoid exertion’ (Table 1), rose up to 23.0% during heat waves waves (HWs) compared to the frequency of 1.4% which corresponded to non-HW conditions
Specific characteristics of HWs such as intensity, duration or seasonal timing combined with population vulnerability have been found to control devastating impacts on human health [2]
Summary
Heat waves (hereafter HWs) have only lately been acknowledged as a major threat to environment and society [1], they are related to more deaths than other extreme events [2]. The increasing frequency, intensity and duration of HWs in different world regions seem to follow the observed global warming in recent decades [3,4]. The populations in low and middle income countries are more affected from HWs as compared to high income countries and as global warming progresses, they will still be more affected [13]. There is no standard and universal definition for HWs. Several metric systems (indices) and approaches have been proposed in order to detect and investigate these abnormal heat events based on either absolute or relative (percentile) thresholds
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