The Definition of Heat-Wave Within the European Project “Improving Public Health Responses to Heat” (EuroHEAT)

Abstract

ISEE-562 Objective: Many studies have documented an increase in mortality associated to high temperatures and during heat wave episodes. To date, a standardized definition of heat wave has not been formulated. Throughout the literature different temperature variables have been considered to define a heat wave, including daily mean, maximum or minimum values, and more complex measures such as composite and biometeorological indexes. One of the aims of the EuroHEAT project was to study the impact of heat on mortality during heat waves in nine European cities (Athens, Barcelona, Budapest, London, Milan, Munich, Paris, Rome, and Valencia). Maximum apparent temperature (Tappmax), an index of thermal discomfort based on air temperature and dew point temperature, was chosen as exposure variable. Materials and Methods: For the summer period (June-August) heat waves were defined as days in which Tappmax exceeds the threshold (90th percentile of Tappmax for each month) for at least 2 days and continues as long as Tappmax is higher than its median value and minimum temperature (Tmin) exceeds its threshold (90th percentile of Tmin for each month). Minimum temperatures were specifically included to account for high night time temperatures that were observed especially in the Mediterranean cities during the 2003 heat wave, which from a preliminary analysis seemed to better depict the increase in mortality during heat episodes. Furthermore, to fully characterize each heat episode the duration, intensity, and time interval between different heat waves were also included. Results: Despite a large heterogeneity, results show the strongest effect on mortality for heat waves of a long duration and high intensity (up to 3 times) in most cities, while the first heat wave of summer had the greatest impact only in few cities. Conclusions: A heat wave definition is a milestone in the investigation of heat-related mortality.