Heat–Health Warning Systems: A Comparison of the Predictive Capacity of Different Approaches to Identifying Dangerously Hot Days

摘要

Objectives. We compared the ability of several heat–health warning systems to predict days of heat-associated mortality using common data sets. Methods. Heat–health warning systems initiate emergency public health interventions once forecasts have identified weather conditions to breach predetermined trigger levels. We examined 4 commonly used trigger-setting approaches: (1) synoptic classification, (2) epidemiologic assessment of the temperature–mortality relationship, (3) temperature–humidity index, and (4) physiologic classification. We applied each approach in Chicago, Illinois; London, United Kingdom; Madrid, Spain; and Montreal, Canada, to identify days expected to be associated with the highest heat-related mortality. Results. We found little agreement across the approaches in which days were identified as most dangerous. In general, days identified by temperature–mortality assessment were associated with the highest excess mortality. Conclusions. Triggering of alert days and ultimately the initiation of emergency responses by a heat–health warning system varies significantly across approaches adopted to establish triggers. Prompted by growing concerns about global warming and past dramatic heat wave events, 1 – 3 many jurisdictions worldwide have introduced partnerships between weather services, civil protection agencies, and public health authorities to inform their residents about and protect them from the dangers of hot weather to health. 4 – 9 Major components of these heat plans are announcing advisories and implementing emergency measures when forecast weather is expected to adversely affect the health of all or selected residents of a city or region. Collectively, such initiatives are called heat–health warning systems (HHWSs). HHWSs are designed to be activated, or triggered, once temperature and possibly other weather factors are forecast to breach predefined values expected to be associated with unacceptable levels of adverse health effects. These values are commonly referred to as triggers, and the optimal setting of triggers facilitates efficient and coordinated emergency responses; effective communication among civil protection, meteorological, and public health authorities; and, of course, reduction of heat-related mortality and morbidity. Fundamentally different trigger-setting procedures are used by various HHWSs in cities, regions, and countries across North America and Europe, and in some parts of Australia and Asia. 10 – 13 Such variations reflect different theories about the nature of the relationship between heat and health. For example, triggers may be determined by epidemiological analysis of retrospective mortality data 12 or from experimental models of heat stress and known physiologic effects of heat fluxes. 14 Variations between the approaches may also reflect differences in specific objectives and proprietorship. More prosaic reasons may also account for differences: after the 2003 heat wave in Paris, France, French researchers were given limited time and resources to devise a system and from necessity employed a relatively simple approach. 12 Despite these differences, the general goal of each system should, in principle, be the same: to identify those days associated with the largest health effects attributable to adverse weather conditions. To date, however, no study has examined the extent to which identification (and eventual triggering) of heat-alert days depends on the particular approach used to establish triggers. We compared alternative approaches for setting HHWS triggers by measuring how well they predicted heat-associated mortality from a common set of historical weather and mortality records. Our primary objective was to assess the degree to which the same heat-alert days were identified by the different approaches.