Progress in Heat Watch–Warning System Technology

TLDR

Heat is the deadliest atmospheric hazard, and recent events such as the 1995 Chicago Heat Wave have driven efforts to improve oppressive‑day detection and mitigation planning. This article presents the techniques used to develop new synoptic‑based heat watch–warning systems. Unlike threshold‑based systems, the new systems identify weather conditions most strongly linked to historical mortality, account for spatial variability in mortality–weather relationships, and employ web‑based data transfer and page creation for dissemination. These systems are operational in more than two dozen global locations, providing mortality forecasts and heat‑warning recommendations to meteorological forecasters, health officials, and civic authorities.

Abstract

Among all atmospheric hazards, heat is the most deadly. With such recent notable heat events as the Chicago Heat Wave of 1995, much effort has gone into redeveloping both the methods by which it is determined whether a day will be “oppressive,” as well as the mitigation plans that are implemented when an oppressive day is forecast to occur. This article describes the techniques that have been implemented in the development of new synoptic-based heat watch–warning systems. These systems are presently running for over two dozen locations worldwide, including Chicago, Illinois; Toronto, Ontario, Canada; Rome, Italy; and Shanghai, China; with plans for continued expansion. Compared to traditional systems based on arbitrary thresholds of one or two meteorological variables, these new systems account for the local human response by focusing upon the identification of the weather conditions most strongly associated with historical increases in mortality. These systems must be constructed based on the premise that weather conditions associated with increased mortality show considerable variability on a spatial scale. In locales with consistently hot summers, weather/mortality relationships are weaker, and it is only the few hottest days each year that are associated with a response. In more temperate climates, relationships are stronger, and a greater percentage of days can be associated with an increase in mortality. Considering the ease of data transfer via the World-Wide Web, the development of these systems includes Internet file transfers and Web page creation as components. Forecasts of mortality and recommendations to call excessive-heat warnings are available to local meteorological forecasters, local health officials, and other civic authorities, who ultimately determine when warnings are called and when intervention plans are instituted.