The incorporation of seasonal and temporal variability in mortality response to hot weather into operational heat watch warning systems (HWWS)

Results of temporal and seasonal heat-related mortality show significant variability across the US. While heat-related mortality on the hottest summer days has declined since the 1970s, the rate of heat-related mortality is still statistically significant in many cities, and mean anomalous mortality on oppressive days has remained relatively constant since the mid-1990s. Over the course of the year, mean mortality response is greatest in early- to mid-summer across most of the larger northeastern and Midwestern cities, but is shifted into the spring in southern cities.

The analysis of the relationship between heat and health has significant implications for heat watch warning systems (HWWS). While single thresholds of a variable, e.g. heat index, can be used successfully in HWWS, more precise associations between heat and excess death can be had by using a relative index. The Spatial Synoptic Classification (SSC) is one such metric; the weather types that go into the SSC modify in character over the course of the season cycle, making it easier to identify days that are oppressive relative to the time of year, not to an absolute threshold. In this presentation, an overview is presented describing how variability in the mortality response across season is incorporated into the more than 30 HWWS currently running across the US and around the world.