The Effectiveness of Excessive Heat Warnings in Reducing Mortality

Extreme temperatures are historically one of the leading causes of weather-related death in the USA. This is only expected to increase with climate change. Preventing the loss of life from weather hazards is a core component of the National Weather Service (NWS) mission. The primary tool that NWS has in protecting lives is its Watch, Warning, and Advisory (WWA) program. WWAs improve mortality outcomes both by directly informing the public of hazardous conditions and advising on appropriate actions to take, as well as mobilizing social capacity like emergency management and public health resources. Little is known about the effectiveness of the WWA program in terms of reducing mortality during extreme temperature events. The issuance of extreme temperature warnings by NWS meteorologists is a discrete choice which is, in part, based on a threshold related to temperature or heat index. This threshold varies geographically, and the decision also includes some discretion on the part of the meteorologist issuing the warning, however the existence of this threshold effect creates an opportunity for a natural quasi-experiment that can be estimated with a regression discontinuity design. This research uses day-by-county Multiple Cause of Death microdata from the Center for Disease Control from 2005-2021, combined with historical heat and humidity data and NWS WWA data to estimate to reduction in mortality attributable to Heat Advisories and Excessive Heat Warnings. Initial results suggest that excessive temperature advisories and warnings prevent an average of at least 52 deaths per year. Additionally, we find that the effectiveness of these products varies with both socio-economic and climate conditions.