Quantifying the impact of changing the threshold of New York City heat emergency plan in reducing heat-related illnesses

The adverse health impact of high heat is widely documented and can lead to a substantial public health burden. Although heat-related illness in western countries is largely preventable, extreme heat remains the main weather contributor to the burden of disease in the United States. In most US cities, local National Weather Service offices issue heat alerts in advance of forecast periods of high heat. In some locations, additional local heat emergency plans that include additional community-based actions to protect the public from the health impacts of heat are also triggered. In 2008, the NYC Health Department made changes in their local heat emergency plan by lowering the threshold for triggering heat advisories based on evidence from local epidemiological studies. This study aims to quantify the potential benefits associated with the change in the threshold the NYC Heat Emergency Plan in reducing heat-related illnesses for Medicare fee-for service beneficiaries aged 65 years or older. We apply a quasi-experimental study design using the Difference-in-Differences (DID) method coupled with the propensity-score matching and compare the difference in daily rates of heat-related illnesses between eligible and non-eligible days before and after implementing the threshold change (2006?2007 versus 2009?2010). We reveal that the change in threshold for the NYC Heat Emergency Plan is associated with reduced daily number of 0.80 (95%CI: 0.27; 1.33) Heat-related Illnesses during hot days as compared to a counterfactual scenario in which the original threshold did not change. This highlights the benefits of local epidemiological evidence in informing emergency heat action plans, in decreasing the health burden of high ambient heat.