Extreme heat is the deadliest of all weather-related hazards, yet also the most preventable. To boost heat preparedness and response, officials need information on where heat-related health issues concentrate and how risks vary by demographic, social, environmental, and infrastructural factors. We present a tool for heat-health vulnerability assessments, called ClimaWATCH, which links large, diverse data to summarize county, state, and national exposure to heatwaves; susceptibility based on various factors; and heat-related health burdens.

Leveraging a case-crossover study design to calculate excess healthcare utilization and spending attributable to heatwaves, the tool clarifies how heat-related health effects vary by year, diagnosis, subpopulation, and care setting, and the financial burden of heat-related health impacts. Nationally in 2020, excess Medicaid spending amounted to $18 million on heat stress, $15 million on electrolyte imbalance, $25 million on acute myocardial infarction, and $133 million on acute renal failure. Per-beneficiary levels of excess spending on these four acute diagnoses were highest in Massachusetts, Pennsylvania, and California.

The dynamic functionality facilitates exploration of heterogeneity in effects, which can improve emergency preparedness, since heat-related health burdens can vary substantially from year to year or by demographic and community features, heatwave definition, or geographic region.

Chief heat officers, public health officials, philanthropic organizations, and others can use ClimaWATCH to develop data-driven, tailored heat action plans to address the needs of different vulnerable populations effectively and equitably, prioritize interventions based on their potential for impact, and improve community and health system resilience to extreme heat.