Project Summary In the United States health impacts related to heat exposure are changing rapidly and the burdens are markedly inequitable. While we have a strong understanding of the hazard, vulnerability, and population factors driving heat-health risks, and we have information on effective risk reduction interventions, translating these insights into intervention implementation has been challenging. To address this need and support adaptation at scale, we have developed Climate and Health Risk Tool (CHaRT), an innovative decision support platform that supports heat governance processes at the local level. CHaRT provides clear, consistent, transparent risk assessment at the census tract level and links risk assessment with evidence-based intervention guidance, allowing for community-engaged adaptation planning. CHaRT has been piloted but not formally evaluated. The Research Project has two aims: to evaluate the effectiveness of facilitated engagement with CHaRT, and to assess barriers and facilitators to CHaRT implementation. To achieve the first aim, we will measure the intervention’s effectiveness through a pilot randomized controlled trial comparing facilitated CHaRT engagement with an information-only control. We will recruit 30 local health departments to participate in the trial with the help of the National Association of City and County Health Officials (NACCHO), the national member organization for local health departments, CDC and Public Health-Seattle & King County, a local health department that has used CHaRT in a pilot engagement. We will conduct pre-intervention assessments to capture each organization’s demographics and heat-health activities and describe the breadth and effectiveness of pre-intervention activities using the RE AIM framework to describe activity Reach, Effectiveness, Adoption, Implementation, and Maintenance. One year after intervention delivery, we will again assess heat-health activities and assess differences in the intervention and control groups. To achieve the second aim, we will conduct a series of key informant interviews with the intervention group to identify barriers and facilitators of CHaRT implementation and analyze the data using the Consolidated Framework for Intervention Research (CFIR). Our team is well positioned to do this work based on our prior experience with heat-health vulnerability and adaptation assessment, implementation of heat-health risk reduction interventions, and experience with program evaluation and implementation science. The work includes several innovations, including evaluation of a novel decision support tool, new methods to assess intervention effectiveness, and the use of implementation science to gain insight into climate adaptation activities. The work will result in several products and insights and lay the foundation for future work including an expanded randomized trial.