Modified Project Summary/Abstract Section Community health centers (CHCs) have unparalleled expertise in addressing poor health in rural / low-income U.S. communities, which have high risk of the health impacts of extreme heat and poor air quality events. As the front line of primary care for these communities, CHCs are uniquely positioned to intervene to prepare for and mitigate these health impacts in these populations. To do so effectively, CHCs must be equipped with evidence regarding interventions that are successful in their patient populations. A crucial first step is learning specifically how extreme heat and poor air quality events impact CHC patients’ health. The Research Program Core of the Community Catalyst Center will generate this critical knowledge by assessing associations between extreme heat events and poor air quality events and health outcomes in CHC populations, with a focus on hypertension and asthma as prevalent diseases managed in CHCs. The analyses will also consider the multi-level factors that may modify these associations. These analyses will use 2013-2023 data from an EHR shared by a >1,700 CHC network spanning 36 states, linked to granular heat and air quality data. Working in bidirectional collaboration with the CHC community partners in the Center’s Community Engagement Core to ensure that analyses generate evidence that meets community needs, we will test the hypotheses that: (1) Patients exposed to extreme heat / poor air quality events will have an increased incidence of elevated blood pressure, with an additive effect if exposed to both heat and poor air quality, and a larger effect among patients with hypertension pre-event; there will also be increased incidence of hypertension, kidney, and cardiovascular diseases among patients at risk for hypertension pre-event. (2) Persons with asthma who are exposed to extreme heat / poor air quality events will experience increased asthma exacerbation; there will also be an increased incidence of asthma among exposed patients. Directed by our community partners, we will build on these analyses’ results to (3) examine potential effect modifiers such as regional characteristics and patient-level contextual drivers and comorbidities, to enable identifying strategies that CHCs might enact to prepare for and mitigate extreme heat and poor air quality event-induced health impacts, which will be assessed in future effectiveness research. The analyses conducted here will provide the foundational evidence needed to develop this community-prioritized research agenda.