The Confluence Projects
We measure extreme environmental events where people live and link them to health records at scale.
The Confluence Projects bring environmental data science together with clinical informatics and biostatistics at Massachusetts General Hospital, Harvard Medical School, and the Harvard T.H. Chan School of Public Health. Our core resource, GridEX, delineates extreme heat and cold events on a 500 m grid across the contiguous United States from 2008 to 2022.
What we study
Exposure where people live
Studies of extreme heat and cold have long assigned each person the reading from the nearest weather station, which misclassifies who was exposed during an event. GridEX estimates daily apparent temperature, which accounts for humidity and wind, and traces the boundary of each extreme event as it moves. Because the output is gridded, it links to health data at any geographic scale.
Extreme events in community health centers
Through the Community CATALYST Center, we link GridEX to the shared electronic health record of OCHIN, a national network of community health centers. The first study from this linkage analyzed 4.2 million ambulatory encounters at 2,554 centers in 40 states and appeared in JAMA Network Open in September 2026.
Extreme events and aging
Older adults carry a disproportionate share of the health burden from extreme heat and cold. With support from the National Institute on Aging, we use GridEX to study how these events relate to health and health care use in later life. In the community health center study, blood pressure fell further on extreme heat days in adults 65 and older than in younger adults.
GridEX is open data
GridEX catalogs extreme heat and cold events for the contiguous United States, with daily surfaces of temperature, dew point, wind speed, and apparent temperature. Raster layers come as GeoTIFF and event boundaries as GeoPackage, released under the MIT license. The method is described in Environmental Science & Technology (2025).
Latest
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Asking GridEX: a roadmap for AI-assisted querying and decision-making
How we plan to let investigators, clinics, and public health agencies ask GridEX compound questions in plain language and plan around the answers.
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Extreme heat and blood pressure in community health centers, in JAMA Network Open
The first study to link GridEX to the OCHIN network analyzed 4.2 million ambulatory encounters at 2,554 community health centers in 40 states.
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GridEX published in Environmental Science & Technology
The method and data pipeline behind GridEX, our 500 m national catalog of extreme heat and cold events, is now peer reviewed and open access.
Support and partners
Funded by the National Institute on Aging (RF1AG074372, continued as R01AG074372) and the National Institute on Minority Health and Health Disparities (P20MD019799).
