FAIRFAX, ARLINGTON, & ALEXANDRIA, VA: On “Measurement Day” — July 16, 2026 — more than 30 teams of citizen scientists will measure temperature and humidity variations along 30 routes in Fairfax and Arlington counties, and Alexandria as part of the “Urban Heat Island Mapping Project.”
Extreme heat is the leading cause of weather-related mortality in the United States. In an urban environment, temperatures can vary drastically between adjacent neighborhoods due to dark, heat-absorbing surfaces and a lack of tree canopy.
“This will be the most granular measurement of heat ever attempted throughout Northern Virginia,” said Chris Topoleski, executive director of Faith Alliance for Climate Solutions (FACS). “We know that neighborhoods with few trees and a lot of asphalt can be dangerously hot in summer. Once we’re done, we’ll know how hot these neighborhoods are.”
The Urban Heat Island Mapping Project is a collaboration between FACS and George Mason University’s Virginia Climate Center. The Climate Center forecasts Thursday, July 16, will be one of the hottest days of the year.
“Heat risk is on the rise and Virginians are already feeling the impacts,” said James Kinter, director of GMU’s Virginia Climate Center and Center for Ocean Land Atmosphere Studies. “High temperatures and humidity can lead to heat stress, heat stroke, and even death.”
Each volunteer team will consist of at least two people in a vehicle with a rooftop sensor. A special phone app will transmit data to GMU. Measurements will be taken along routes previously selected by the Virginia Climate Center at three times throughout the day: Morning (6–8 AM), Afternoon (2–4 PM), and Evening (6–8 PM).
The Climate Center will later render the data into high-resolution heat maps that will indicate which neighborhoods need intervention to reduce dangerous summer temperatures.
In phase two, the completed research will be shared by FACS with local elected officials and staff to inform policy decisions such as tree canopy expansion and other initiatives.
The American Red Cross-National Capital Chapter is supporting the Project by offering its regional headquarters in Fairfax County as a staging site.
About FACS: Faith Alliance for Climate Solutions is a nonpartisan nonprofit incorporated in 2016 that organizes the power of Virginia’s faith communities and people of goodwill to advance local solutions to the urgent moral challenge of climate change. Learn more.