Mapping the urban heat island

This summer, more than 120 volunteer community scientists collected data in Hennepin and Ramsey Counties as part of NOAA’s 2024 Urban Heat Island Mapping Campaign.

Using heat sensors mounted on their cars, the volunteers traversed designated routes in the morning, afternoon, and evening on one of the hottest days of the year. The sensors recorded data every second measuring temperature, humidity, time, and location.

Hennepin County will use this data to map urban heat islands and understand which parts of the county are most vulnerable to extreme heat. 

Hear from Hennepin County staff and volunteers how the study worked

What is an urban heat island?

Urban heat islands are areas that get much hotter than surrounding areas, particularly during the summer. These areas have more roads, buildings, and other surfaces that absorb and radiate heat. They also have fewer trees and greenspace that help keep areas cooler. The combination of these characteristics creates “islands” where the temperature measured can be significantly higher than the temperatures of surrounding areas. The continued rise of temperatures due to climate change and continued growth of urban areas will likely make the urban heat island effect worse.

Learn more about the urban heat island effect and impacts from study volunteers

When will the data and maps be available?

The data collected by volunteers is currently being processed and analyzed. The results should be available this fall.

How will Hennepin County use the data?

The urban heat island maps will inform our extreme heat strategy, including:

• Continuously monitoring key temperature and humidity measures at the city level
• Working closely with the National Weather Service to provide forecasting, alerts and warnings
• Developing detailed urban heat island mapping to focus efforts in the most impacted areas
• Providing education for the public, especially those most susceptible or exposed to heat
• Creating more opportunities for the public to access air-conditioned spaces
• Planting trees along streets to increase shade, especially in areas with lower tree canopy.
• Adding vegetation to urban spaces, including with green roofs and urban agriculture
• Implementing cool surfaces on roofs and walls
• Reducing paved area or using permeable or cool pavements

Don’t we already know where urban heat islands are?

The Metropolitan Council has urban heat island maps from 2016 and 2022. These maps show land surface temperatures measured by satellites, which can be the temperature of the ground, the tops of buildings, or the tree canopy.

This urban heat island study conducted this summer measured air temperature and humidity, which can be different than land surface temperature and is more relevant to the impact of heat on human health.

Comparing the patterns between the Metropolitan Council maps and the map from the urban heat study will deepen our understanding of extreme heat in the region.

Additionally, the county is exploring ways to continue to update and monitor temperatures going forward as our climate and built environment change.

Additional information and resources

News coverage

• Minnesota drivers help map out the hottest neighborhoods across the United States from KSTP Eyewitness News
• Researchers zero in on areas hardest hit by heat island effect from the Sahan Journal
• In the Twin Cities, mapping the warming urban heat island to prepare for an even hotter future from MPR News

Resources

• Urban heat islands flyer (PDF)
• Staying cool in the summer while saving energy
• Cooling options in Hennepin County
• Improving home energy efficiency (Minnesota Department of Commerce)
• Weatherization assistance program (Minnesota Department of Commerce)