Science Policy
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Improve Extreme Heat Monitoring by Launching Cross-Agency Temperature Network

04.01.24 | 7 min read | Text by Bianca Corpuz

Year after year, record-breaking air temperatures and heat waves are reported nationwide. In 2023, Death Valley, California experienced temperatures as high as 129°F — the highest recorded temperature on Earth for the month of June—and in July,  Southwest states experienced prolonged heat waves where temperatures did not drop below 90°F. This is especially worrisome as the frequency, intensity, and duration of rising temperatures are projected to increase, and the leading weather-related cause of death in the United States is heat. To address this growing threat, the Environmental Protection Agency (EPA) and the National Oceanic and Atmospheric Administration (NOAA) should combine and leverage their existing resources to develop extreme-heat monitoring networks that can capture spatiotemporal trends of heat and protect communities from heat-related hazards. 

Urban areas are particularly vulnerable to the effects of extreme heat due to the urban heat island (UHI) effect. However, UHIs are not uniform throughout a city, with some neighborhoods experiencing higher air temperatures than others. Further, communities with higher populations of Color and lower socioeconomic status disproportionately experience higher temperatures and are reported to have the highest increase in heat-related mortality. It is imperative for local government officials and city planners to understand who is most vulnerable to the impacts of extreme heat and how temperatures vary throughout a city to develop effective heat mitigation and response strategies. While the NOAA’s National Weather Service (NWS) stations provide hourly, standardized air measurements, their data do not capture intraurban variability.

Challenge and Opportunity

Heat has killed more than 11,000 Americans since 1979, yet an extreme heat monitoring network does not exist in the country. While NOAA NWS stations capture air temperatures at a central location within a city, they do not reveal how temperatures within a city vary. This missing information is necessary to create targeted, location-specific heat mitigation and response efforts.

Synergistic Environmental Hazards and Health Impacts

UHIs are metropolitan areas that experience higher temperatures than surrounding rural regions. The temperature differences can be attributed to many factors, including high impervious surface coverage, lack of vegetation and tree canopy, tall buildings, air pollution, and anthropogenic heat. UHIs are of significant concern as they contribute to higher daytime temperatures and reduce nighttime cooling, which in turn exacerbates heat-related deaths and illnesses in densely populated areas. Heat-related illnesses include heat exhaustion, cramps, edema, syncope, and stroke, among others. However, heat is not uniform throughout a city, and some neighborhoods experience warmer temperatures than others in part due to structural inequalities. Further, it has been found that, on average, People of Color and those living below the poverty line are disproportionately exposed to higher air temperatures and experience the highest increase in heat-related mortality. As temperatures continue to rise, it becomes more imperative for the federal government to protect vulnerable populations and communities from the impacts of extreme heat. This requires tools that can help guide heat mitigation strategies, such as the proposed interagency monitoring network. 

High air temperatures and extreme heat are also associated with poor air quality. As common pavement surfacing materials, like asphalt and concrete, absorb heat and energy from the sun during the day, the warm air at the surface rises with present air pollutants. High air temperatures and sunlight are also known to help catalyze the production of air pollutants such as ozone in the atmosphere and impact the movement of air and, therefore, the movement of air pollution. As a result, during extreme heat events, individuals are exposed to increased levels of harmful pollutants. Because poor air quality and extreme heat are directly related, the EPA should expand its air quality networks, which currently only detect pollutants and their sources, to include air temperature. Projections have determined extreme heat events and poor air quality days will increase due to climate change, with compounding detriments to human health

Furthermore, extreme heat is linked not only to poor air quality but also to wildfire smoke—and they are becoming increasingly concomitant. Projections report with very high confidence that warmer temperatures will lengthen the wildfire season and thus increase areas burned. Similar to extreme heat’s relationship with poor air quality, extreme heat and wildfire smoke have a synergistic effect in negatively impacting human health. Extreme heat and wildfire smoke can lead to cardiovascular and respiratory complications as well as dehydration and death. These climatic hazards have an even larger impact on environmental and human health when they occur together.

As the UHI effect is localized and its causes are well understood, urban cities are ideal locations to implement heat mitigation and adaptation strategies. To execute these plans equitably, it is critical to identify areas and communities that are most vulnerable and impacted by extreme heat events through an extreme heat monitoring network. The information collected from this network will also be valuable when planning strategies targeting poor air quality and wildfire smoke. The launch of an extreme heat monitoring network will have a considerable impact on protecting lives. 

Urban Heat Mapping Efforts

Both NOAA and EPA have existing programs that aim to map, reduce, or monitor UHIs throughout the country. These efforts may have the capacity to also implement the proposed heat monitoring network. 

Since 2017, NOAA has worked with the National Integrated Heat Health Information System (NIHHIS) and CAPA Strategies LLC to fund yearly UHI mapping campaign programs, which has been instrumental in highlighting the uneven distribution of heat throughout U.S. cities. These programs rely on community science volunteers who attach NOAA-funded sensors to their cars to collect air temperature, humidity, and time data. These campaigns, however, are currently only run during summer months, and not all major cities are mapped each year. NOAA’s NIHHIS has also created a Heat Vulnerability Mapping Tool, which impressively illustrates the relationship between social vulnerability and heat exposure. These maps, however, are not updated in real-time and do not display air temperature data. Another critical tool in mapping UHIs is NWS recently created HeatRisk prototype, which identifies risks of heat-related impacts in numerous parts of the country. This prototype also forecasts levels of heat concerns up to seven days into the future. However, HeatRisk does not yet provide forecasts for the entire country and uses NWS air temperature products, which do not capture intraurban variability. The EPA has a Heat Island Reduction program dedicated to working with community groups and local officials to find opportunities to mitigate UHIs and adopt projects to build heat-resilient communities. While this program aims to reduce and monitor UHIs, there are no explicit monitoring or mapping strategies in place. 

While the products and services of each agency have been instrumental in mapping UHIs throughout the country and in heat communication and mitigation efforts, consistent and real-time monitoring is required to execute extreme heat response plans in a timely fashion. Merging the resources of both agencies would provide the necessary foundation to design and implement a nationwide extreme heat monitoring network.

Plan of Action

Heat mitigation strategies are often city-wide. However, there are significant differences in heat exposure between neighborhoods. To create effective heat adaptation and mitigation strategies, it is critical to understand how and where temperatures vary throughout a city. Achieving this requires a cross-agency extreme heat monitoring network between federal agencies. 

The EPA and NOAA should sign a memorandum of agreement to improve air temperature monitoring nationwide. Following this, agencies should collaborate to create an extreme heat monitoring network that can capture the intraurban variability of air temperatures in major cities throughout the country.

Implementation and continued success require a number of actions from the EPA and NOAA. 

  1. EPA should expand its Heat Island Reduction program to include monitoring urban heat. The Inflation Reduction Act (IRA) provided the agency with $41.5 billion to fund new and existing programs, with $11 billion going toward clean air efforts. Currently, their noncompetitive and competitive air grants do not address extreme heat efforts. These funds could be used to place air temperature sensors in each census tract within cities to map real-time air temperatures with high spatial resolution.
  2. EPA should include air temperature monitoring in their monitoring deployments. Due to air quality tracking efforts mandated by the Clean Air Act, there are existing EPA air quality monitoring sites in cities throughout the country. Heat monitoring efforts could be tested by placing temperature sensors in the same locations.
  3. EPA and NOAA should help determine vulnerable communities most impacted by extreme heat. Utilizing EPA’s Environmental Justice Screening and Mapping (EJScreen) Tool and NIHHIS’s Heat Vulnerability Mapping Tool, EPA and NOAA could determine where to place air temperature monitors, as the largest burden due to extreme heat tends to occur in neighborhoods with the lowest economic status.
  4. NOAA should develop additional air temperature sensors. NOAA’s summer UHI campaign programs highlight the agency’s ability to create sensors that capture temperature data. Given their expertise in capturing meteorological conditions, NOAA should develop national air temperature sensors that can withstand various weather conditions.
  5. NOAA should build data infrastructure capable of supporting real-time monitoring. Through NIHHIS, the data obtained from the monitoring network could be updated in real-time and be publicly available. This data could also merge with the current vulnerability mapping tool and HeatRisk to examine extreme heat impacts at finer spatial scales. 

Successful implementation of these recommendations would result in a wealth of air temperature data, making it possible to monitor extreme heat at the neighborhood level in cities throughout the United States. These data can serve as a foundation for developing extreme heat forecasting models, which would enable governing bodies to develop and execute response plans in a timely fashion. In addition, the publicly available data from these monitoring networks will allow local, state, and tribal officials, as well as academic and non-academic researchers, to better understand the disproportionate impacts of extreme heat. This insight can support the development of targeted, location-specific mitigation and response efforts.


As temperatures continue to rise in the United States, so do the risks of heat-related hazards, morbidity, and mortality. This is especially true for urban cities, where the effects of extreme heat are most prevalent. A cross-agency extreme-heat monitoring network can support the development of equitable heat mitigation and disaster preparedness efforts in major cities throughout the country.

This idea of merit originated from our Extreme Heat Ideas Challenge. Scientific and technical experts across disciplines worked with FAS to develop potential solutions in various realms: infrastructure and the built environment, workforce safety and development, public health, food security and resilience, emergency planning and response, and data indices. Review ideas to combat extreme heat here.

Frequently Asked Questions
How are urban heat islands formed?
Cities often have less vegetation and tree canopy cover than surrounding rural areas, which decreases cooling and evaporation. Tall buildings and ones that are close together reduce wind speed, trapping heat within a city. Buildings, as well as roads, streets, and sidewalks, are very good at absorbing and storing heat from the sun. Additionally, air pollution and heat from cars, buildings, and space heating absorb heat that is trying to escape from the city.
What is the difference between urban heat islands and heat waves?

Urban heat islands are urbanized regions experiencing higher temperatures compared to nearby rural areas. Heat waves—also known as extreme heat events—are persistent periods of unusually hot weather lasting more than two days. Research has found, however, that urban heat islands and heat waves have a synergistic relationship.

How many people die due to heat in the United States?

Nationwide, more than 1,300 annual deaths are estimated to be attributable to extreme heat. This number is likely an undercount, as medical records do not regularly include the impact of heat when describing the cause of death.

What can communities do to combat rising temperatures?
Cities can create more green spaces and plant more trees to increase evapotranspiration rates and provide shade. Installing cool or green roofs can reduce the amount of heat buildings store throughout the day. Altering roads, streets, or sidewalks with cool pavements may also reduce the amount of stored heat and provide less heat stress to pedestrians. Walking and biking instead of using an automobile, when possible, would reduce the amount of pollution introduced into the air, which could not only combat rising temperatures but also improve air quality.