Adverse Climate Events*

A Climate measure
Loading interactive model…

About

Indicator of thresholds met for the following adverse climate and weather-related event categories: extreme heat (300 or more days above 90F), moderate or greater drought (65 or more weeks), and disaster (2 or more presidential disaster declarations) over the five-year period. The 2025 Annual Data Release used data from 2019-2023 for this measure.

Adverse climate and weather-related events such as intense storms, droughts, floods and extreme heat can cause injury and death; they are also becoming more frequent.1 These events directly impact physical health and safety, cause lasting harm to mental health and well-being, and disrupt communities and health systems.2 Climate and weather-related events can displace people and cause overcrowding or unsafe living conditions. The measure of Adverse Climate Events includes three types of events over a five-year period: component measures of heat, drought, and disasters, which are defined below.

Extreme heat poses immediate health threats to sensitive populations including older adults, pregnant people, young children, people with asthma or heart disease, and people living or working outdoors.3 Drought affects health primarily through detrimental effects on water and food security, and dry air can make it harder to breathe because of increased dust and particulates in the air.4,5 Disasters, especially when they happen in succession, disrupt well-being, strain physical and mental health, displace residents from their communities, and may require substantial investment for recovery.6 Disaster declarations, or the coordination of federal resources by state and federal officials to address a disaster response that has overwhelmed local and state capacity, may result in federal aid to individuals or public entities or hazard mitigation.7

Climate events worsen inequities because communities with fewer resources are often located in places with higher climate risk, such as flood zones or urban heat islands.8,9 For example, research has found that historically redlined neighborhoods have less green space and are hotter on average due to the urban heat island effect caused by less tree canopy.10 Households with fewer resources may struggle to move to safety during a disaster and struggle to rebuild, recover or relocate after a disaster. In the U.S., people whose preferred language is not English may have trouble accessing information about shelters, food distribution, health services, evacuation procedures or financial assistance. People who face multiple forms of hardship — like poverty, racism, and underemployment — can experience layered harm from the interactions of these strains. Understanding the history of adverse events can help contextualize current patterns in the community conditions supporting health and the distribution of these conditions. Furthermore, work to address inequities can lessen the impacts of future climate-related events.

People and organizations with political influence use their power to shape society’s rules, determine how disaster declarations are made, who receives aid, and how important decisions are made about communications, processes and resources in emergency response and recovery. A presidential disaster declaration requires a state governor to request federal support and the president to respond with support.7 There may be more political will to quickly declare a disaster and provide substantial aid for areas that are seen as politically or economically important due to industries or infrastructure key to national interests. When the power to set the rules is not shared fairly, the people who decide on the rules may assume they know what’s best for everyone, creating a society that does not support equity in opportunities for health. Environmental justice requires the fair treatment and meaningful involvement of all people — regardless of where they live, their race, income, or national origin — in the development, implementation, and enforcement of environmental laws, regulations, and policies.11 Our measure of Adverse Climate Events, combined with our data on Demographics and Community Conditions, helps us understand how people wield power to write rules that contribute to lasting health disparities within the context of recent climate events. When we cultivate a society that values and respects every member, led by those most affected by historical harms, we can foster a collective responsibility that supports health for everyone.

Find strategies to address Adverse Climate Events*

Loading interactive model…

Data and methods

Data Source

Environmental Public Health Tracking (EPHT) Network; U.S. Drought Monitor (USDM); OPEN FEMA Disaster Declaration Summaries

Multiple data sources contribute to this measure. Heat data are from the Centers for Disease Control and Prevention’s (CDC) National Environmental Public Health Tracking (EPHT) Network. The EPHT Network “brings together health data and environmental data from national, state, and city sources.” Data can be queried through the EPHT Network Data Explorer. Drought data come from the U.S. Drought Monitor (USDM), which releases a weekly map showing the locations and severity of droughts. The USDM is “produced through a partnership between the National Drought Mitigation Center at the University of Nebraska-Lincoln, the United States Department of Agriculture and the National Oceanic and Atmospheric Administration.” Drought data can be downloaded from the Weeks in Drought page. Disaster data are from the Federal Emergency Management Agency (FEMA), which “collects data on multiple aspects of emergency management” and “promotes government transparency and accountability, as well as enables collaboration with community partners.” Disaster data can be downloaded from the OpenFEMA Disaster Declarations Summaries page.

Key Measure Methods

Adverse Climate Events is an indicator

Adverse Climate Events indicates the thresholds met within the five-year period for the following adverse climate and weather-related event categories: extreme heat, moderate or greater drought, and disaster declarations. Extreme heat is defined as 300 or more days of heat at 90 degrees Fahrenheit or more over the five-year period. Moderate or greater drought is defined as 65 or more weeks in which of any portion of the county experienced moderate, severe, extreme, or exceptional drought based on the U.S. Drought Monitor categories over the five-year period. Disaster declarations are defined as two or more presidential disaster declarations within the five-year period, including declarations for coastal storms, dam levee breaks, earthquakes, fires, floods, freezing, hurricanes, landslides, severe ice storms, snow, tornados, tsunamis, typhoons and volcano eruptions, and excluding COVID-19 declarations.

Qualifying events in any of the three categories adds one value to the total count. If a county experiences qualifying adverse climate event(s) within a single category, it receives a value of 1 for the composite measure, regardless of how many events above the threshold happened within that category. If a county has qualifying event(s) in two or all three categories, it receives a value of 2 or 3 respectively. Counties can view specific event counts for each category in the measure’s disaggregated data.

Caution should be used when comparing these estimates across states

Caution should be used when comparing these estimates across states. The occurrence and impact of climate events varies geographically across the country. Presidential declarations of disasters for climate related events also vary by state because it is a political process. Governors of affected states are required to submit requests for a disaster declaration to the president if there are resources needed beyond what the state and local governments can provide. Differences in available resources for climate related disaster response and decisions by governors to request a disaster declaration may lead to state differences in disaster declarations in addition to differences in the types of climate events experienced due to a state’s location.

Caution should be used when comparing these estimates across years

Caution should be used when comparing these estimates over time. Large changes in climate take place over periods longer than five years, although climate or weather-related events caused by these changes can be seen on shorter time scales. Changes in the political environment may lead to differences over time in disaster declarations. Natural fluctuations in the climate, such as El Niño and La Niña, can occur at irregular intervals over periods of several months to years and impact temperature, drought and weather patterns.

Measure limitations

Not all climate events are equal in impact; some have greater consequences on the health of communities than others. Factors that may influence the impact of climate events on a place include infrastructure, preparedness, vulnerability, resilience and green space. The U.S. is geographically diverse, and thus different types of events will be more likely or impactful in different places across the country. Events counted in this measure could have occurred anywhere in the county and may not have affected the entire county. The five-year period used in this measure is short when compared to the long-term trajectory of trends in climate events.

Standard thresholds were set to determine qualifying events for each category. Thresholds approximating two months per year of heat (i.e., 300 consecutive or any days over five years), three months per year of drought (i.e., 65 consecutive or any weeks over five years), and multiple disasters over five years are based on literature and analysis of these data. The underlying data can be accessed to see the exact number of days, weeks, and disasters for each county. The threshold of ninety degrees for extreme heat is based on CDC guidance. It is important to keep in mind not everyone experiences heat the same way; ninety degrees may be a typical summer temperature in some places, and pregnant people, people experiencing homelessness, or people with underlying health conditions may be more affected by high temperatures. Both heat and drought are measured using any non-consecutive or consecutive time periods in order to capture all instances, but consecutive days/weeks in heat/drought will have even greater impacts on the health of residents. Alaska and Hawaii do not have heat data from EPHT, and thus measure values for their counties have a maximum of 2 rather than 3. Finally, the decision to make a presidential disaster declaration is a political process, which may result in state-by-state differences in this measure (see section on comparing estimates across states for more information).

Can This Measure Be Used to Track Progress

This measure is not intended to track progress. Human-induced changes to the climate are happening on large geographical scales over long periods of time, while natural climate fluctuations impact climate in much shorter time scales. See the section above, “Caution should be used when comparing these estimates across years,” for more information about comparing over time. Tracking local initiatives to mitigate the effects of climate change — like planting trees, building parks, installing air conditioning or cooling centers, improving irrigation systems, or hardening infrastructure to withstand disasters like tornados or hurricanes — might be more useful for tracking progress.

Finding More Data

Disaggregation means breaking data down into smaller, meaningful subgroups. Disaggregated data are often broken down by characteristics of people or where they live. Disaggregated data can reveal inequalities that are otherwise hidden. These data can be disaggregated by:

  • Subcounty Area

Census tract-level data for number of extreme heat days are available from the National Environmental Tracking Program Data Explorer in the Heat & Heat Related Illness (HRI), Historical Temperature & Heat Index, Annual Number of Extreme Heat Days (Full Year) content area. GIS data files, which can be used to evaluate the occurrence of drought at any geographic level, are available for download from the U.S. Drought Monitor.

The U.S. Climate Vulnerability Index (CVI) can help communities understand their vulnerabilities to climate change and visualize historical and projected impacts of climate change. An interactive map is available, as well as a data download that contains the 184 indicators included in the CVI. Mathematica’s ClimaWATCH tool allows communities to explore how heat waves have impacted health and increased inequities. The tool focuses on Medicaid beneficiaries and includes “data on temperature and dew point; vulnerability related to demographic social, environmental, and infrastructural factors; and direct and indirect health issues caused or worsened by heat.”

References

  1. Seneviratne SI, Zhang X, Adnan M, et al. Weather and Climate Extreme Events in a Changing Climate. Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. 1513–1766.
  2. Ebi KL, Vanos J, Baldwin JW, et al. Extreme Weather and Climate Change: Population Health and Health System Implications. Annu Rev Public Health. 2021; Apr 1(42):293-315.
  3. Centers for Disease Control and Prevention. About Heat and Your Health.
  4. Craig CA, Feng S, Gilbertz S. Water crisis, drought, and climate change in the southeast United States. Land Use Policy. 2019;88.
  5. Achakulwisut P, Mickley LJ, Anenberg SC. Drought-sensitivity of fine dust in the US Southwest: Implications for air quality and public health under future climate change. Environmental Research. 2018; 13(5).
  6. Kintziger KW, Scales SE. Escaping Disaster: Understanding the Drivers and Disparities in Disaster Displacement in the United States. American Journal of Public Health 2025; 115(1):52-54.
  7. U.S. Department of Homeland Security. FEMA. A Guide to the Disaster Declaration Process and Federal Disaster Assistance.
  8. Pallathadka A, Sauer J, Chang H, et al. Urban flood risk and green infrastructure: Who is exposed to risk and who benefits from investment? A case study of three U.S. Cities. Landscape and Urban Planning. 2022;223.
  9. Grineski SE, Collins TW, Shen L. Environmental justice and the distribution of urban heat island intensity in the United States. Environmental Justice. 2016;9(6):209-216.
  10. Hoffman JS. Hotter, Wetter, Sneezier, & Wheezier. Present-day Environmental Disparity Among HOLC Neighborhoods. Urban Institute.
  11. United States Enviornmental Protection Agency. Environmental Justice.

Find strategies in What Works for Health