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Compounded heat and fire risk for future U.S. populations

Date: July 27, 2020

Fire weather and heat are coupled, compounding risk from climate change.

A three-panel map of the United States showing the number of extreme fire days.  The first shows the most fire days in the western U.S., the second shows the most in the Southeast, and the third is split between the West and Southeast.
The number of extreme fire days during 2040-2069 according to three climate models (the ensemble general circulation model, HadGEM2-ES365, and MIROC-ESM-CHEM).
Climate change is expected to increase severe weather events, including heat waves, fire, flooding, hurricanes, and drought.  These impacts will have far-reaching implications for economic and social stability, including loss of services and security.  

Climate change will greatly increase average temperature (+3.3 to 6°C) and the number of extreme fire weather days (+3.5 to 20 days) by 2040-2069 compared to the recent past (1971–2000). Hot temperatures may compromise health and outside activities for both work and leisure, such as farming, gardening, and summer sports. Fire may cause road closures, breakdown of infrastructure networks such as electricity, water supply, and health and emergency services, disruption of livelihoods, injury, ill health, or even mortality.

Both climate change and socioeconomic factors, which drive population growth, movement, and land use change, are important determinants of these risks. Rural, low density areas are most vulnerable to wildfire because they are close to vegetated areas. Urban density classes are most vulnerable to heat, due to the urban heat island effect. This means that population movement to and growth in urban centers will help reduce exposure to wildfire, but increase exposure to heat.

Risks from fire and heat may compound each other, resulting in greater risk than the sum of individual events. For example, fire may lead to post-fire flooding and debris flow due to loss of vegetation and soil erosion, intensifying vulnerability. Climate change will increase likelihood of heavy precipitation and flooding. Extreme events often interact because they are spatially and temporally dependent, meaning risk can be underestimated.

Key Findings

  • Overall, U.S. residents will have greater exposure to fire hazard (+3.5 to 20 extreme fire weather days) and heat (+3.3 to 6°C) during 2040-2069 compared to 1971–2000.
  • Movement to urban centers will help offset exposure to fire but not heat.
  • Compound risk occurs due to interactions among hazards, leading to underestimation of risk.
  • Adaptation strategies can reduce risk.

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