Extreme Heat Adaptation

Though heat affects everyone, not everyone is impacted equally. Factors influencing vulnerability to heat include where a person lives or works, access to housing, occupation, income, age, degree of social isolation, and prevalence of preexisting medical conditions. Spatial analysis of King County shows that local heat islands tend to have a higher proportion of people living with low incomes, seniors living alone, people with limited English proficiency, and cardiovascular disease. These hotter areas also have fewer trees and more paved surface relative to cooler areas of the county, increasing exposure for people who are most at risk. For additional SCAP actions related to urban forest canopy, see the Forest Resilience and Urban Tree Canopy Focus Area.

What's at stake

All climate projections show a continuing trend of rising summer temperatures, underscoring the need to be better prepared for extreme heat events as they exist today and with climate change. Average summer maximum temperatures in King County are projected to be about 3.7°F warmer by the 2030s and 10.5°F warmer by the 2080s compared to the 1980–2009 historical average.²¹ Nighttime temperatures also increase, limiting the potential for homes to cool and people to recover after hot days. Additionally, the likelihood of more frequent and hotter daytime heat waves increases.

Increasing temperatures and an aging population will add to heat-related health risk in western Washington. Local studies show that hospital admissions, emergency medical service calls, and risk of death in King County increase on hotter days (defined as 97°F with humidity).^{22, 23} By 2050, heat-attributable deaths in the Puget Sound lowlands (which includes western King County) under both a low and high greenhouse gas emissions scenario could increase 87- 178 percent.²⁴ Adults over age 60—a growing demographic—are particularly at risk. The number of King County residents over age 65 is projected to double from approximately 305,000 in 2020 to 617,000 in 2050, increasing from 13.4 to 21.4 percent of the projected population.²⁵

A better outcome

King County envisions a future where the harmful effects of extreme heat on people and places are equitably reduced. This will be achieved by effectively preparing for and responding to heat events, expanding the use of built and nature-based solutions that reduce extreme heat impacts, and strengthening the resilience of communities most affected. King County communities will be safe and healthy both indoors and outdoors during extreme heat events through increased access to cooling for vulnerable residents, heat-resilient infrastructure and community design, accessible and equitably distributed green spaces, increased heat safety awareness, and support for community-led heat preparedness efforts.

What we've done to get here

• Mapped areas in King County with elevated surface temperatures (known as “heat islands”) (2020). Mapping results have been used to support decisions related to placement of King County Metro bus shelter installations and property acquisitions in urban areas by the King County Land Conservation Initiative.
• Created the  King County Extreme Heat Mitigation Strategy (2024) in partnership with local governments, community partners, and frontline communities.
• Updated operational plans and increased technical capacity for heat response by King County agencies.
• Developed multilingual heat education and communications to share with community partners.

Other SCAP Actions Benefiting Heat Resilience

In addition to the actions in this Focus Area, many actions in the Climate Preparedness section and other sections of the 2025 SCAP will help to reduce the impacts of extreme heat on people and places in King County. For example, community resilience during extreme heat events will be strengthened by actions to:

• Co-develop multilingual and culturally competent heat safety and preparedness trainings (SRFC 18: Co-create community climate hazards and resilience training),
• Increase access to energy affordability programs for income-qualified residents (SRFC 35: Establish a “one stop shop” for utilities affordability programs),
• Expand heat pump installation programs to include more facility types and geographic areas (GHG 29: Directly facilitate retrofits of housing and community assets of frontline communities to reduce emissions and provide access to cooling),
• Develop building codes and policies that help to reduce heat impacts (GHG 33: Develop regional green building codes), and Support heat safety programs in schools (SRFC 8: Advance climate resilience in K–12 schools).

The 2025 SCAP also supports nature-based solutions that can cool or prevent heat islands and help residents stay cool. This includes actions that will:

• Accelerate the rate of protection of forests, parks, and natural lands (GHG 53: Protect remaining high conservation value lands),
• Increase access to green space by creating multi-benefit stormwater parks (Prep 15: Advance stormwater parks through a countywide roadmap), and
• Bolster healthy urban tree canopy coverage (Prep 29: Expand urban tree canopy and partnerships across jurisdictions). These actions collectively work together to reduce heat risk and adapt our built environment to better handle heat.

^{21  Raymond & Rogers, “Climate Mapping for a Resilient Washington,” Climate Impacts Group, University of Washington, Seattle, and Research Data & Computing Services, University of Idaho, Moscow, 2022.}

^{22  Isaksen et al, “Increased Hospital Admissions Associated with Extreme-Heat Exposure in King County, Washington, 1990–2010,” Reviews on Environmental Health, 30(1), 51–64, 2015.}

^{23  Isaksen et al, “Increased Mortality Associated with Extreme-Heat Exposure in King County, Washington, 1980–2010,” International Journal of Biometeorology, 60(1), 85–98, 2016.}

^{24  Arnold et al, “Mortality Associated with Extreme Heat in Washington State: The Historical and Projected Public Health Burden,” Atmosphere, 13(9), 1392, 2022.}

^{25  Washington Office of Financial Management, “Growth Management Act Population Projections for Counties: 2020 to 2050,” 2023.}