In the summer of 2021, record-breaking extreme heat events struck communities across the world. The unprecedented U.S. Pacific Northwest and Western Canadian heat wave took communities by surprise. Records were broken across the region, from larger cities such as Portland, Seattle, and Vancouver to smaller towns like Lytton in British Columbia. Lytton hit 121°F (49.5°C), the highest temperature ever recorded in Canada, and then tragically, was destroyed when a wildfire swept through the drought and heat-stressed forest a few days later. Record-breaking heat waves also struck historically hotter climates like the U.S. Southwest, where records were broken in cities such as Los Angeles, Las Vegas, Phoenix, and Tucson.
As average global temperatures rise, heat is increasing. This includes the frequency, length, and intensity of extreme heat events, such as heat waves, and the threat of chronic heat. Heat is already the number one weather-related killer in the United States, and heat impacts are projected to increase as temperatures continue to rise. While extreme heat events are dangerous everywhere, in climates that are already hot, chronic hot temperatures are an equally dangerous threat, often leading to more heat deaths than recognized extreme heat events.
Heat also affects communities' quality of life, local economic activity, energy and water use, wildlife, vegetation and landscaping, infrastructure, and agriculture. These negative consequences disproportionately affect marginalized residents and those who face systematic inequities such as workplace safety, housing quality, energy affordability, transportation reliability, and healthcare access.
Both climate change and the urban heat island (UHI) effect, in which the form and function of the built environment make urban areas hotter than their rural and natural surroundings, are contributing to these rising heat risks. The way communities are planned, including land uses that shape the built environment, influences both the emissions of greenhouse gases that create climate change and the UHI effect. Because planning shapes heat risk, and the profession has a responsibility to foster equity and inclusion, planners will be key practitioners in helping their communities pursue approaches and strategies to achieve greater heat resiliency.
Urban heat resilience means proactively mitigating and managing urban heat across the many systems and sectors it affects. This PAS Report, Planning for Urban Heat Resilience, seeks to elevate heat as a climate risk in the urban planning profession. The report lays out the complexity of heat, outlines the role of planners in equitably addressing heat, and presents a framework for how planners can mitigate and manage heat across a variety of plans, policies, and actions.
An Increasing, Invisible, and Inequitable Climate Risk
Hotter temperatures are impacting communities of all sizes and in all regions. Increases in both chronic and acute heat risks are compounding dangers for cities in historically hotter regions and posing new threats for cities in historically more temperate and colder climates. Cities in historically colder regions are often less prepared for heat, as they have lower adoption rates of indoor cooling and less experience managing extreme heat events. In areas with higher humidity, even small temperature increases can increase the danger to human health.
While communities everywhere are getting hotter, heat risks are unevenly and inequitably distributed. This report explains why some neighborhoods are consistently hotter than others, including districts with a history of redlining or communities of mostly low-income or minority residents. Past planning decisions played a role in creating and furthering these disparities. Certain community members are also more vulnerable to heat-related illness or death; these include children and the elderly, people with chronic health conditions or lower incomes, people experiencing homelessness, and people who are institutionalized.
Communities must prepare for increasing heat and address systemic inequities in heat risk. This report makes the case that planners are well suited to take a leading role in advancing urban heat resilience in their communities through equitable distribution of efforts, recognition of historical injustices and diverse needs of their community, and procedures such as inclusive public participation.
A Framework for Urban Heat Resilience Planning
Planners seeking to increase their communities' urban heat resilience can equitably prepare for and adapt to both chronic and acute heat risk through heat mitigation and management strategies. This PAS Report lays out a framework for addressing urban heat, which requires setting clear urban heat planning goals and developing associated metrics for success; building a comprehensive "fact base" of information on heat risks; developing a diverse portfolio of heat mitigation and management strategies; managing uncertainty; coordinating across planning efforts; ensuring inclusive participation in planning processes; and effectively implementing, monitoring, and evaluating urban heat resilience efforts.
Addressing a challenge such as heat starts with understanding the issues. This report gives planners a baseline grounding in the science behind extreme heat and the various ways it can be experienced, measured, and tracked. It rounds up data sources and analytical tools for measuring heat's impacts on communities. With this foundation in place, planners can pursue heat resilience through the dual approaches of heat mitigation and heat management.
Heat mitigation strategies aim to reduce the built environment's contribution to urban heat. While many communities are pursuing urban greening strategies, such as urban forestry and green stormwater infrastructure, to mitigate heat, a broader set of heat mitigation tools are available to planners. This report discusses heat mitigation approaches in the areas of land use, urban design, urban greening, and waste heat reduction, and it offers planners guidance on integrating heat mitigation into community visioning and engagement, plans and policies, regulations and project reviews, and public investments.
Heat management strategies are those that prepare for and respond to chronic and acute heat risk. Similarly, many communities are establishing cooling centers and early warning systems to help manage extreme heat risk, but they are leaving additional tools that better address chronic heat and systematic inequities on the table, such as ensuring access to reliable energy and indoor cooling, reductions in personal heat exposure, public health measures, and emergency management planning and response. This report explains how planners can coordinate with allied professionals on these heat management strategies to ensure community members have quality housing, indoor cooling, accessible and reliable energy, and safe and dependable transportation options.
Urban heat resilience requires effective coordination between different disciplines and sectors, such as hazard mitigation planning, public health, emergency management, the energy sector, and various levels of government. Planners should develop a diverse portfolio of heat mitigation and management strategies. These heat resilience strategies should be prioritized to maximize co-benefits, minimize tradeoffs, and avoid maladaptive strategies that provide short-term relief but worsen the problem in the long run (e.g., highly inefficient air conditioners that increase electricity demand and greenhouse gas emissions). Because heat resilience strategies will likely be needed across a variety of community plans, the report highlights for planners the importance of coordinating and integrating all plans and policies to advance the community's vision for heat resilience.
A Call to Action
Heat poses a growing and inequitable threat. Cities around the world must plan now to increase urban heat resilience in the face of climate change and the UHI effect.
Planners are well positioned to use existing regulatory tools and plans to mitigate the inequitably distributed risk associated with the UHI effect, reduce greenhouse gas emissions contributing to climate change, and help prepare for extreme heat events. This PAS Report equips planners with the background knowledge, planning framework, and catalog of comprehensive approaches to heat mitigation and management they need to work effectively with colleagues across agencies and sectors and advance urban heat resilience in their communities.
