While the summer of 2024 saw global temperatures rise to their highest levels ever recorded, the earth is bracing for even hotter weather. Cities, which are warming at twice the global average due to the urban heat island (UHI) effect, create a cauldron of extreme heat conditions that threaten peoples’ health and safety ­– with lower-income communities affected most. As these extreme heat events become more frequent, longer, and more severe, cities are realizing they need heat action plans.

Planning for extreme heat is complex and should begin long before summer heat kicks in. It should combine the prowess of technical tools and strategic analysis for uncovering patterns and opportunities, with the insight of deep community engagement for understanding peoples’ lived experiences. This dual process helps to prioritize actions and make critical changes where they are needed most. At the same time, to better utilize resources, focus efforts, and enable implementation, plans need to be socialized and activated across a broad base of government, community, and private partners. This whole-systems approach better positions cities to harness and focus their efforts in ways that will protect residents and save lives.

Who feels the heat most?

As our cities grow, the UHI effect is heightened by the loss of natural green infrastructure and the accumulation of materials and structures that trap and emit heat, such as roofs, sidewalks, roads, parking lots, and the metal and concrete of the built environment. The waste heat from buildings, industrial operations, air conditioning units, and vehicles further exacerbates temperatures and the human experience of extreme heat in urban settings.

Across cities, the elderly, children, and those with chronic health conditions are especially at risk in high temperatures, as are outdoor workers and workers confined in hot indoor spaces with no option for relief. Beyond these demographics, historically redlined neighborhoods experience hotter summers than other neighborhoods in 84 percent of major American cities, and sometimes are measurably hotter than wealthier areas of cities — by as much as 12°F during a heatwave. 

This disparity is due to decades of lack of investment, which has deprived these communities of the cooling effects of trees and green spaces, compounding disproportionately high health and pollution burdens. People with lower incomes are also less likely to be able to afford air conditioning, which can save lives in heatwaves.

The preparedness deficiency

For heat mitigation and adaptation strategies to truly support the people with the greatest need, it’s essential to look at both technical data and the lived experience of community members lacking cooling resources.

The public health hazards of urban extreme heat become even more magnified within the context of cities’ lack of preparedness. The Federation of American Scientists references recent research that shows “cities and counties are barreling toward temperature thresholds at which it would be dangerous to operate municipal services, affecting the operations of daily life.” And it notes, very little planning for this future risk is taking place. Indeed, in the US we still lack federal recognition that heat waves are natural disasters, while some countries in Europe are beginning to name their heatwaves, essentially giving them “deadly threat” status.

Given this void at the federal level, it’s not surprising that many cities don’t realize they need a comprehensive plan to effectively address extreme heat. Their emergency services may be siloed from climate action programs or environmental justice initiatives, for example. This lack of coordination can result in inefficiencies, higher costs, and dangerously insufficient responses to heat events. The often-limited staff and constrained budgets of municipal governments further underscore the need for greater collaboration across city agencies and increased organizational integration to optimize resources and response efforts.

Without an overarching heat action plan, cities also lack awareness of which neighborhoods are hottest, what is causing heat impacts, and who is most vulnerable to them. They tend to rely on current or historical data instead of considering projected change. This leaves cities without an understanding of the future impacts of even hotter temperatures on critical systems, such as transportation infrastructure, power grids, and public health.

Heat action plans at a minimum

A city’s heat action plan should extend from early warning measures and emergency response programs to grid and critical systems resiliency strategies. Recovery, which can last days or even weeks, is also an essential part of plans. Paris is planning for future conditions, accelerating measures to adapt to scenarios of 122°F. Future planning can also demonstrate the potential cost of inaction.

Adapting the built environment and infrastructure is a critical part of helping cities mitigate the UHI effect and lower temperatures within buildings. This includes retrofitting buildings with more efficient systems and materials along with using passive strategies to reduce waste heat. Restoring or adding nature-based systems can provide multiple benefits, such as trees and vegetation that cool cities, offer shade, improve air quality, and support biodiversity. Green infrastructure can also provide spongy porous space for mitigating other extreme climate conditions, such as flooding.

City heat action plan

A city’s heat action plan should provide responses both for personal safety during extreme heat events and strategies for cooling the built environment.

 

Technology focuses the picture

To help urban planners and city authorities better understand the causes behind hotter cities and how to cool them down, Arup uses a combination of tools and analysis. Our tool UHeat uses satellite imagery and open-source climate data to calculate the UHI effect at the block or neighborhood level across an entire city. UHeat analyzes key factors contributing to heat buildup in cities, including building heights, surface reflectiveness, the lack of greenery and water, porousness of surfaces, and population density to help identify neighborhoods that are suffering most to model interventions.

To gain a holistic understanding of areas of greatest need and the types of projects that could be most impactful, Arup has developed a geospatial urban resilience tool that integrates many types of physical and demographic datasets. This process can identify areas lacking parks and open space, where marginalized populations are disproportionately at risk. Using results of this analysis, cities can work directly with local populations to find responsive solutions as well as support the case for investment.

The human imperative

For heat mitigation and adaptation strategies to truly support the most vulnerable, cities should integrate technical data with the lived experience of community members lacking cooling resources. Take the example of cooling centers, which can be life savers but are notoriously underused when cities fail to tap into community networks during their development and siting.

To target interventions where they would have the greatest impact for those in greatest need, a 2017 heat action planning guide for Greater Phoenix involved community members in a highly participatory process to create “a local, contextual, and culturally appropriate vision of a safer, healthier future.” In addition to using surface temperature maps with identified hot spots, the process included on-the-ground engagement that followed residents’ routes to work and school to learn what factors influenced where they were comfortable and uncomfortable along the way.

…a whole systems strategy integrates heat action plans into multiple layers of a local government’s operations and organization to maximize resources and impact and create efficiencies.

Among the findings was that all neighborhoods wanted shade added to their walksheds, some along public transportation routes, others along routes to schools. The plan’s solutions included adding shade trees to streets, along with providing bus stops with increased shade for all times of the day, cooler paving, and drinking fountains.

Mainstreaming heat plans

These human and technological strategies for understanding a city’s most concerning extreme heat vulnerabilities should be part of a city’s effort to mainstream heat risk and resilience into its related programs and systems as well as its climate change response. Such a whole systems strategy integrates heat action plans into multiple layers of a local government’s operations and organization to maximize resources and impact and create efficiencies. It also aims to harmonize heat action plans with ongoing climate programs and strategies, such as hazard mitigation planning, to drive solutions with co-benefits and protect against inadvertent inefficiencies.

Arup has been working since 2023 with the City of Los Angeles on their heat action planning efforts to identify the citywide gaps in heat adaptation and public safety and where the city should invest for more integrated and equitable heat resilience. The action plan is coordinated by the City’s Chief Heat Officer (CHO), who also serves as the Director of the Climate Emergency Mobilization Office within the Bureau of Public Works.

Los Angeles’ CHO supports and coordinates efforts across City departments and other agencies related to policies aimed at targeting heat, including the Departments of Emergency Management, Public Works, Water and Power, Recreation and Parks, and the Public Library, among others. Increasingly, CHOs are being appointed in US jurisdictions, such as in Phoenix and Miami-Dade County, and globally to develop and execute heat action plans with other government departments.

Benefits beyond cooling 

Whole systems heat action plans have the potential to go beyond providing healthy solutions for extreme urban heat, especially when cooling interventions involve skills development, provide new jobs, and expand social and business networks. If well supported, community members can leverage this activity to lead and co-create programs for improving quality of life, social cohesion, economic opportunities in their neighborhoods and for the city. In effect, as heat action plans work to save lives and mitigate extreme heat impacts for residents, they can also create stronger communities, which is so critical to surviving and thriving as our planet warms.