Photo: Roman Tiraspolsky

Extreme heat is a grave threat to our cities

Extreme heat poses a far bigger threat to human life than other climate change effects such as extreme flooding, particularly in cities. Between 2000 and 2012, extreme heat was responsible for 162 deaths in New York City alone—almost half of which were attributed to just two events in 2006 and 2011.

Unfortunately, the number of “extreme heat event” days is expected to multiply fivefold in the next 30 years from 11 to 55 days in New York City; from eight to 55 in Newark; and from six to 31 in Hartford. Deaths could double by mid-century.

Heat events also pose significant economic risks. Between 2002 and 2009, heat waves were responsible for $5.2 billion in health costs due to premature deaths, with an additional $179 million due to heat-related illnesses. Communities with large populations of children and the elderly, and households with low incomes are especially at risk for both health and economic impacts.

Although extreme heat kills more people, on average, than any other type of extreme weather event, the majority of adaptation funding provided in recent years has gone toward protecting against storm surges rather than reducing the effects of heat.

Extreme heat can be reduced and managed by making our cities greener and preparing for the inevitable rise in temperatures

Cities and states should employ a variety of strategies to alleviate the heat-island effect in urban communities. These include greening infrastructure, neighborhood-based heat-event relief programs, and the more widespread use of heat-reflective building materials.

Institutionalize greening initiatives and relief programs at the community level

Restoring natural systems, green infrastructure installations, and replacing impervious surfaces with porous pavements are primarily regarded as stormwater management strategies. But they have the additional benefit of reducing urban heat-island effects. These actions also beautify neighborhoods and reduce their carbon footprint. Utilities and municipalities can promote greener neighborhoods by adopting rebate programs like the Portland, Oregon “Treebate” initiative, which provides ratepayers with a credit toward their stormwater and sewer bill for planting a tree on their property. Agencies with jurisdiction over streetscapes can also consider replacing concrete road medians with gardens or lining the street with trees, which helps reduce ambient temperature and stormwater runoff, and improves the quality of life.

Neighborhoods with little greenery and higher concentrations of asthma patients, senior citizens, or low-income residents are particularly vulnerable to extreme heat events. Approximately 93 percent of the most socially vulnerable neighborhoods in our region have high concentrations of impervious surfaces coupled with low amounts of tree coverage, making them very or extremely vulnerable to heat.

Developing community outreach initiatives around extreme heat issues can empower community members and relieve these public health concerns. Community-managed rooftop gardens and street-tree initiatives can provide work for local residents, as well as cool the buildings they cover. Heat-stress initiatives can be incorporated into grade-school curriculums to encourage smart decisions about outdoor activity during extreme heat events. Officials should target these initiatives toward neighborhoods identified by RPA’s Heat Vulnerability Analysis.

Require major urban projects to be green

Extreme heat can be mitigated by adjusting how we design and construct our built environment. Buildings in urban areas need to adopt robust building-code standards that put more focus on efficient insulation to minimize air conditioning usage during summer months, when stress on the electrical grid is highest. In addition, developers, state agencies, and regional transportation agencies should replace highly absorbent infrastructure materials with more reflective ones wherever feasible. For example, “white-topping” an asphalt roadway with concrete overlays to increase the streetscape albedo has been done on highways surrounding Denver, Colorado. Planning for urban streetscapes should also include using permeable and water-retentive pavements in select areas, such as truck-restricted corridors and pedestrian-only walkways.

Use pilot programs to measure the impact of natural approaches, and design community-based solutions

State agencies and planning officials should develop pilot programs that expand urban forestry, green infrastructure, and stream daylighting approaches, measuring the cooling effect on ambient temperature of immediate surrounding areas. This would help municipalities identify nature-based cooling solutions that would work best for their communities, while also developing a better case for utilizing green infrastructure solutions for stormwater and extreme-heat mitigation. Measuring effects on multiple scales could inform how future projects’ success is defined, and to inform the parameters of innovative financing mechanisms like social-impact bonds. Understanding a project’s effect on the cooling and water management of a community facilitates implementation of and investment in later projects.

Trees, green roofs, and other vegetation can help cool urban communities by deflecting radiation from the sun and releasing moisture into the atmosphere. Image: Only If + One Architecture for RPA’s 4C Initiative


A proactive approach toward cooling our region’s communities would yield opportunities for critical and multiple benefits to arise, including:

  • Reduced heat stress in vulnerable communities and heat-related fatalities during extreme heat events
  • Improved knowledge about heat-mitigation strategies
  • Reduced stormwater runoff
  • More attractive public spaces, which in turn could encourage economic investment into the area and uplift communities
  • More jobs in low-income communities to green buildings and public spaces
  • Stronger ties among community members who work together at community gardens and other outdoor spaces

Paying for it

State and local expenditures in the form of tax breaks, utility rebates, and other financial incentives, such as cool roofs and better building materials, would leverage localized UHI-mitigation strategies. Meanwhile, large-scale mitigation strategies such as increasing the urban tree canopy, replacing streets with “cool pavements,” and installing green infrastructure will require large investments from municipal, state, and federal governments, as well as nonprofits. For example, New York City’s Million Trees Initiative was able to meet its goal two years ahead of schedule and with expansive reach, with help from the nonprofit New York Restoration Project, which raised $30 million to implement the plan. Municipalities will also need to account for the ongoing maintenance costs of these projects. Some projects that have multiple benefits, such as climate adaptation or stormwater management, could leverage funding from federal or other sources that might be more readily available to implement cooling measures. These high up-front investments could help control healthcare expenditures in vulnerable communities and spur more economic investment in “newly green” communities.

1. New York City Department of Health and Mental Hygiene, “Epi Data Brief,” 2014
2. The National Resources Defense Council, “Killer Summer Heat,” 2012
3. The National Resources Defense Council, “Health and Climate Change: Accounting for Costs,” 2011
4. Centers for Disease Control and Prevention, “Climate Change and Extreme Heat Events,” 2016
5. Public Health Institute and Center for Climate Change and Health, “Extreme Heat, Climate Change and Health,” 2016
6. Madrigano, Jaime et al., “A Case-Only Study of Vulnerability to Heat Wave–Related Mortality in New York City (2000–2011),” Environmental Health Perspectives, 2015