Reducing Our Risk

The Trust for Public Land

Entry Overview

As roads, buildings, and built infrastructure replace open space in a city, the concrete, steel and other building materials that go into these projects retain heat and create a dramatically warmer environment than is found in surrounding rural and suburban areas. This is known as the “Urban Heat Island (UHI) effect,” which will only be intensified by increases in air temperature due to climate change. The National Climate Assessment identifies UHI’s, combined with an aging population and increased urbanization, as a major concern for public health, increasing the vulnerability of urban populations to heat‐related impacts in the future. One way cities can remedy or reduce the impact UHIs have on communities is to deploy shade trees and specially-designed features like green alleys in high need areas. The Trust for Public Land has developed the Urban Heat Risk Explorer App to educate residents of cities about their risk to extreme heat events and opportunities to take action.

General Info
Email :
Organization Address: 
101 Montgomery Street #900
San Francisco, California 94104
United States
Population Impacted: 
Extreme Temperature
Identify the likelihood and frequency of this hazard : 
We explored heat risk factors in cities across the US and selected five cities suffering from heat-related issues or projected future issues. Chattanooga, for instance, was selected because mean annual temperatures are projected to increase across the Southeast through the 21st century. Eastern Tennessee’s average annual temperature is projected to increase by 4-5 degrees by mid-century. Models show that Chattanooga will likely experience upwards of 35 days with temperatures exceeding 95 degrees.
Explain how vulnerable the community is to this hazard: 
The National Climate Assessment identifies UHI’s, combined with an aging population and increased urbanization, as a major concern for public health, increasing the vulnerability of urban populations to heat‐related impacts in the future. UHIs have a disproportionate impact on the young, elderly, and vulnerable populations.
List the potential affects of this hazard: 
UHI’s have a number of adverse impacts on communities such as increasing summertime peak energy demand, air conditioning costs, air pollution and greenhouse gas emissions, illness, mortality, and degrading water quality. One study found that the UHI effect necessitates an extra 5‐10% of energy use for cooling urban buildings during peak energy use periods. This has important climate change impacts, as extra energy used for cooling results in additional GHG emissions, a cycle that will increase global air temperatures and urban heat challenges.
Identify how sensitive the community is to these affects: 
The intense heat wave that struck Chicago, Illinois in 1995 provided an example of potential heat‐related threats in the future, with 750 deaths attributed to this event. In fact, heat waves kill more Americans each year than any other kind of natural event.
Preparedness Goal: 
The Trust for Public Land combined the best available data create an interactive web-based application that map out the areas in highest need of green infrastructure in five US cities.
Implementing Actions: 

The Trust for Public Land has created a web based application that maps Urban Heat Islands in five US cities. This application identifies the places of greatest need for urban greening by integrating two aspects of vulnerability: 1) where new green assets will have the greatest structural impact to reduce climate‐driven public safety threats like flooding and heat; and 2) where there are populations with the highest social and demographic vulnerability to future threats. Climate‐Smart Cities efforts are most strategic and impactful when directed to neighborhoods and project sites where these risk factors converge.

Primary objectives for mapping UHI’s include:

  1. Identify spatially explicit opportunities where strategic green infrastructure intervention can help mitigate the impacts of heat islands in urban areas, such as higher energy usage and heat‐related illnesses.
  2. Educate partner cities and conservation practitioners by providing visual products that help translate UHI science to real, on‐the‐ground conditions in their neighborhoods.
  3. Create a mapping methodology that is efficient, defensible, and comparable across North American urban areas, and that is replicable from city to city regardless of location, geography, and scale.

The Trust for Public Land currently depicts UHI isotherms using a methodology that incorporates land surface temperature (LST) data obtained and preprocessed from the Moderate Resolution Imaging Spectro (MODIS) radiometer satellite. By focusing on MODIS as the primary LST input, UHI analysis across multiple urban areas is repeatable and comparable, and requires only modest data preprocessing. To date, The Trust for Public Land has analyzed and mapped UHI isotherms for five North American cities using this methodology described above. Cities include Chicago, Los Angeles, New York City, Denver, and Chattanooga. The maps provided in the ‘photos’ section of this application depict results from these analyses. For more detailed results in an interactive mapping format, please see

Describe Your Solution: 

The Trust for Public Land’s Climate‐Smart Cities program is bringing nature and nature‐based systems back into cities to slow climate change and lessen its impacts. The Trust for Public Land has been weaving natural elements back into American cities big and small for our entire 40‐year history—creating “green infrastructure” to complement cities’ built infrastructure.

Now we are directing our urban greening efforts into a science‐based Climate‐Smart Cities strategies to lower carbon emissions and protect cities from climate risks like sea level rise, flooding, and heat waves. We are consulting with city leaders and scientists to develop a national strategy focused on four aspects of Climate‐Smart Cities:

  • Connect: Link walk‐bike corridors and public transit lines into integrated networks that provide residents with safe, accessible, and carbon‐efficient transportation options.
  • Cool: Deploy shade trees and specially‐designed features like green alleys to reduce Urban Heat Island impacts.
  • Absorb: Utilize wetlands, “water smart” parks, and other green infrastructure to recharge urban aquifers and naturally manage stormwater runoff with lower carbon emissions from treatment.
  • Protect: Create scientifically‐sited and designed green buffers, such as waterfront parks and wetlands, to protect cities from sea level rise, coastal storms, and extreme rainfall events.

Deploying new green features to protect cities from climate risks will have important public safety benefits for the 80 percent of Americans living in urban areas, particularly vulnerable populations like the elderly, disabled, and economically disadvantaged. These populations are at higher risk for climate threats like heat illness, yet often live in neighborhoods that offer less natural protection such as shade trees to lessen the Urban Heat Island effect. The Urban Heat Risk Explorer App has been developed to engage residents and increase their awareness about their potential risk and action they can take  and advocate for in their city.

  • Green infrastructure increases the quality of life for urban residents, encouraging more people to live in urban areas. Residents of urban areas have lower carbon emissions per capita than suburban residents.
  • The use of trees and shrubs near buildings (both as shading and wind breaks) can help manage temperature extremes and reduce HVAC costs.
  • Green infrastructure, such as wetlands and parks, within riverine floodplains can reduce peak volumes of flood water and provide areas where flooding will cause less damage.
  • Coastal green infrastructure, such as wetlands and dunes, can act as a storm surge buffer and slow inundation.
  • Green infrastructure that provides space for new trees to be planted allows trees capture and store carbon.
  • Green infrastructure also increases infiltration into urban soils and decreases erosion, allowing urban soils to retain the carbon currently stored.
  • Green infrastructure helps reduce other atmospheric pollutants that have an impact on climate, such as ground level ozone and particulate matter.
  • Green infrastructure helps mitigate stormwater flooding by capturing, filtering and/or infiltrating runoff from nearby impermeable surfaces.
  • Green infrastructure can play a role in helping wildlife adapt by conserving strategic existing green space and providing better integrated networks of key habitats.
  • Green corridors and networks provide walking and cycling routes which promotes active travel and reduces carbon emissions.
  • Green infrastructure can have a positive impact on the health of urban residents by providing shade and cooler spaces for outdoor recreation, reducing flood risks, maintaining air quality, and reducing the urban heat island effect.
  • The planning process for green infrastructure investments provides an opportunity to educate the community and increase understanding about risks and how local decisions help mitigate or perpetuate those risks, as well as foster community cohesion and support.
What were the negative or unintended impacts (if any) associated with implementing this solution? : 


Return on Investment: How much did it cost to implement these activities? How do your results above compare to this investment?: 

The Urban Heat Risk Explorer was initially developed as part of Environmental Systems Research Institute’s Resilience Application Challenge. The Trust for Public Land in actively adding additional cities to the App (at ~$1,000 per city). There is additional cost to successfully engaging city resident in use of the application and subsequently implementing green infrastructure on the ground to help address UHIs. We have taken the first step by investing our own resources in the development of this application. Taking it to the next level and engaging city residents to help promote action is the next step.

What are the main factors needed to successfully replicate this solution elsewhere?: 

The main factors to successfully replicating this solution elsewhere include the need to identify a willing local partner to help us pilot the application at the neighborhood level. We also are committed to expanding the number of data available through the application and the functionality.

Contest Info
Contest Name: 
Reducing Our Risk

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