Cities are hot — sometimes between 5 and 9 degrees F warmer than surrounding rural areas — and they’re getting hotter. On average, cities are warming at twice the global rate. A major reason for this is the way many cities are built, with an abundance of dark, heat-absorbing surfaces and a lack of cooling vegetation. This urban heat island effect can exacerbate challenges that many cities are already experiencing as temperatures rise, from deadly health impacts to productivity loss, increased energy demand and infrastructure damage.

But there are steps that cities can take to reduce the impacts of urban heat and to help keep residents safe. Implementing cooling infrastructure like trees and reflective pavements — so-called “smart surfaces” — is one effective strategy. Smart surfaces reduce temperatures by changing the way energy from the sun interacts with the built environment of cities.

WRI, as a data partner in the Cities for Smart Surfaces project (part of the Smart Surfaces Coalition), is helping enable more cities to utilize smart surfaces by mapping where implementation can occur and providing a baseline against which to measure change. 

By combining open and globally available data from OpenStreetMap and satellite imagery, WRI is mapping surfaces — like roads, buildings, parking lots and public open space — that influence heat dynamics. Along with satellite remote sensing, we use this data to map the reflectivity, tree cover and vegetative cover of cities, allowing us to characterize current conditions and identify opportunities for implementing green and reflective infrastructure.

While this work focuses on U.S. cities, the methodologies are relevant globally, and we are currently scaling them to assess the potential for improving heat resilience in partner cities participating in our Data for Cool Cities project.

WRI works with the broader Smart Surfaces Coalition to advance understanding of urban surface conditions and potential for heat mitigation in three key ways:

  • Mapping urban land use and land cover in ways that are most useful to cities. Not all cities have access to high-resolution maps of their built environment. We use only freely available data to improve access and equity for all cities in the U.S. To account for the fact that most existing land use and land cover data does not contain the kinds of features where smart surfaces can be implemented (such as roads, buildings and parking lots), we created methods to specifically capture these categories. 

  • Quantifying the characteristics of surfaces that influence heat, focusing on reflectivity and vegetation. We measure the reflectivity of surfaces like roofs, roads and parking lots and assess the percentage of existing tree and vegetation cover in cities. This generates baseline data from which to assess progress on heat mitigation. This level of detail helps cities understand the potential of specific surfaces to mitigate heat.

  • Providing clear, accessible, data-backed information to help cities make progress. While the dynamics of urban heat are complicated, there are new methods and models that can help. We equip cities with new data and actionable interpretations of that data so they can develop effective and context-specific heat policies.