Expanding our Heat Resilience data to 50+ global cities

Google Research has expanded its building-level rooftop reflectivity dataset from 14 pilot cities to more than 50 cities across nine countries. By combining Sentinel-2 satellite data with 30-centimeter commercial imagery and machine learning, the project identifies roofs where reflective “cool roof” interventions could reduce urban heat. The data is publicly available through a new Google Earth Engine app for planners and researchers.

Why Rooftop Reflectivity Matters

• Extreme heat contributes to approximately 500,000 deaths annually.
• Urban heat islands make cities warm faster than the global average.
• Dark roofs, pavements, and limited vegetation increase heat absorption.
• Reflective roofs reduce the solar energy absorbed by buildings and can lower local surface temperatures.
• Earlier pilot data from 14 cities supported cool-roof ordinances and broader climate adaptation plans.

Building-Level Albedo Mapping

• Sentinel-2 provides global albedo data but at 10-meter resolution, which cannot reliably distinguish individual rooftops.
• Google Research fused Sentinel-2’s spectral and global coverage with 30-centimeter Airbus Pléiades Neo imagery.
• Machine learning and radiometric calibration reconstruct detailed reflectance profiles at the urban-pixel level.
• Validation against airborne hyperspectral measurements in Boulder, Colorado, produced an RMSE of 0.04.
• The resulting maps allow planners to prioritize large, low-reflectivity buildings for cool-roof retrofits.
• The modeling suggests targeted interventions could reduce extreme urban heat by up to 0.5°C globally.

Heat Resilience Earth Engine App

• Displays building-level albedo using rooftop centroids to highlight low-reflectivity surfaces.
• Provides baseline analyses and supports monitoring changes over time.
• Allows users to download high-resolution data for local studies and policy development.
• Offers a nested view that moves from census-tract summaries to individual buildings.

Expanded Global Coverage

• The dataset now covers more than 50 cities in nine countries.
• Newly included urban areas span Europe, Brazil, and the United States.
• Examples include London, Athens, Barcelona, Rio de Janeiro, São Paulo, Los Angeles, Austin, and New York City.
• The open dataset is intended to help municipalities accelerate reflective-surface programs.

Access and Collaboration

• The interactive app and datasets are publicly available through Google’s Heat Resilience site.
• The methodology is described in the Nature Communications paper “Estimating high-resolution albedo for urban applications.”
• The work was developed by Google Research in collaboration with the World Resources Institute.

Cities can use the app to identify the buildings and neighborhoods where cool-roof investments are likely to have the greatest heat-reduction benefits.