4EI Heat Hazard Index

The 4EI Heat Hazard Index from 4 Earth Intelligence (4EI) shows which areas are consistently hotter than their surroundings and so most likely to overheat during a heatwave. The risk is concentrated in cities, where dense buildings and a lack of vegetation or green space create urban heat islands, and councils, planners and emergency responders need to know where it falls hardest.

4EI derives land surface temperature from satellite thermal data, primarily Landsat 8 and 9 (recent work also uses MODIS and ECOSTRESS). It selects cloud-free summer scenes from several years, standardises them across regions and dates, and ranks every location on a scale of 1 to 5; absolute temperatures are not reported. The index is available at 30 m resolution for a whole country or a targeted area anywhere in the world, and as off-the-shelf Heat Hazard Postcode Data for every postcode in Great Britain, built on Ordnance Survey Code-Point with Polygons. Data are supplied as CSV or geospatial files for use in spreadsheets or GIS.

Named users include Bristol City Council, whose heat maps formed part of the evidence base for the Bristol One City Climate Strategy; Climate Ready Clyde, which uses the index in its climate vulnerability map for Glasgow City Region; and Norwich City Council, for which 4EI mapped heat hazard for 2020 to 2025 and classified 51% of the study area as 'High' heat hazard. Early adopters of the free 2020 postcode data included the Greater London Authority, and the London Borough of Lambeth uses the postcode data with OS Open Greenspace in its community engagement platform to help residents find heat refuges. The BBC analysed the GB data alongside deprivation figures. The index was shortlisted for Digital Leaders' Geospatial Innovation of the Year in 2021.