Heat stress - Cities and FUAs

This dataset provides an indicator of population exposure to heat stress.

Data sources and methodology

The indicator uses the Universal Thermal Comfort Index (UTCI). The UTCI enables to assess the impact of atmospheric conditions on the human body by considering air temperature, wind, radiation and humidity. UTCI values from 32°C to 38°C are considered as strong heat stress, from 38°C to 46°C as very strong heat stress, and above 46°C as extreme heat stress. Population exposure to heat stress was computed using the hourly thermal comfort indices grids from the Copernicus Climate Data Store (Di Napoli C. et al.). For each 0.25° by 0.25° grid cell, the number of days for which the maximum UTCI value is above each heat stress threshold (32°C, 38°C and 46°C) is computed. FUA and city level indicators correspond to the population-weighted average number of days above each heat stress threshold, obtained by intersecting the computed grid with the Global Human Settlement Population layer (European Commission, GHSL Data Package 2023).

These estimates may differ from official subnational climate statistics due to differences in methodological approaches, such as the use of reanalysis based top down modelling versus in situ observations, along with variations in input data sources, spatial resolution, and the models and algorithms used to generate temperature estimates.

Defining FUAs and cities

The OECD, in cooperation with the EU, has developed a harmonised definition of functional urban areas (FUAs) to capture the economic and functional reach of cities based on daily commuting patterns (OECD, 2012). FUAs consist of:

1. A city – defined by urban centres in the degree of urbanisation, adapted to the closest local administrative units to define a city.


2. A commuting zone – including all local areas where at least 15% of employed residents work in the city.

The delineation process includes:

• Assigning municipalities surrounded by a single FUA to that FUA.


• Excluding non-contiguous municipalities.

The correspondence table between SAUs and FUAs/cities is available in parquet and csv format.
The definition identifies 1 272 FUAs and 1 269 cities in all OECD member countries except Costa Rica and three accession countries.

Cite this dataset

OECD Regions, cities and local areas database (Heat stress - Cities and FUAs), http://oe.cd/geostats

Further information

• OECD Local Data Portal


• OECD Regions and Cities at a Glance

For questions and/or comments, please email [email protected]