Background information

Background Information

The Universal Thermal Climate Index (UTCI) days index is relevant to human health. This Index is part of the Extreme Heat Hazard type of the Heat and Cold category of the classification.

The index gives the number of days with either strong, very strong and extreme heat stress.

A higher value indicates more High UTCI days and thus more stress on human health caused by perceived heat conditions.


The count of days when UTCI remains above 32°C (Number of days).

The UTCI is an equivalent temperature (°C) and is a measure of the human physiological response to meteorological conditions that also takes into consideration the clothing adaptation of the population in response to outdoor temperature. It is based on four surface variables: air temperature, relative humidity, wind speed and mean radiant temperature.

UTCI values are divided in 5 classes of heat stress: no thermal stress (9°C-26°C), moderate heat stress (26°C-32°C), strong heat stress (32°C-38°C), very strong heat stress (38C°-46C°), and extreme heat stress (>46°C).

Data Sources

The data was assembled on behalf of the Copernicus Climate Change Service (C3S) based on reanalysis data hosted on the C3S Climate Data Store (CDS).

The index is extracted from a dataset based on the ERA5 reanalysis. ERA5 is regarded as a good proxy for observed atmospheric conditions and currently covers 1959 to near real time and is regularly extended as ERA5 data become available. There are no climate projections of UTCI at the moment. (link)

Supporting Information

Further information about this application can be found in the Product User Guide (PUG) of the application in the documentation resources of the CDS.

Related information can also be found on other sections of the EEA site: The Index based interactive EEA report: Heat and cold — extreme heat (link).

Data download

The aggregated data shown on the map can be downloaded as csv files.

The application has an interactive map on the left side with a set of drop down menus to select the regions (NUTS, Transnational regions or Europe Zones), the time span (Year, Season or Month) and the emission scenario (RCP4.5 or RCP8.5). By clicking on the map, a scrolling panel appears on the right side displaying interactive plots corresponding to spatial and temporal averages over the selected region. Hover over the plots to see the values. Some plots show an uncertainty envelope representing the range of likely values, as defined by the IPCC, based on an ensemble of models (see FAQ).

Content in the European Climate Data Explorer pages is delivered by the Copernicus Climate Change Service (C3S) implemented by ECMWF.


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This translation is generated by eTranslation, a machine translation tool provided by the European Commission.