Shown on the map above is the monthly average of daily maximum of Universal Thermal Climate Index (UTCI)9, a variable that captures the physiological capability of the human body to maintain its own temperature, in a process known as thermoregulation. UTCI is expressed in degrees and depends on air temperature, humidity, wind and radiation.
Past values of UTCI can be obtained from ECMWF's Climate Data Store. The ERA5-HEAT dataset7 provides hourly values of UTCI since January 1979, with 0.25° resolution and coverage from 60° S to 90° N, based on the ERA5 reanalysis dataset.
Climate projections of UTCI included in this story correspond to monthly means of daily maximum fields. For the calculation of UTCI, 4 physical variables evaluated at the Erath surface are used: 2-metres temperature, 2-metres humidity, 10-metres wind speed and mean radiant temperature (whose estimation involves several components of the solar and thermal radiation10). In order to compute UTCI fields with the data available on the CDS, we have implemented the following approach: Daily fields of humidity, wind and daily maximum temperature have been used from the CIMP5 daily data on single levels dataset (1971-2100). For the computation of the mean radiant temperature (MRT), which requires hourly resolution fields not available on the CDS for climate projections, climatological monthly means of daily maximum MRT have been used directly computed from the hourly ERA5-HEAT dataset. A validation of this approach have been carefully performed showing that the corresponding error is well below the inner uncertainty of the official UTCI dataset tending to zero when monthly averaging. Currently, UTCI projections are calculated for the RCP8.5 scenario using the ACCESS1-0 model after being bias corrected.
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10 Di Napoli, C., Hogan, R.J., Pappenberger, F. (2020): Mean radiant temperature from global-scale numerical weather prediction models. International Journal of Biometeorology, 64, 1233–1245. DOI: 10.1007/s00484-020-01900-5.