Thermal comfort indices time-series derived from ERA5 reanalysis
General description
This dataset, provides modelled hourly data and is stored in Analysis Ready Cloud Optimised (ARCO) format, which has been implemented for retrieving long time-series for a single point in a efficient way. It provides modelled hourly data for a set of indices representing human thermal stress and discomfort in outdoor conditions. The dataset is organised around two main variables, the mean radiant temperature and the universal thermal climate index. These are calculated from environmental parameters (air temperature, humidity, wind speed, radiation) provided by ECMWF ERA5 reanalysis. The dataset is regularly extended with time as ERA5 data become available.
A throughout description of the database can be found in:
Di Napoli C, Barnard C, Prudhomme C, Cloke HL and Pappenberger F (2021) ERA5-HEAT: A global gridded historical dataset of human thermal comfort indices from climate reanalysis. Geoscience Data Journal 8: 2–10. https://doi.org/10.1002/gdj3.102 |
Methodology
The process to generate this dataset involves:e
- Fetching UTCI data in NetCDF format.
- Written to an ARCO Zarr archive (which is similar in structure to netCDF)
- The CDS requests the data from the Zarr archive using xarray and writes the data to netCDF or CSV (as requested).
Data organization and access
The ARCO data is stored as Zarr datacubes.
The data is now available from the Climate Data Store (CDS), either interactively through its download web form or programmatically using the CDS API service:
Thermal comfort indices time-series derived from ERA5 reanalysis
Spatial grid
The parameters have a grid of 0.25 degrees.
Please be aware when you select a "Location" on the form, the latitude and longitude values are rounded to the closest neighbourhood point of the 0.25 degrees grid.
Temporal frequency
Temporal frequency of the data is hourly and every day has 24 hourly steps.
Data format
In the CDS, there are the options of retrieving the data in netCDF format or CSV format.
Thermal comfort indices descriptions
Universal thermal climate index (UTCI): The UTCI is a state-of-the-art indicator that estimates the thermal stress the human body undergoes when exposed to outdoor conditions. The UTCI is an international standard developed by the European Cooperation in Science and Technology (COST) Action 730. It is defined as the air temperature of a reference outdoor environment that would elicit in the human body the same physiological response (sweat production, shivering, skin wettedness, skin blood flow and rectal, mean skin and face temperatures) as the actual environment.[1] Since its creation in 2009 the UTCI has been evaluated across different climate regions, from urban to global scales, as well as deployed as reference variable in weather forecasts and climate projections.
Mean radiant temperature (MRT): The MRT is the uniform temperature of a fictive black-body radiation enclosure which would result in the same net radiation energy exchange with a human subject as the actual, more complex radiation environment (Figure 1). The MRT is an international standard for thermal environment ergonomics according to the International Organization for Standardization.[2] It also a standard for thermal environmental conditions for human occupancy according to the American Society of Heating, Refrigerating and Air-Conditioning Engineers.[3]
Figure 1 Graphical explanation of the mean radiant temperature (MRT). Adapted from [4].
Summary variable table
Variable | Description | UNIT |
Mean radiant temperature | Numerical representation of how human beings experience radiation. It applies to a human subject placed in an outdoor environment and irradiated by solar and thermal radiation both directly and diffusely. | K |
Universal thermal climate index | Numerical representation of the thermal comfort/discomfort perceived by a human subject when exposed to outdoor conditions. It is based on a state-of-the-art model that simulates human body’s physiological responses to air temperature, humidity, wind speed and radiation. | K |
Thermal comfort indices algorithm
The dataset is computed via a sequence of well-defined, computer-automated steps (algorithm, Figure 2). The algorithm takes as input the following ERA5 reanalysis atmospheric variables: air temperature and relative humidity (from dew point temperature) at 2 meters above the ground, wind speed at 10 meters above ground level and radiation fluxes at the Earth’s surface. Radiation fluxes - both solar and thermal - are used to calculate the MRT by taking into account the time period in which modelled radiation is accumulated and the Sun’s position changes.[5] The MRT, air temperature, relative humidity and wind speed are input into a multi-variable equation which has the UTCI as a result.[6] The outputs of the algorithm (products) are hourly reanalysis data of MRT and UTCI at the global scale (except Antarctica).
Figure 2 Workflow of the thermal comfort indices algorithm.
Data Availability
The algorithm generates MRT and UTCI products as soon as reanalysis input data are released.
The data was produced based upon the Consolidated dataset available at the time of production and then further extended with the Intermediate dataset.
Data Availability for ERA5 is from 19400103 until 5 days behind realtime.
The Timeseries will continue to be extended by the intermediate dataset when it becomes available.
When Consolidated data becomes available, the intermediate data within the timeseries will be replaced, we will add here if there are any differences to the intermediate and consolidated.
Users should consider that any intermediate data is subject to change.
Available Versions
The Timeseries is based upon the Consolidated dataset and Intermediate extension of Version 1.1 of the original dataset.
[1] Jendritzky G, de Dear R, Havenith G (2012) G. UTCI—Why another thermal index?, International Journal of Biometeorology 56:421. https://doi.org/10.1007/s00484-011-0513-7
[2] ISO 7726. Ergonomics of the thermal environment - Instrument for measuring physical quantities. Geneva, Switzerland: International Organization for Standardization. November 1998
[3] ANSI/ASHRAE Standard 55-2017, Thermal environmental conditions for human occupancy, ISSN 1041-2336
[4] Kántor N and Unger J (2011) The most problematic variable in the course of human-biometeorological comfort assessment — the mean radiant temperature, Central European Journal of Geosciences 3: 90. https://doi.org/10.2478/s13533-011-0010-x
[5] Di Napoli C, Hogan RJ, Pappenberger F (2020) Mean radiant temperature from global-scale numerical weather prediction models, International Journal of Biometeorology, https://doi.org/10.1007/s00484-020-01900-5
[6] Bröde P et al. (2012) Deriving the operational procedure for the Universal Thermal Climate Index (UTCI) International Journal of Biometeorology 56:481. https://doi.org/10.1007/s00484-011-0454-1
