Mean radiant temperature from global-scale numerical weather prediction models

Claudia Di Napoli,Robin J Hogan,Florian Pappenberger

doi:10.1007/s00484-020-01900-5

Abstract

In human biometeorology, the estimation of mean radiant temperature (MRT) is generally considered challenging. This work presents a general framework to compute the MRT at the global scale for a human subject placed in an outdoor environment and irradiated by solar and thermal radiation both directly and diffusely. The proposed framework requires as input radiation fluxes computed by numerical weather prediction (NWP) models and generates as output gridded globe-wide maps of MRT. It also considers changes in the Sun’s position affecting radiation components when these are stored by NWP models as an accumulated-over-time quantity. The applicability of the framework was demonstrated using NWP reanalysis radiation data from the European Centre for Medium-Range Weather Forecasts. Mapped distributions of MRT were correspondingly computed at the global scale. Comparison against measurements from radiation monitoring stations showed a good agreement with NWP-based MRT (coefficient of determination greater than 0.88; average bias equal to 0.42 °C) suggesting its potential as a proxy for observations in application studies.

Highlights

The mean radiant temperature (MRT) is considered the most problematic variable to estimate in the assessment of human biometeorological comfort (Kántor and Unger 2011)
Values were computed for a representative date and time—1st January 2018 at 12UTC—and apply to the calculation of MRT from European Centre for MediumRange Weather Forecasts (ECMWF) numerical weather prediction (NWP) model outputs for accumulation time intervals Δt equal to 3 h or 1 h
These findings extend to the global-scale previous research on the uncertainty of NWP radiation fluxes and its implication to MRT calculation that was assessed at selected European study sites (Schreier and al. 2013)

Summary

Introduction

The mean radiant temperature (MRT) is considered the most problematic variable to estimate in the assessment of human biometeorological comfort (Kántor and Unger 2011). The MRT is a measure of the total radiation from the atmosphere and the ground (radiant environment) incident on an object from all directions. Rather than expressing this measure as a flux density, i.e. the amount of radiation incident on a surface, it is converted into a temperature via the Stefan–Boltzmann equation. The MRT is used to calculate thermal stress indices, i.e. multi-variate parameters describing the overall heat load experienced by the human body when attempting to maintain a thermal equilibrium with the surroundings. Thermal stress indices that require MRT as input parameter are, for instance, the wet-bulb globe temperature (WBGT), the physiological equivalent temperature (PET) and the universal thermal climate index (UTCI) (Budd 2008; Höppe 1999; Błażejczyk et al 2013)

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