Verification of Heat Stress Thresholds for a Health-Based Heat-Wave Definition

Florian Pappenberger,Hannah L. Cloke,Claudia Di Napoli

doi:10.1175/jamc-d-18-0246.1

Abstract

AbstractHeat waves represent a threat to human health and excess mortality is one of the associated negative effects. A health-based definition for heat waves is therefore relevant, especially for early warning purposes, and it is here investigated via the universal thermal climate index (UTCI). The UTCI is a bioclimate index elaborated via an advanced model of human thermoregulation that estimates the thermal stress induced by air temperature, wind speed, moisture, and radiation on the human physiology. Using France as a test bed, the UTCI was computed from meteorological reanalysis data to assess the thermal stress conditions associated with heat-attributable excess mortality in five cities. UTCI values at different climatological percentiles were defined and evaluated in their ability to identify periods of excess mortality (PEMs) over 24 years. Using verification metrics such as the probability of detection (POD), the false alarm ratio (FAR), and the frequency bias (FB), daily minimum and maximum heat stress levels equal to or above corresponding UTCI 95th percentiles (15° ± 2°C and 34.5° ± 1.5°C, respectively) for 3 consecutive days are demonstrated to correlate to PEMs with the highest sensitivity and specificity (0.69 ≤ POD ≤ 1, 0.19 ≤ FAR ≤ 0.46, 1 ≤ FB ≤ 1.48) than minimum, maximum, and mean heat stress level singularly and other bioclimatological percentiles. This finding confirms the detrimental effect of prolonged, unusually high heat stress at day- and nighttime and suggests the UTCI 95th percentile as a health-meaningful threshold for a potential heat-health watch warning system.

Highlights

The summer of 2003 represented a turning point in the study of heat waves and their impacts on human health
universal thermal climate index (UTCI) maps derived from the 1979–2002 ERAInterim data (50th percentile) show the summer thermal bioclimate of France is characterized by a specific time and spatial variability (Fig. 2a)
Minimum UTCI values follow a similar pattern with northern regions characterized by slight cold stress conditions and southern regions experiencing no thermal stress

Summary

Introduction

The summer of 2003 represented a turning point in the study of heat waves and their impacts on human health. Days identified via epidemiological studies with heat-attributable excess mortality can be used to characterize heat stress thresholds hazardous to health Following this rationale, the present paper aims 1) to investigate the UTCI as a heat-health indicator able to define and recognize heat stress conditions responsible for the mortality burden associated with heat waves, and 2) to assess the relative advantage of using a bioclimatological index for heat-health warning systems with respect to single variables, that is, air temperature. From there UTCI thresholds have been calculated at different percentiles and tested using verification metrics in their ability to identify days when excess mortality due to heat has been observed

Data and methods

Discussion

Conclusions