On the Measurement of Heat Waves

TLDR

Heat‑wave definitions and measurements are ambiguous and inconsistent, often limited to the affected group or the study reporting them. This study seeks to resolve this by applying three heat‑wave definitions derived from a survey of climate‑science indices. The definitions require at least three consecutive days exceeding the 90th percentile of maximum or minimum temperature or a positive extreme heat factor, and each is evaluated with a multiaspect framework that records number, duration, participating days, peak and mean magnitudes. For Australia, Sen’s Kendall slope estimator shows that trends for all aspects are smaller but more significant in 1951–2008 than 1971–2008, with intensity rising faster than mean magnitude, and the results suggest that the number of heat‑wave days drives event frequency, while the methodology is broadly applicable and offers a range of useful definitions.

Abstract

Abstract Despite their adverse impacts, definitions and measurements of heat waves are ambiguous and inconsistent, generally being endemic to only the group affected, or the respective study reporting the analysis. The present study addresses this issue by employing a set of three heat wave definitions, derived from surveying heat-related indices in the climate science literature. The definitions include three or more consecutive days above one of the following: the 90th percentile for maximum temperature, the 90th percentile for minimum temperature, and positive extreme heat factor (EHF) conditions. Additionally, each index is studied using a multiaspect framework measuring heat wave number, duration, participating days, and the peak and mean magnitudes. Observed climatologies and trends computed by Sen's Kendall slope estimator are presented for the Australian continent for two time periods (1951–2008 and 1971–2008). Trends in all aspects and definitions are smaller in magnitude but more significant for 1951–2008 than for 1971–2008. Considerable similarities exist in trends of the yearly number of days participating in a heat wave and yearly heat wave frequency, suggesting that the number of available heat wave days drives the number of events. Larger trends in the hottest part of a heat wave suggest that heat wave intensity is increasing faster than the mean magnitude. Although the direct results of this study cannot be inferred for other regions, the methodology has been designed as such that it is widely applicable. Furthermore, it includes a range of definitions that may be useful for a wide range of systems impacted by heat waves.