Evaluating the Time of Emergence of Heat Waves using Different Definitions

Abstract

Heat extremes, such as heat waves, are characterized by human health effects, increased mortality, and ecosystem-wide impacts. Previous studies of heat waves do not define when and where heat wave frequency will be distinguishable from the background frequency of heat waves in the coming century, and previous studies of heat extremes do not analyze how varying the definition of heat waves contribute to emergence. Using daily resolution of 10 CMIP6 era General Circulation Models forced by the SSP2-4.5 warming scenario, we evaluate the frequency of two definitions presented by the Intergovernmental Panel on Climate Change (IPCC) of heat waves in a reference period and in the future climate to determine the “time of emergence”, or the time when the frequency of heat waves becomes perceptibly different from the background frequency. For heat waves that exceed 5°C above the historical climatology, time of emergence is earliest in high latitude regions and is most correlated with the signal. For heat waves that exceed the 90th percentile of the historical climatology, time of emergence is earliest in low latitude regions and is most correlated with the signal to noise ratio. Identifying the time of emergence for the frequency of heat waves can contribute to potential mitigation policies and techniques that are region and time specific.