Inter-Comparison of Diverse Heatwave Definitions in the Analysis of Spatiotemporally Contiguous Heatwave Events over China

Abstract

A heatwave (HW) is a spatiotemporally contiguous event that is spatially widespread and lasts many days. HWs impose severe impacts on many aspects of society and terrestrial ecosystems. Here, we systematically investigate the influence of the selected threshold method (the absolute threshold method (), quantile-based method (), and moving quantile-based method ()) and selected variables (heat index (), air temperature ()) on the change patterns of spatiotemporally contiguous heatwave (STHW) characteristics over China from 1961–2017. Moreover, we discuss the different STHW change patterns among different HW severities (mild, moderate, and severe) and types (daytime and nighttime). The results show that (1) all threshold methods show a consistent phenomenon in most regions of China: STHWs have become longer-lasting (6.42%, 66.25%, and 148.58% HW days () increases were found from 1991–2017 compared to 1961–1990 corresponding to , , and , respectively, as below), more severe (14.83%, 89.17%, and 158.92% increases in HW severity () increases), and more spatially widespread (14.92%, 134%, and 245.83% increases in the summed HW area ()). However, the HW frequency () of moderate STHWs in some regions decreased as mild and moderate STHWs became extreme; (2) for threshold methods that do not consider seasonal variations (i.e., and ), the spatial exceedance continuity was relatively weak, thus resulting in underestimated STHW characteristics increase rates; (3) for different variables defining STHWs, the relative changing ratio of the -based STHW was approximately 20% higher than that of the -based STHW for all STHW characteristics, under the threshold; (4) for different STHW types, the nighttime STHW was approximately 60% faster than the daytime STHW increase considering the threshold and approximately 120% faster for the method. This study provides a systematic investigation of different STHW definition methods and will benefit future STHW research.

Contribution of Anthropogenic Activities to the Intensification of Heat Index‐Based Spatiotemporally Contiguous Heatwave Events in China

“…Specifically, while Tibet has a lower HWI compared to eastern regions, it compensates with an extended HWD, culminating in an HWS severity level commensurate with that in Yunnan and Guangdong provinces. Inconsistencies in the monthly temperature rise throughout the year can disrupt the temporal continuity of HI‐STHW events (Song et al., 2022, their Figures 4 and 8). We guess that consistent monthly temperature rise is the reason for the higher HWD in Tibet.…”

“…While we considered the whole year, and mainly focused on the annual most severe HI‐STHW events, which produces longer HWD and HWA sum . (b) The faster increasing speed in HI max (J. Li et al., 2018; Song et al., 2022): We used HI max to define STHWs, while (Luo, Lau, et al., 2022) used T max . The increasing trend of HI max is stronger than that of T max in 62.4% of the regions of China (Figure S12c in Supporting Information ), and the China area‐weighted HI max increased at a rate of 0.023°C/decade faster than T max during 1961–2014 (Figure S12d in Supporting Information ).…”

“…Grids experiencing HWs are identified when the corresponding HI ≥ threshold (TRS). Song et al (2022) revealed that threshold methods (e.g., the fixed threshold) that do not consider seasonal variations will weaken the continuity of HI exceedance and underestimate the increasing rate of STHW. In this study, we used a seasonally varying TRS.…”