A recent increase in long-lived heatwaves in China under the joint influence of south Asia and western north pacific subtropical highs

Abstract

Long-lived ($6 days) heatwaves (HWs) have strong social impacts with serious health implications. Using homogenized historical daily temperatures from China and ECMWF reanalysis data, this study investigates its frequency between 1979 and 2018 and driving mechanisms. It is found that the occurrence of HWs is strongly associated with the joint actions of the South Asian high and the western North Pacific subtropical high, which can be described by a synergy index measured by the boundary distance between the two subtropical high pressure systems. When the synergy index is positive, there are more long-lived HWs in the east of the Tibetan Plateau, the lower reaches of the Yangtze River, and the southern region in China, and vice versa. A Mann-Kendall test shows a significant interdecadal shift around 2004/05 toward increased occurrence that is consistent with enhanced subtropical high systems. This study shows the important roles of large-scale dynamic systems in regional climate extremes and their future changes.