Factor analysis of recent major heatwaves in East Asia

Heatwaves (HWs) present a major hazard to our society and more extreme heatwaves are expected with future climatic changes. Hence, it is important to improve our understanding of the underlying processes that drive HWs, in order to boost our socioeconomic-ecological resilience. In this study, we quantified the influences of key driving factors (large-scale atmospheric circulation, soil moisture, and sea surface temperature) and their synergies on recent heatwaves in East Asia. We conducted a factor separation analysis for three recent HW events by constraining the key factors in the regional Weather Research and Forecasting model with their climatologies or pseudo-observations in different combinations. Our study showed distinct spatial variations in the HW-controlling factors in East Asia. The synergistic interaction of large-scale circulation and soil moisture was the most important factors in the 2013 Chinese HW. During the 2018 HWs in Korea and Japan, the same stagnant large-scale atmospheric circulation played a dominant role in driving the HW events. The land-atmosphere coupling via soil moisture, its interaction with circulation, and SST exhibited stronger influences during the Korean HW than the Japanese HW. Our analysis also revealed temporal variations in the factors driving Korean and Chinese HWs due to typhoon passage and other multiple processes over heterogeneous surfaces (i.e., topographically induced Foehn winds, large-scale warm advection from the warm ocean, spatial differences in soil moisture). Our findings suggest that future heatwave-related studies should consider interactive contributions of key factors, their interplay with surface heterogeneities of complex terrain.