Waveguide Teleconnection Mechanisms Driving Summer Compound Heat-Humidity Extremes in China Land Monsoon Region

Abstract

Escalating compound heat-humidity extremes (CHHEs) pose severe threats to socioeconomic stability and human health. Using the wet-bulb globe temperature, we reveal summer CHHEs exhibited consistently increasing trends across the China Land Monsoon (CLM) region during 1961–2022, significantly in the northeast and southwest. The 13-year sliding correlations indicate that since 2000, the British Okhotsk Corridor (BOC)-Silk Road Pattern (SRP) nexus shifted from a strong to weak state, which influenced CHHEs variability. During the weak BOC-SRP nexus period, an anomalous high-pressure system dominated northern China, especially northeastern CLM, and was intensified by negative potential vorticity anomalies through subsidence and diabatic heating. Simultaneously, abundant moisture transport from the western Pacific into northeastern CLM reinforced hot and humid conditions, jointly increasing CHHEs. Over southwestern CLM, the high-pressure system strengthened anomalous easterlies, which together with negative vorticity advection increased moisture divergence. Additionally, meridional temperature advection promoted warm air accumulation in the lower troposphere, further increasing CHHEs. Finally, the weak BOC-SRP nexus is modulated by North Atlantic tripole sea surface temperature anomalies by Rossby wave energy divergence, as confirmed by Community Earth System Model simulations. Overall, this study highlights the critical role of mid- to high-latitude teleconnections variable coupling states in regulating CHHEs in the CLM region.