Abrupt vapor pressure deficit changes over Northeast Asia during 1990s linked to combined Mediterranean-Pacific SST shifts

Vapor pressure deficit (VPD) is a crucial indicator of atmospheric dryness and humidity, influencing the land-atmosphere water exchange process. However, the mechanisms underlying VPD decadal abrupt change (DAC) and their impacts remain unclear. Here, we investigate the DACs of summer VPD in Northeast Asia during the late 20th century and explore the driving mechanisms. Our analysis reveals a significant increase of 20–30 % in summer VPD around 1998. Random forest modeling identifies surface temperature as the primary contributor, driven by atmospheric circulation shifts altering radiation patterns. The DAC of summer VPD in Northeast Asia coincided with abrupt sea surface temperature (SST) changes in both the tropical central Pacific and the Mediterranean Sea. AGCM simulations shed light on the underlying mechanisms driving the increasing DAC of summer VPD in Northeast Asia. These analyses reveal that a rapid decline in tropical central Pacific SST weakened the westerly jet stream. This weakening, in turn, led to a latitudinally uniform distribution of geopotential height and wind fields, ultimately triggering the formation of a high-pressure system over Northeast Asia. Additionally, a potential wave-like teleconnection pattern from the rapidly warming Mediterranean Sea may have further intensified this high-pressure system, exacerbating atmospheric dryness in the region. These findings highlight the role of synergistic SST anomalies in different regions driving atmospheric circulation changes, ultimately impacting regional VPD and dryness in Northeast Asia.