The Important Role of Reduced Moisture Supplies from Monsoon Region in the Formation of Spring and Summer Droughts over Northeast China

Abstract

Abstract Anomalies in atmospheric moisture transport are critical for drought formation, with East Asian monsoon anomalies identified as the primary driver of droughts in East Asia. However, the drought mechanism for the border region between monsoon and non-monsoon land areas remains unclear due to complex interactions between latitudinal circulation patterns. Using a Lagrangian framework, we quantify moisture supply (MS) during spring and summer drought events within the border region, specifically Northeast China (NEC). Our results reveal that decreased MS from monsoon land area is more crucial than non-monsoon land area and local area for NEC droughts, and the local water recycling playing a more substantial role in summer than in spring. On average, summer droughts are four times more intense than spring droughts. Contributions to MS deficits from monsoon land area, non-monsoon land area and local area during spring (summer) droughts are 43.2% (43.8%), 25.1% (19.2%), and 22% (33.8%), respectively. The weakened atmospheric circulation from source regions to NEC contributes to over 80% of MS deficits during droughts. Atmospheric wave trains triggered by North Atlantic sea surface temperature anomalies (SSTA) gradients, along with the weakening of the East Asian subtropical westerly jet in spring and a positive phase of polar-Eurasian teleconnection in summer, contribute to spring and summer droughts, respectively. A sustained, record-breaking positive SSTA along the Western European coast from spring to summer excited wave train, resulted in the extreme 2017 spring-summer drought. These findings provide valuable insights into the drought mechanism within the interaction zone of circulation systems from different latitudes.