Identifying the short-duration and long-duration types of summer soil moisture drought on the Loess plateau and their teleconnections

Soil moisture drought poses a destructive effect on vegetation growth and water resource. Modeling event-based drought processes could serve as a pathway for better understanding how different types of soil moisture drought responds to larger-scale teleconnections in the monsoon and loess critical zone of China. Based on the daily soil moisture dataset named SMCI1.0 at top 1 m, we found that the Loess Plateau witnessed an aggravated summer soil moisture drought, with summer standardized soil moisture index (SSMI) decreasing by 1.5 % year⁻¹ from 2000 to 2020. According to the durations and spatial coverage of events, we classified 12 summer soil moisture drought events occurring on the Loess Plateau into short-duration (6–14 days) and long-duration (≥15 days) types, and further discussed their different large-scale teleconnections. Interestingly, we found the short-duration (long-duration) summer soil moisture drought was influenced by wave train (blocking) circulation anomalies. The short-duration summer soil moisture drought broke out with an eastward “− + − +” wave train over Eurasia, which was mainly attributed to a tripolar sea surface temperature (SST) mode over the North Atlantic and weakened South Asian high (SAH) with westward shift. Such a structure resulted in water vapor deficit of Loess Plateau, and thus favored shorter summer soil moisture drought on the Loess Plateau. For the long-duration summer soil moisture drought, consistently warm tropical Atlantic and North Sea-Baltic Sea favored the “+ − +” wave train, weaking the southward movement of cold air and maintaining prolonged water vapor deficit accompanied by downward prevails, which consequently provided a favorable condition for more long-lasting and enhanced summer soil moisture deficit. Insights into the large-scale teleconnections related to the different types of soil moisture drought event not only can provide drought early warning information, but also offer a scientific guidance for revegetation projects on the Loess Plateau or other Eurasian drylands.