Asymmetric Responses of Summer Soil Moisture Anomalies to the Large-Scale Teleconnections on the Loess Plateau between 2000 and 2020

Soil moisture is a key regulator of hydrological cycle and is closely related to vegetation growth and climate changes. However, exactly how soil moisture content (SMC) anomalies on the Loess Plateau respond to large-scale teleconnection remails unclear. Here, based on 1 km daily soil moisture dataset using in situ measurement and machine learning, we demonstrated that there was an interdecadal fluctuation from 2000 to 2020 in the sensitive areas of vegetation restoration (SAVR) of the Loess Plateau, with only 13.3% of areas whose tendency passed a significant level of 0.05. Spatially, areas with summer SMC anomalies greater than 5 m3/m3 (less than -5 m3/m3) accounted for 28.1% (15.4%) in positive (negative) anomalous years, and this discrepancy can be attributed to distinct circulation pattern and anomalous water vapor transport. We found that there was the asymmetrical distribution of the large-scale atmospheric patterns between positive and negative anomalous years. In positive anomalous years of summer SMC, combination between anomalous low-pressure system around the Lake Baikal and westward expansion of western Pacific subtropical high triggered sustained southerly on the west flank, and strengthened meridional water vapor transport from south China and western north Pacific to North China. However, during negative anomalous years of summer SMC, an anomalous anticyclone prevailed over the western north Pacific transported moisture northwestward to central-eastern China rather than the Loess Plateau. Under above of the large-scale atmospheric patterns, water vapor accumulation was approximately 4.1-fold more abundant in the positive anomalous years of summer SMC than in negative anomalous years, corresponding to anomalous upward and sinking motions, further leading to more and less SMC in summer, respectively. The conclusions of this study have implications for excavating early warning information of SMC anomalies and natural restoration sustainable management on the Loess Plateau.