Expansion and intensification of deep soil drying on the Loess Plateau of China over the last three decades

Soil water is experiencing continuously changing under current land use change. The launch of the great “Grain for Green” (GFG) project expanded the revegetation area on the Loess Plateau of China, with the consumption of soil water resources, even in the deep soil. However, spatial and temporal changes of deep soil drying are lacking at a large scale due to observational constraints, and their development caused by revegetation has not been addressed. Here, we utilized dried soil layer (DSL) indices to evaluate the degree of deep soil drying based on a published soil water dataset for the 1–10 m soil profiles. We divided the study period into Period-1 (1985–1999) and Period-2 (2000–2015) with the start of the GFG project (1999) as the turning point, and obtained the annual spatio-temporal distribution of DSLs by using the spatial random forest method. DSL areas mainly extended from the arid and semi-arid regions in Period-1 to the semi-humid region in Period-2. The mean soil water content within the DSL (DSL-SWC) significantly decreased from 8.6% in Period-1 to 7.4% in Period-2. Enlarged and intensified DSLs across the Loess Plateau from Period-1 to Period-2 indicated that the degree of deep soil drying increased after the GFG project at the regional scale due to revegetation. To better support the greenness of revegetation, we proposed management practices incorporating large-scale revegetation allocation and small-scale management reinforcement for sustainable ecosystem development.