Identifying precipitation gradients and revegetation ages combined effects deep soil moisture variability in the typical loess region

A Typical Loess Region (TLR) in the Chinese Loess Plateau Water scarcity is the primary constraint on ecological sustainability in the Typical Loess Region (TLR), where large-scale revegetation efforts have been implemented to combat severe soil erosion. However, the sustainability of these restored ecosystems is highly uncertain. This is because the water consumption of introduced vegetation often exceeds precipitation input, leading to progressive depletion of deep soil moisture (DSM) that supports plant survival during drought. While both spatial precipitation gradients and temporal revegetation age are known to influence DSM independently, their synergistic effects on DSM variability remain poorly quantified. Thus, to assess regional influences on DSM variability, we assembled 81 DSM profiles extending to depths of 10 m in TLR, spanning revegetation ages from 0 to 40 years. A polynomial function framework coupled with error propagation analysis was used to assess the combined effects. The results reveal that soil moisture and water storage generally increase with depth in shallow-rooted systems, reaching maximum levels at 5–10 m. However, under deep-rooted plants, they are highest at depths of 5–10 m, intermediate in 0–2 m, and the lowest in 2–5 m. With prolonged revegetation, soil moisture deficits intensify progressively across all soil layers, especially within the active and stable layers. Soil moisture conditions exhibit pronounced spatial heterogeneity, with mean moisture content and storage revealing increase gradient from northwest to southeast of the TLR. A transition from sufficient to stressed DSM conditions occurs when annual rainfall falls between 381.4 ± 130.5 and 450.5 ± 171.6 mm year −1 , triggered by a critical revegetation age of 25.7 ± 3.6 years. These findings highlight the need to integrate such thresholds into water resource management and ecosystem restoration strategies, especially in water-scarce and degraded regions. • Database of 81 DSW profiles to 10 m deep with ages up to 40 years was compiled. • SWCD getting severe in different soil layers under the revegetation ages increasing. • Spatial variability of DSW coincides with that of precipitation gradients. • Optimal value of revegetation age and precipitation does exist and be identified.