Quantifying spatiotemporal variations in soil moisture driven by vegetation restoration on the Loess Plateau of China

Abstract

Characterizing soil moisture (SM) dynamics is a prerequisite for implementing sustainable vegetation restoration on the Loess Plateau (LP) of China. However, quantifying SM variation both spatially and temporally remains a challenge due to various driving factors and the complexity of land surface processes. This study was designed to investigate the magnitude and trends of SM variation due to vegetation restoration in soil profiles at the regional scale using earth system reanalysis data and the Community Land Model (CLM). The results indicated that the surface layer SM had positive responses to vegetation restoration, while the SM in the subsurface and deeper soil layers had negative responses. The area-averaged annual mean SM under vegetated condition in 2015 (LC2015) was less than that in 2000 (LC2000), with a magnitude of 11.7 mm. Spatially, almost the whole LP region exhibited decreased SM in the 100–289 cm layer in the LC2015 simulation, and significant differences were detected on the southeastern LP, where the forest coverage clearly increased from 2000 to 2015, with the decreased annual mean SM ranging from 20 to 40 mm. These differences were also reflected in the seasonal SM, showing that SM in the 100–289 cm layer in the LC2015 simulation was less than that in the LC2000 simulation, with significant differences of 11.5 mm, 11.7 mm, 11.9 mm and 11.7 mm for spring, summer, autumn and winter, respectively (p < 0.05). Notably, the temporal variabilities in SM in both the LC2000 and LC2015 simulations showed a decreasing trend during the simulation period, and the decreasing magnitudes increased as the soil depth increased; the largest decreasing gradient was approximately 2.1 mm/year in the 100–289 cm layer. These findings implied that vegetation restoration on the LP led to a significant reduction in SM, that was difficult to replenish by local precipitation and in turn had negative effects on plant growth and water resources.