Abstract:

The vegetation optical depth （VOD）， as a crucial indicator reflecting surface biomass and vegetation water content， plays a vital role in accurately characterizing the changes in VOD under the context of large-scale vegetation restoration on the Loess Plateau. This is crucial for scientifically assessing the benefits of ecological engineering. This study， using X-band VODCA data， employs various methods including trend analysis， partial correlation analysis， and residual analysis to scrutinize the spatiotemporal variations of vegetation optical depth （VOD） on the Loess Plateau from 2003 to 2018. The research quantifies the respective contributions of climatic factors and human activities to the fluctuations in vegetation optical depth. The result indicates that： （1） The VOD on the Loess Plateau showed a significant increasing trend during the period of 2003-2018， with a growth rate of 0.28%/10a （P<0.01）. Moreover， the growth rate in autumn surpassed that in spring and summer， reaching 0.32% /10a （P<0.01）. （2） In terms of spatial distribution， there was a significantly increasing trend in VOD across 69.7% of the Loess Plateau， while the VOD decrease was observed in only 5.4% of the area， primarily concentrated in the northern part of Inner Mongolia and western Ordos. （3） In the Loess Plateau， the VOD showed a significant positive correlation with precipitation and solar radiation， mainly distributed in the western semi-arid grassland region. Conversely， negatively correlated regions were predominantly distributed in the gully areas in the southern part of Gansu Province. （4） Regression analysis reveals that the relative contributions of temperature， precipitation， radiation， and human activities to VOD are 45.74%， 2.09%， 38.20%， and 13.97%， respectively. Notably， the impact of human activities is progressively growing， encompassing 88.4% of the study area with an increasing trend. The comprehensive results of this study reveal the dynamic features of VOD changes on the Loess Plateau， offering a scientific basis for estimating vegetation carbon storage and supporting sustainable management in the context of ecological restoration on the Loess Plateau.

Key words: vegetation optical depth, ecological restoration, spatiotemporal variation, influencing factors, Loess Plateau