Precipitation buffers gully erosion through vegetation cover across the Tibetan Plateau.

Abstract

Gully erosion is important trace left by soil erosion, and its density characteristics are regarded as a significant indicator of land degradation. The Tibetan Plateau, with little human influence, is an ideal site for studying the natural development of gullies. In this study, three indicators, namely gully number density (GND), gully length density (GLD) and gully area density (GAD), were used to investigate the spatial pattern of gully erosion on the Tibetan Plateau. The optimized XGboost algorithm and spatialized SHapley Additive exPlanations were employed to model three gully densities, and identifies the significance of driving factors along with the response relationships of gully density to these factors. The results reveal that arid regions in the northern Tibetan Plateau are high-value areas for gully density. Mean annual precipitation (MAP) dominates the gully density spatial pattern, followed by elevation and slope steepness. The two indicators of the cryosphere, namely, the permafrost thermal stability and the snow cover days, had the least impact on gully density. This indicates that gully erosion is dominated by precipitation rather than freeze-thaw. The inhibitory effect of MAP on gully erosion was observed, mainly through its role in promoting vegetation growth. Additionally, this study identified two key MAP thresholds of 150 mm and 400 mm, which play an important role in gully density. Specifically, in arid regions with MAP below 150 mm and in semi-humid to humid regions with MAP exceeding 400 mm, MAP emerges as the dominant factor. In contrast, within semi-arid areas (150 mm < MAP < 400 mm), the dominant influencing factors are more complex. Through quantitative assessment, this study reveals that gully erosion on the Tibetan Plateau is mainly driven by precipitation rather than freeze-thaw. Moreover, at a regional scale, precipitation suppresses gully erosion by promoting vegetation cover, rather than promotes gully erosion. These findings offer new insights for the gully erosion mechanism, provide an important perspective for research on the dominant drivers of soil erosion, and deliver guidance for soil and water conservation efforts on the Tibetan Plateau.