Spatial distribution and influencing factors of Surface Nibble Degree index in the severe gully erosion region of China’s Loess Plateau

Abstract

In China's Loess Plateau severe gully erosion (LPGE) region, the shoulder-line is the most intuitive and unique manifestation of the loess landform, which divides a landform into positive and negative terrains (PNTs). The spatial combination model of PNTs is of great significance for revealing the evolution of the loess landform. This study modeled and proposed the Surface Nibble Degree (SND), which is a new index that reflects the comparison of the areas of PNTs. Based on 5 m DEMs and matched high-resolution remote sensing images, the PNTs of 164 complete watersheds in the LPGE were extracted accurately, and the SND index was calculated. The spatial distribution trend of SND was discussed, and the relationship between SND and the factors that affect the evolution mechanism of regional landform was explored further. Results show that: (1) The SND can be calculated formally. It can quantify the development of the loess landform well. (2) The SND of the LPGE has evident spatial differentiation that increases from southwest to northeast. High values appear in Shenmu of Shaanxi, Shilou of Shanxi, and northern Yanhe River, whereas the low values are mainly distributed in the southern loess tableland and the inclined elongated ridge area of Pingliang in Gansu and Guyuan in Ningxia. (3) In the Wuding River and Yanhe River, the SND decreases with the increase in flow length (FL). In the North-Luohe River and Jinghe River, the SND increases with FL. (4) SND is significantly correlated with gully density and sediment modulus and moderately correlated with hypsometric integral. As for the mechanism factors analysis, the relationship between loess thickness and SND is not obvious, but SND increased first and then decreased with the increase of precipitation and vegetation in each geographical division, and we found that the land use type of low coverage grassland has greater erosion potential.

Large-Scale Spatial Variability in Loess Landforms and Their Evolution, Luohe River Basin, Chinese Loess Plateau

“…The prerequisite for applying the HI value is that the landform development is a completely closed system by default, and the evolution of the landform is entirely controlled by internal forces (Strahler, 1952). However, the development of loess landforms does not fully conform to this hypothesis, and its development is disturbed by various factors, including rainfall, land use, and anthropogenic activities (Wang et al, 2016;Zhou et al, 2021;). Some scholars have also developed other indicators to quantify the stage of landform development, such as entropy.…”

Integrating Topographic Skeleton into Deep Learning for Terrain Reconstruction from GDEM and Google Earth Image

“…Therefore, there is a certain conversion rule between the ridge and valley lines of different resolution DEMs. The gully line is the boundary line of gully erosion [41][42][43][44][45] and separates the water dispersion and convergence areas, distinguishing positive and negative landforms. To accurately convey the spatial location of the gully, it requires a higher-resolution DEM, but global open-source DEMs do not fulfill this requirement.…”