Estimation of gully erosion rate and its determinants in a granite area of southeast China.

• Soil erosion modulus of the large-scale gullies increased from north to south. • Hydraulic erosion dominated gully development during one-year monitoring period. • Contribution of gravity erosion to the gully was ascribed to hypsometric integral. • Clay in colluvial deposits contributed to regional difference of gully erosion. Gully erosion is the most serious threat to sustainable development of global ecosystem and economy, with declining soil productivity and fertility threatening agricultural production. However, due to limitations in quantifying gully erosion rate, origin of erosion could be hardly distinguished. This study aimed to figure out this problem by developing a soil erosion estimation method based on unmanned aerial vehicles (UAV) monitoring techniques. Specifically, 18 gullies with different terrain characteristics were selected across typical erosion regions in southeast China, and UAV low-altitude photography, weather station monitoring, and field sampling investigation were conducted from 2020 to 2021to monitor their total erosion volume (VE), collapse volume (VC), proportion of collapse volume to total erosion volume (VC%), morphological parameters (e.g., total length of scour channels, L; erosion area, A; residual volume, V; and hypsometric integral) and soil-environmental factors (rainfall, temperature, and soil properties). It showed that 92.65 % of VE was resulted from colluvial deposits, attributing to the variation of L. Additionally, VC quantifying the amount of gravity erosion was determined by soil clay content in the upper catchment (Clay1). And percentage of VC to VE, characterized by VC%, possessed a significant linear correlation with HI (R2 = 0.571, p < 0.001). Moreover, regional differences of VE and VC was mainly attributed to soil clay content in colluvial deposits (Clay3) and HI. Collectively, clay content in the gully system inhibited gully erosion, while all the morphologic factors facilitated the development of gully erosion. Meanwhile, rainfall and temperature had significant impacts on VE and the regional difference of VC, probably due to the limited monitoring period. [ABSTRACT FROM AUTHOR]