Soil erosion on highway side-slope has been recognized as a cause of environmental damage and a potential threat to road embankments in the high-altitude permafrost regions. To assess the risk to roads and to protect them effectively, it is crucial to clarify the mechanisms governing roadside erosion. However, the cold climate and extremely vulnerable environment under permafrost conditions may result in a unique process of roadside erosion, which differs from the results of current studies conducted at lower altitudes. In this study, a field survey was conducted to investigate side-slope rill erosion along the permafrost of a highway on the Qinghai-Tibet Plateau of China. Variations in erosion rates have been revealed, and intense erosion risks (with an average erosion rate of 13.05 kg/m2/a) have been identified on the northern side of the Tanggula Mountains. In the case of individual rills, the detailed rill morphology data indicate that the rill heads are generally close to the slope top and that erosion predominantly occurs in the upper parts of highway slopes, as they are affected by road surface runoff. In the road segment scale, the Pearson correlation and principal component analysis results revealed that the protective effect of vegetation, which was influenced by precipitation, was greater than the erosive effect of precipitation on roadside erosion. A random forest model was then adopted to quantify the importance of influencing factors, and the slope gradient was identified as the most significant factor, with a value of 0.474. Accordingly, the integrated slope and slope length index (L0.5S2) proved to be a reliable predictor, and a comprehensive model was built for highway side-slope rill erosion prediction (model efficiency = 0.802). These results could be helpful for highway side-slope conservation and ecological risk prediction in alpine permafrost areas.

Erosion is an ongoing environmental problem that leads to soil loss and damages ecosystems downstream of agriculture. Increasingly frequent heavy precipitation causes single erosion events with potentially high erosion rates owing to gully erosion. In this study, analyses of croplands affected by heavy precipitation and linear erosion indicate that erosion occurs only on sparsely vegetated fields with land cover <= 25% and that slope gradient and length are significant factors for the occurrence of linear erosion tracks. Existing erosion models are not calibrated to the conditions of heavy precipitation and linear erosion, namely high precipitation intensities and long and steep croplands. In this study, natural linear erosion was analyzed using an unmanned aerial vehicle and erosion volumes were determined for 32 rills and gullies of different sizes. Comparisons with the RUSLE2 and EROSION-3D model values showed an underestimation of linear erosion in both models. Therefore, calibration data for erosion models used for heavy precipitation conditions must be adapted. The data obtained in this study meet the required criteria.