Dangerous degree forecast of soil and water loss on highway slopes in 1 mountainous areas using the revised universal soil and water loss 2 equation 3

13 Many high and steep slopes are formed by special topographic and geomorphic types and 14 mining activities during the construction of mountain expressways. Severe soil erosion may also 15 occur under heavy rainfall conditions. Therefore, predicting soil loss on highway slopes is 16 important in protecting infrastructure and human life. In this study, we investigate Xinhe 17 Expressway located at the southern edge of the Yunnan–Guizhou Plateau. The revised universal 18 soil loss equation is used as the prediction model for soil and water loss on slopes. Geographic 19 information systems, remote sensing technology, field surveys, runoff plot observation testing, 20 cluster analysis and co-kriging calculations are also utilised. The partition of the prediction units 21 of soil loss on the expressway slope in the mountainous area and the spatial distribution of rainfall 22 on a linear highway are studied. Given the particularity of the expressway slope in the 23 mountainous area, the model parameter is modified, and the risk of soil loss along the mountain 24 expressway is simulated and predicted under 20and 1-year rainfall return periods. The following 25 results are obtained. (1) Natural watersheds can be considered for the prediction of slope soil 26 erosion to represent the actual situation of soil loss on each slope. Then, the spatial location of the 27 soil erosion unit can be determined. (2) Analysis of actual observation data shows that the overall 28 average absolute error of the monitoring area is 33.24 t·km·a, the overall average relative error 29 is 33.96% and the overall root mean square error is between 20.95 and 65.64, all of which are 30 within acceptable limits. The Nash efficiency coefficient is 0.67, indicating that the prediction 31 accuracy of the model satisfies the requirements. (3) Under the 1-year rainfall return period 32 condition, we find through risk classification that the percentage of prediction units with no risk of 33 erosion is 78%. The soil erosion risk is low and does not affect road traffic safety. Under the 2034 year return period rainfall condition, the percentage of units with high and extremely high risks is 35 7.11%. The prediction results can help adjust the design of water and soil conservation measures 36 for these units. 37