Background After the establishment of Qilian Mountain National Park, based on the Universal Soil Loss Equation (USLE) model, the soil water erosion in Qilian Mountain National Park in 2005, 2010 and 2015 was calculated and analyzed in order to show the spatio-temporal change of soil water erosion in the area.

Methods Based on the ULSE model, calculation method for each factor was selected according to the regional characteristics. The interpolation methods of precipitation erosivity factors were compared by choosing the method with the lowest MRE (mean relative error) when simulating rainfall amount. The R factor calculation method was selected through comparing the winter temperature in study area. And the L and S factors were obtained through calculation based on DEM. The MODIS (Moderate Resolution Imaging Spectroradiometer) vegetation index were extracted and calculated by ArcGIS and ENVI. The Chinese soil type data was used to assign values to different types of soil and the K factor was obtained. The land use information and slope data were used to calculate the P factor. R, LS, K, P, and C factors were multiplied to obtain the soil water erosion distribution of each year and the average. The zonal analyze tool of ArcGIS was used and the soil erosion at varies of elevations and slopes was analyzed.

Results The soil erosion modulus of Qilian Mountain National Park was 1 257.82 t/(km²·a) in 2005, 1 094.20 t/(km²·a) in 2010, 1 146.53 t/(km²·a) in 2015. The amount of soil erosion in each year has decreased from 6 134.26×10⁴ t/a in 2005 to 5 755.59×10⁴ t/a in 2015. The correlation of soil erosion modulus and R showed the soil water erosion was determined by not one but all the factors. And 70% of the study area was at low-level of erosion. The area with higher level of erosion was smaller. Soil erosion mainly occurred in area higher than or equal to 3 600 m and less than 4 600 m and the gentle slope greater than or equal to 8° and less than 15°. The area with elevation higher than or equal to 4 600 m contributed 25.67% of the amount of erosion.

Conclusions The soil water erosion of Qilian Mountain National Park shows that the overall amount of erosion are going down, the soil erosion status is improved. And the total erosion levels in all the three years are low and with a tendency of going lower. During the future process of development and prevention of soil erosion, the environment of gentle-slope-area with elevation between 3 600 m to 4 600 m of Qilian Mountain National Park should be well protected. And because the area higher than 4 600 m was with extremely high erosion modulus, as the glacier and permanent snow-cover may shrink, more bare land may expose to have risk of more soil erosion, demanding attention to prevent the environment damage of these areas.