Spatio-temporal variations in soil erosion and its influence factors in Taihang Mountain area based on RUSLE modeling

The study of soil erosion characteristics and their spatial heterogeneity is of great significance for ecological environmental protection. Soil and water conservation is important in Taihang Mountain area. This study was conducted to explore these characteristics. Supported by the normalized difference vegetation index (NDVI), digital elevation model (DEM), and land use data combined with geographic information system (GIS) and remote sensing (RS) technologies, the soil erosion modulus in Taihang Mountain area was calculated from 2000 to 2015 based on the revised universal soil loss equation (RUSLE) model. The spatiotemporal variation in soil erosion in the study area was analyzed, and the relationship between soil erosion, slope gradient, land use type, and NDVI was explored. The results showed that: 1) The average soil erosion modulus were 4434.14 t∙km⁻²∙a⁻¹, 2984.65 t∙km⁻²∙a⁻¹, 1761.93 t∙km⁻²∙a⁻¹ and 1833.81 t∙km⁻²∙a⁻¹ in 2000, 2005, 2010 and 2015, respectively. The erosion modulus showed a notably decreasing trend from 2000 to 2015 with a decreasing rate of 58.64%. 2) The areas where erosion intensity decreased by one level were always larger than those where it increased by one level. However, erosion intensity did not change in more than 74.77% of the total area. The maximum reduction in the erosion intensity occurred in the period of 2005–2010. 3) From 2000 to 2005, the decline in erosion intensity level in Taihang Mountain area was mainly distributed in higher elevation regions near the border of the Shanxi and Hebei Provinces. The areas with decreasing soil erosion intensity from 2005 to 2010 were uniformly distributed in the study area and were mainly located in the south of Yangquan and Shijiazhuang from 2010 to 2015. 4) In 2015, 86.54% of the total soil erosion (2.5×10⁸ t) was concentrated in the mid-mountain and hilly zones, where accounted for approximately 91.12% of the study area. There was no obvious correlation between the erosion modulus and altitude in this area, whereas it showed a positive relationship in the subalpine zone. 5) The erosion modulus had a positive correlation with slope gradient; the threshold value was 40º, and the erosion modulus reached a maximum value of 4693 t∙km⁻²∙a⁻¹. With an increase in slope gradient, the possibility of soil erosion increased gradually with higher grades of erosion intensity. Cultivated land, forest land and grassland were the three main land use types in the study area, and their average soil erosion modulus were 501.72 t∙km⁻²∙a⁻¹, 2475.46 t∙km⁻²∙a⁻¹ and 3505.73 t∙km⁻²∙a⁻¹, respectively. The average slope gradient of the cultivated land was 4.90º, which resulted in the minimum soil erosion modulus. Grassland was the land use type with the largest erosion modulus. The soil erosion modulus decreased significantly with an increase in annual NDVI, and the rate gradually slowed down when NDVI reached 0.66. Soil erosion is a significant index for eco-environmental quality appraisal. This study provides a scientific basis for soil erosion control and ecological engineering measures in Taihang Mountain area.