Estimation of sediments produced in a subbasin using the Normalized Difference Vegetation Index

ABSTRACT Among the parameters considered by the Revised Universal Soil Loss Equation (RUSLE), the soil cover and management factor (C) is the main human influenced factor affecting the estimation of water erosion, and one of the most sensitive to spatiotemporal variations. Consequently, this study aims to compare the efficiency of C factor estimates obtained from the literature for each land-use class (Clit) and by calculation based on the Normalized Difference Vegetation Index (CNDVI). We test the hypothesis that soil loss estimates based on CNDVI approach are more accurate than those based on Clit. Water erosion was estimated based on soil morphological, physical, and chemical properties in addition to climate, relief, management practices, and land use and cover. The modeling steps were realized with the help of the Geographic Information System. The results were validated using the data of total sediment transported with water discharge and daily runoff. RUSLE underestimated soil losses by 0.64 Mg ha-1 year-1 using Clit and 0.45 Mg ha-1 year-1 with CNDVI, which corresponds to errors of 21.05% and 14.80%, respectively. Therefore, the CNDVI factor results are more accurate. Both methodologies identified areas with high erosion rates where the adoption of mitigation measures should be prioritized.

摘要：在修正通用土壤流失方程（RUSLE）所考量的各项参数中，土壤覆盖与管理因子（C因子）是影响水蚀估算的主要人为影响因子，同时也是对时空变化最为敏感的参数之一。因此，本研究旨在对比两种途径得到的C因子估算值的效能：一种是基于已有文献针对各土地利用类型（Clit）得到的C因子估算值，另一种是基于归一化植被指数（CNDVI）计算得到的C因子估算值。本研究验证的假说为：基于CNDVI方法得到的土壤流失估算结果，要比基于Clit得到的结果更为精准。本次水蚀估算综合考量了土壤的形态、物理及化学特性，同时纳入了气候、地形、管理措施以及土地利用与覆被数据。本次建模流程借助地理信息系统（Geographic Information System）完成。研究结果通过日径流量与输沙总量的实测数据进行了验证。采用Clit方法时，RUSLE对土壤流失量的估算值偏低0.64 吨·公顷⁻¹·年⁻¹；采用CNDVI方法时则偏低0.45 吨·公顷⁻¹·年⁻¹，对应的相对误差分别为21.05%与14.80%。由此可见，基于CNDVI的C因子估算结果精度更高。两种方法均识别出了侵蚀速率较高的区域，此类区域应优先实施侵蚀减缓措施。