Ii ) runoff erosivity reflects relationship of water erosion forces and sediment yield more directly than rainfall erosivity . it intergrated ability of runoff volume and flood peak on detaching soil and transporting sediment and is more reasonable than single runoff depth or flood peak volume ( 2 )以径流侵蚀力代替降雨侵蚀力来反映水蚀营力与产沙量的关系更加直接,而且综合了径流量与洪峰在剥蚀土壤和搬运泥沙能力,比单独运用径流深或洪峰流量更加合理。