陕北无定河流域土壤侵蚀时空演变

摘要

为了深入认识陕北无定河流域土壤侵蚀时空演变过程及其与降雨和植被NDVI变化的关系,采用基于RUSLE(修正通用土壤流失方程)的土壤侵蚀评估方法,开展流域土壤侵蚀时空分布及其与降雨、植被NDVI的关系研究.结果表明:①2000-2014年无定河流域多年均土壤侵蚀模数为457.90 t/(km2·a),呈波动增加过程.流域土壤侵蚀以微度侵蚀为主,占流域总面积的88.35％,其他土壤侵蚀等级面积比例随等级升高而减少.研究时段内除微度侵蚀面积比例减少外,其他土壤侵蚀等级面积比例均呈增加过程,并且侵蚀面积年变化速率也由微度侵蚀的0.52％降至剧烈侵蚀的0.01％.②无定河流域西北部土壤侵蚀程度最低,西南部其次,东南部最高,与其地貌类型及降水量沿东南—西北方向递减有关,但均反映出流域2000-2014年土壤侵蚀的增加过程.研究时段内流域不同土壤侵蚀等级间面积及比例转移主要由低等级土壤侵蚀类型转为相邻高等级土壤侵蚀类型.③无定河流域土壤侵蚀与降水量、侵蚀性降雨量、降雨侵蚀力呈显著正相关(P＜0.01),相关系数分别为0.90、0.95和0.98,而与植被NDVI的关系不显著.研究显示,降雨变化尤其是侵蚀性降雨(≥12 mrn/d)增加是陕北无定河流域土壤侵蚀增强的主要原因.%Based on the Revised Universal Soil Loss Equation (RUSLE),the temporal and spatial evolution of soil erosion and possible relationship with rainfall and NDVI were investigated for the Wuding River Basin in northern Shaanxi province.The results showed that:(1) The average annual soil erosion in the Wuding River Basin modulated around 457.90 t/(km2 · a),and showed an increase in volatility.The main soil erosion type was slight erosion,accounting for 88.35％,while the area of other soil erosion type decreased as the soil erosion level increased.In addition to the decrease in area and proportion of slight erosion,the other soil erosion type increased,and the change rate also decreased from 0.51％ each year for the slight soil erosion type to 0.01％ each year for severe erosion.(2) In order to clearly show the status of soil erosion in different regions,three small areas in the southeast,southwest,and northwest of the Wuding River Basin were selected.Soil erosion modulation was the highest in the southeast area,followed by the southwest area,and the northern area in the Wuding River Basin was the lowest.The distribution of soil erosion modulation was related to landforms and decreased rainfall from the southeast to the northwest,which reflected the increased process of soil erosion in the Wuding River Basin from 2000 to 2014.(3) The correlations between soil erosion modulation and rainfall,erosive rainfall,and rainfall erosivity were significantly positive,with respective correlation coefficients 0.90,0.95 and 0.98,but the correlation between soil erosion and NDVI was not significant.Thus,changes of rainfall,especially the increase of erosive rainfall (≥＞ 12 mm/d),were the main reason for the enhanced soil erosion of the Wuding River Basin.