区域土壤侵蚀定量评价中的坡长因子尺度变换方法

Re-scaling method of slope length factor in the soil erosion assessment of regional scale

区域土壤侵蚀研究中,坡度、坡长只能基于中低分辨率DEM提取,但提取的坡度发生衰减,坡长发生扩张。以陕西省延安市及周边地区为研究区,利用国家测绘局生产的1∶25万数字地形图和研究区内典型地区1∶5万数字地形图,在ANUDEM软件支持下,建立了研究区50 m分辨率和典型地区10 m分辨率的水文地貌关系正确DEM,利用直方图匹配原理对50 m分辨率DEM上提取的坡度、坡长进行变换,并对变换前后坡度、坡长对土壤侵蚀强度的影响进行了评价分析。结果表明,经变换后的坡度整体变陡,坡长整体变短,变换后坡长平均值和累积频率曲线与高分辨率(10 m)坡长均较接近,且其空间格局基本保持不变。利用中国土壤流失方程计算坡度坡长均不变换、只对坡度变换、只对坡长变换和坡度坡长均变换4种情况下的土壤侵蚀强度研究结果表明,只对坡长变换时土壤侵蚀强度有所减小,而只对坡度变换和坡度、坡长均变换时土壤侵蚀强度增大,且前者增大幅度较大。说明坡度衰减比坡长扩张对土壤侵蚀评价结果的影响更大,在实际应用中有必要对坡度和坡长都进行变换,以期为土壤侵蚀定量评价提供更加准确的数据支持。

It＇s the only way to extract slope and slope length based on low resolution DEMs for the studies of regional scale soil erosion modeling.But the slope will reduce and the slope length will enlarge.Based on the hydrologically correct DEM of 50 m and 10 m resolution using AUNDEM software in Yan＇an and its surrounding areas of Shaanxi Province with the 1∶250 000 digital topographic maps and the typical area of this areas with the 1∶50 000 digital topographic maps,the derived slope and slope length from 50 m resolution DEM were re-scaled to similar to the slope and slope length from 10 m resolution DEM using histogram matching principle.Then the effects of the slope and slope length of pre and post of re-scaling on soil erosion intensity was evaluated and analyzed.Results show that re-scaled slope gradient becomes steep and the re-scaled slope length becomes short with similar histograms to high resolution＇s slope length when this method can promises space structure steadiness.Meanwhile,four datasets of soil erosion intensity are calculated with Chinese Soil Loss Equation（CSLE）,including（a） slope and slope length unre-scaling,（b）slope re-scaling,（c）slope length re-scaling,（d）slope and slope length re-scaling.Results show that the（a） can obviously increase soil erosion intensity,the（b） can decrease soil erosion intensity,but the（c） can finally increase soil erosion intensity,which can provide more accurate data support for the soil erosion assessment.