黄土耕作坡面微地形面积高程积分计算及特征研究

面积高程积分(Hypsometric Integral,HI)是定量表征地形发育阶段及侵蚀趋势的重要指标。通过90mm/h雨强下4个典型坡度的人工模拟分段降雨试验,在三维激光扫描的基础上,利用点云数据生成DEM,对微地形坡面HI值的3种计算方法及其变化特征进行了分析,并根据细沟河网格网的HI值进行了验证。结果表明:1)HI方法可用于微地形坡面侵蚀发育的定量表征,HI值介于0.50-0.59之间。在不同坡度条件下,细沟出现之前坡面侵蚀量逐渐增加且HI总体呈现递减趋势,而细沟出现后侵蚀量在细沟中有所堆积且HI值有一定回增。2)河网格网HI值介于0.45±0.11之间。随着坡度的增加,HI值总体上表现出增加的趋势,潜在侵蚀能力有增大的趋势且侵蚀量和坡度之间存在一定的转折关系。3)对比3种不同HI计算精度来看,坡面HI与格网HI之间的RMSE和SAE值差别并不明显,但总体均表现为积分曲线法的计算精度要略优于体积比例法和起伏比法。研究结果对于丰富微地形尺度下HI的计算,深入认识坡面侵蚀发育过程及其机理具有重要的参考价值。

Calculation and characteristics of hypsometric integral to loess tilled slope on microtopographic scale

Hypsometric integral(HI)is an important geomorphological parameter for quantifying stages of landscape evolution and erosion status.In this study,artificial simulated segmented rainfall experiments with four typical slope gradients under rainfall intensity(90 mm/h)were conducted.Based on three-dimensional laser scanning,DEM was generated by using point cloud data,and the calculation methods for slope HI value at different stages of erosion development and the change characteristics were analyzed,and the calculation methods were verified based on the HI values of the rill river grids.The results show that:1)The HI values of the erosional slope range between 0.50 and 0.59,which indicates that HI is able to quantify the stage of the surface evolution and erosion status.Under different slope conditions,the amount of erosion gradually increases and the HI value tends to decrease on the whole before rills emerges,while after the emergence of rills,eroded mass accumulates in the rill network and the HI value curves up considerably.2)The HI values based on river network grid range between 0.34 and 0.56.With the increase of slope,they tend to increase on the whole;the potential erosion tends to grow,and the amount of erosion is in inverse proportion to slope.3)Root Mean Squared Error(RMSE)and Sum of Absolute Errors(SAE)for three different HI calculation accuracy show no clear differences.However,the trend shows that RMSE and SAE are smallest when HI values are calculated by using integral curve,followed by elevation to relief ratio and volume to volume ratio,which indicates calculation by using integral curve contributes to a better precision.The results of this study have important reference for enriching HI calculation at microtopographic scale and further understanding the slope erosion development process and its mechanism.