黄土丘陵小流域土地利用变化对水土流失的影响

在土壤侵蚀模型LISEM (Limburg Soil Erosion Model) 校正的基础上,模拟了陕北黄土丘陵沟壑区大南沟小流域5种土地利用方案的水土流失效应,旨在探讨土地利用变化对流域出口水土流失的影响。研究结果表明:流域出口的洪峰流速、径流总量和侵蚀总量的大小顺序为:1975年>1998年>25度退耕>20度退耕>15度退耕。1975年和1998年25度以上的陡坡耕地和休闲地均退耕还林还草,这2种土地利用格局的径流和侵蚀模拟值都显著大于3种退耕方案。在3种退耕方案中,20度和15度以上的陡坡耕地和休闲地逐步转变为果园/经济林地,3种退耕方案之间的水土流失差异不显著。相对于1975年土地利用来说,1998年土地利用能降低洪峰流速、径流量和侵蚀量约5%~10%;3种退耕方案的减流减沙效益更加显著,可以降低洪峰流速、径流量和侵蚀量约40%~50%。

Effect Simulations of Land Use Change on the Runoff and Erosion for a Gully Catchment of the Loess Plateau, China

Based on the calibration of LISEM (Limburg Soil Erosion Model), five land use scenarios consisting of the previous in 1975 (LU75), present in 1998 (LU98) and future land use pattern were used to simulate the effects of the land use change on runoff and erosion at outlet of the Da Nangou catchment on the Loess Plateau, China. The future land-use maps were made based on three land-use scenarios in which cropland areas are restricted to slope gradients smaller than 25 (FA25), 20 (FA20) and 15 degrees (FA15). Two stages were recognized based on the comparison analysis on these five maps. In the first stage from LU75, LU98 to FA25, the area of the wood/shrub land increases while those of the wasteland, fallow land and cropland decrease, and the orchard/cash-tree land remains the same. During the second stage consisting of the FA25, FA20 and FA15, there is a gradual decrease in the cropland and fallow land and a gradual increase in the orchard/cash-tree land; the other land-use types remain the same. According to the simulation, the predicted peak-velocity, runoff and erosion at outlet decrease significantly if the slope cropland and fallow land are replaced by other types of land use. The peak-velocity, runoff and erosion show the same sequences for different land use patterns in the following order: land use in 1975 (LU75) > land use in 1998 > 25-degree-limit scenario > 20-degree-limit scenario > 15-degree-limit scenario. The runoff and erosion for LU75 and LU98 with much more cropland and fallow land is significantly greater than that for the three degree-limit scenarios with sharp increases in area of wood/shrub land. However, there is little difference in runoff and erosion among the three degree-limit scenarios since there is only a gradual decrease in the cropland and fallow land and a gradual increase in the orchard/cash-tree land. Based on the comparison with the land use in 1975, the predicted peak-velocity, runoff and erosion decrease by about 5-10% for land use in 1998, while the predicted decreases for the three slope-degree-limit scenarios are much larger, ranging between 40% and 50%.