柔远川小流域土地利用强度变化对径流的影响

我国西北地区水资源短缺,近年来河川径流又大幅减少。气候变化和土地利用类型的变化都不是主因,推测可能是土地利用强度和植被结构发生改变引起的。为此,基于柔远川小流域2009年QuickBird遥感影像,结合流域DEM和坡位图,分析流域土地利用强度变化对径流的影响。结果表明:1)柔远川小流域土地利用以草地和农田为主,各占流域面积的69.8%和21.7%,森林仅占3.4%;2)森林主要为疏林,郁闭度、密度和冠幅平均为0.1、260株/hm2和3.4 m;3)草地除受自然因素的影响外还受人为活动的干扰,人为活动可分为苜蓿种植地、水平沟草地和鱼鳞坑草地,分别占流域面积的6.2%、4%和1.8%,但依然以天然草地为主,占流域面积的57.8%,草地以中覆盖度(20%～50%)草地为主,占流域面积的44.2%,高覆盖度(>50%)草地仅占流域面积的2.8%,且全部为苜蓿种植地;4)对坡耕地进行大规模的梯田改造,坡式梯田与水平梯田各占流域面积的6.5%和4.6%,而坡耕地占流域面积的9.3%。研究可知,在泾河流域,以农田梯田化和种植人工草地为主要特征的土地利用强度正在加大,这会对流域径流产生强烈的影响。

Effects of Land use change on runoff in Rouyuanchuan small basin

The annual runoff had decreased dramatically during last several decades in NW China.This led that the water shortage in this region was more serious.However,ongoing climate change and land use change（i.e.forestation and afforestation） were found not to be key reasons of this runoff reduction.Thus,it was speculated that land use intensity increasing and veqetation structure variation were the main reasons of this runoff reduction.In present paper,Rouyuanchuan,a small basin located in NE,was chosen as research area and its land use intensity was analyzed according to its image data recorded by QuickBird in 2009,and DEM.Results showed that： 1） In Rouyuanchan small basin,grassland and cropland were the key types of land use as 69.8% and 21.7% of basin area,respectively.But forests only accounted for 3.4% of basin area.2） Forest were open forest with average crown density of 0.1,average tree density of 260 trees/hm2,average canopy width of 3.4 m.3） Three types of artificial grassland,i.e.alfalfa plantation,grassland within ditches and grassland within small pits,occurred with 6.2%,4% and 1.8% of basin area,respectively;however,natural grassland was still key type of grassland which accounted for 57.8% of basin area.Grassland with medium level of coverage（20%-50%） accounted for 44.2% of basin area.Grassland with high level of coverage（＆gt;50%）,which was consisted of alfalfa plantation,amounted to only 2.8% of basin area.4） The landform was changed strongly by cropland terracing.Terraces,which accounted for 11.1% of basin area,were more than traditional sloping cropland in Rouyuanchuan small basin.These indicated that land use intensity was increasing and vegetation structure was changing e.g.terracing farmland and grass plantation,which would strongly affect on the runoff.