1995-2018年石羊河流域下游荒漠化动态变化

Dynamics of desertification in the lower reaches of Shiyang River Basin,Northwest China during 1995-2018

以石羊河流域下游甘肃省民勤县为研究区,选取1995、2000、2005、2010、2015、2018年6期遥感影像作为数据源,利用RS和GIS理论和方法,基于归一化植被指数(NDVI)和地表反照率(Albedo)建立Albedo-NDVI特征空间,构建荒漠化差值指数,对民勤县荒漠化动态变化进行分析。结果表明:石羊河流域下游地区荒漠化面积占民勤县总面积的90%以上,绿洲零星分布在大面积荒漠化土地中,以中度荒漠化为主,占全县总面积的70%以上;1995—2018年间,民勤县荒漠化面积整体呈减少趋势,年均减少面积为22.06 km^(2),年均减少0.1%。研究期间,该县各类荒漠化面积减少与扩张并存,重度、中度、轻度、微度荒漠化面积的动态度分别为-1.5%、0.2%、-0.9%、3.8%,说明荒漠化严重程度降低;研究区荒漠化总体处于稳定状态,未发生大面积并且趋势较为明显的荒漠化过程,荒漠化治理工作取得了阶段性的成果;研究区荒漠化波动下降的面积占15.2%,而波动上升的面积只占3.9%,无规律波动变化区主要分布在荒漠绿洲过渡区和绿洲边缘地区,面积达到总面积的17.7%,说明在绿洲和荒漠区交错地带,荒漠化反复变化较为活跃,是将来重点治理和修复地区之一。

We collected remote sensing images of lower reaches of the Shiyang River Basin in 1995,2000,2005,2010,2015,and 2018.We analyzed the dynamics of desertification in Minqin County by constructing desertification difference index,using RS and GIS theories and methods.We established the Albedo-NDVI feature space based on the normalized vegetation index(NDVI)and surface albedo(Albedo).The results showed that the desertification area in the lower reaches of Shi-yang River Basin accounted for more than 90%of the total area of the Minqin.Oasis scattered in large areas of desertified land.Moderate desertification accounted for more than 70%of the total area of the county.The area of desertification in Minqin showed an decreasing trend from 1995 to 2018,with an average annual reduction area of 22.06 km^(2)and an average annual reduction rate of 0.1%.During the study period,various types of desertification area contracted and expanded simultaneously,and the relative changes of severe,moderate,mild,and slight desertification areas were-1.5%,0.2%,-0.9%,and 3.8%respectively.Those results indicated that the severity of desertification was reduced.The desertification area was generally at a stable state.There was no large-scale desertification process and no obvious trends of desertification.Desertification control had achieved phased results.In the study area,the area where the desertification decreased in a fluctuation way accounted for 15.2%,while the area with increased desertification only accounted for 3.9%.The areas with irregular fluctuations of desertification were mainly distributed in the transitional area of desert oasis and the edge area of oasis,with an area of 17.7%of the total land area.The desertification change was more active in the ecotone of oasis and desert area,which was the key control and repair region in the future.