近20a雅鲁藏布江流域冻融侵蚀演变趋势

The Trend of Freeze-thaw Erosion in Yarlung Zangbo River Basin in Nearly Twenty Years

西藏冻融侵蚀面积约占中国的冻融侵蚀面积的73％.采用1990年、2000年和2010年3期TM影像、土地利用图和植被类型图相叠加,对雅鲁藏布江（简称雅江）流域近20 a的冻融侵蚀进行目视解译,并且统计冻融侵蚀强度和侵蚀面积.结合气温、降水和植被覆盖度的变化,探讨引起冻融侵蚀面积和强度变化的原因.研究结果表明：1.近20 a雅江流域冻融侵蚀总面积略有下降,下降比例约为3.5％;轻度侵蚀区持续增加,面积由1990年的21213.6 km2增加到2010年的31 526.2 km2,增加幅度为56％;中度侵蚀区持续减少,面积由1990年的55 964.26km2减少到2010年的42 718.12 km2,减少幅度为23.6％;重度侵蚀区面积变化不显著.至2010年雅江流域的侵蚀格局发生改变,由原先的中度侵蚀主体型逐步向轻度侵蚀、中度侵蚀混合型过渡.2.雅江流域冻融侵蚀主要分布在北部高海拔地区,南部湖盆谷地分布较少,流域内冻融侵蚀主要集中在海拔4500～6000 m范围内.近20 a间流域内重度侵蚀区逐渐向东移动,由日喀则北部地区渐移至拉萨、那曲、昌都一线.侵蚀强度整体呈现减弱趋势,在日喀则地区,林芝地区和山南地区均出现轻度侵蚀逐渐替代中度侵蚀的现象.

Freeze-thaw erosion area in Tibet accounted for about 73% of the area in China, and it has become one of the three types of soil erosion, we get the freeze-thaw erosion area by visual interpretation,cover three stage TM image, land use map and vegetation type map for interpretation, we Statistics the area and the intensity of erosion. Results show that ： （ 1 ） The freeze-thaw erosion area slightly in Yajiang River Basin in recent twenty years, and the decline in the ratio about 3.5%. Mild erosion area increase continuously, from 21 213.6 km2 in 1990 to 31 526.2 km2, increased by 56%. Moderate erosion area continued to decline, area reduced to 42 718.12 km2 from 55 964.26 km= in 1990, decreased by 23.6%. Severe erosion area did not change significantly. In 2010 Yajiang watershed erosion pattern happening change, already from the original moderate erosion main body into mild, mod- erate erosion erosion of mixed type. （2）The freeze-thaw erosion areas of Yarlung Zangbo River Basin mainly dis- tribute on the Northern region with a elevation range between 4 500 to 6 000 kilometers, comparatively speaking, freeze-thaw erosion in Southern lake basins and valleys is not that serious. For nearly two decades, Severe erosion areas of Yarlung Zangbo River Basin have been moving eastward from the north Xigaze to areas along Lhasa, Nagqu and Chamdo. In a whole, soil erosion in this area is decreasing, it is slight erosion displace moderate erosion gradu- ally in areas such as Xigaze, Nyingtri and Shannan.