作 者 ：李海东*,沈渭寿,邹长新,孙明,佘光辉
期 刊 ：生态学报 2010年 30卷 21期 页码：5716~5727
关键词：拉萨机场；风沙化土地；空间分布；演变趋势；气候变化；
Keywords:Lhasa Airport, aeolian sandy land, spatial distribution, evolution of desertification, climate change, Tibet,
摘 要 ：运用3S技术，通过大量野外调查与遥感数据人机目视解译方法，解译了拉萨机场周边5县1990年、2000年和2008年3期近20a遥感数据，并结合1∶250000 DEM数据和气象资料，分析了风沙化土地的空间分布及其随高程、坡向的变化特征，以及近20a来风沙化土地的演变趋势和驱动因素。结果表明：(1) 2008年拉萨机场周边各类型风沙化土地共有42462.38hm2，其中，由风积和风蚀活动引起的风沙化土地面积分别为33088.87hm2和9373.51hm2，风积沙地比例为77.93%。(2) 拉萨机场周边0—20km风沙化土地面积为14200.54hm2，20—40km面积为10351.03hm2，在40km内风沙化土地占总面积的57.82%。(3) 拉萨机场周边风沙化土地增长趋势开始放缓，近20年增长率为53.78hm2/a，其中，20世纪90年代增长率为62.83hm2/a；2000年后增长率为43.72hm2/a。(4)近20a间，气温平均增长率1990—1999年和2000—2008年分别为1.29℃/10a和1.96℃/10a。气温升高是造成风沙化土地进一步发生发展的主要动力。平均风速下降和降水量增长是抑制其发生发展的原因之一。(5) 2000年后拉萨机场周边河谷地段人工林面积大幅度增加，裸露河床面积显著减少，在一定程度上减缓了河床沙源向河岸及山坡的搬运，这是近10a风沙化土地增长速度有所放缓的原因之一。
Abstract:We studied sandy desertification in five counties near Tibet′s Lhasa Airport, in the middle reaches of the Yarlung Zangbo River valley. We analyzed the spatial distribution of aeolian sandy land and its evolution since 1990 by interpreting Landsat data from 1990, 2000, and 2008 using geographic information system (GIS) technology. The results were then matched to a regional 1∶250 000 digital elevation model using the GIS software. The driving causes of aeolian sandy desertification were analyzed from the perspectives of climate change and human vegetation restoration activities to clearly define the current situation and to provide guidance for future vegetation restoration. The total area of aeolian sandy land in 2008 was 42 462.38 hm2, versus 41 440.61 hm2 in 1990 and 42 068.89 hm2 in 2000, representing a 2.5% increase from 1990 to 2008. The areas of aeolian sandy land caused by windblown sediments and wind erosion in 2008 totaled 33 088.87 hm2 and 9373.51 hm2, respectively, representing 77.9% and 22.1%. The area of aeolian sandy land totaled 14 200.54 hm2 within 20 km from Lhasa Airport and 10 351.03hm2 between 20 and 40 km from the airport. The aeolian sandy land mainly occurred at elevations from 3600 to 3800 m; sandy land at these elevations accounted for 77.9% of the total. The aeolian sandy land was mainly found in flat areas, which accounted for 45.4% of the total, versus 13.8% and 13.4% for southeast- and south-facing slopes, respectively. The area of aeolian sandy land has increased slowly throughout the study period, at a rate of 62.83 hm2/a in the first 10 years and 43.72 hm2/a in the last 9 years, representing a gradual slowing. However, the overall rate of expansion since 1990 averaged 53.78 hm2/a. The increased area of sandy land mainly resulted from the region′s harsh climate and fragile environment, combined with a warmer and drier climate that accelerated the desertification process. We obtained meteorological data from 1957 to 2007 from two monitoring stations in the study area (Lhasa and Zedang), and wind speed and direction data from 1980 to 2006 from the Lhasa Airport meteorological station. During this period, the study area has grown increasingly warm. The average rates of temperature increase from 1990 to 1999 and from 2000 to 2007 were 1.29 and 1.96℃ per decade, respectively. Both are much higher than the overall average of 0.34℃ per decade since 1957. The rainfall varied widely during the study period. The average rate of precipitation increase has been 5.56 mm per decade since 1957. The annual rainfall from 1957 to 2007 averaged 419.90 mm, versus averages of 437.20 mm from 1990 to 1999 and 474.06 mm from 2000 to 2007 (both above the long-term average). The annual mean wind speed from 1980 to 2006 averaged 2.08 m/s, versus averages of 1.90 m/s from 1990 to 1999 and 1.88 m/s from 2000 to 2007 (both below the long-term average). The air temperature increase therefore appears to be the main driving factor for the development and spread of aeolian sandy land. The slightly higher precipitation and lower wind speed in this region since 2000 were natural factors that slowed the expansion of aeolian sandy land during this period, and an increased area of forest plantations, combined with a declining area of bare riverbeds, also slowed this expansion, possibly by preventing or reducing sand transport from riverbeds and dunes to river banks and hillsides in the valley.
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