基于RS和GIS的玛曲高原土地沙漠化时空演变研究

基于RS和GIS空间分析技术,以玛曲高原多期Landsat遥感数据为主要信息源,监测分析了1977—2014年玛曲高原沙漠化土地的时空演变规律。结果表明:近40年来玛曲高原的土地沙漠化经历了迅速发展—缓慢发展—急速逆转—缓慢逆转—快速逆转的变化过程。1977—1995年玛曲高原沙漠化处于快速扩张阶段,年均扩张速率为3.01%;1995—2014年沙漠化扩张趋势出现逆转,年均逆转速率为4.14%。沙漠化土地的发展和逆转区域主要分布在东北部欧拉秀玛乡和尼玛乡黄河沿岸、东南部采日玛乡和曼日玛乡沼泽区、西南部齐哈玛乡和中部阿万仓乡黄河支流两岸。玛曲高原沙漠化土地的发展和逆转过程并非逐级递增或递减,而是在15—20年内交替出现,不同等级沙漠化土地之间的转移也存在明显的跃变。从整体来看,玛曲高原土地沙漠化呈现逆转趋势,区域生态环境得到明显改善。

Spatio-temporal change in desertification of the Maqu Plateau based on RS and GIS

The Maqu plateau, an important part of the Qinghai-Tibet plateau, is the main water conservation area in the upper reaches of the Yellow River. In recent years, under the influence of natural environmental and human activities, the ecologically sensitive Maqu plateau area has experienced environmental problems such as glacier retreat, permafrost degradation, aeolian desertification, and grassland degradation. The Maqu plateau is one of the largest pasture lands in Asia, with a rangeland area of 8.58×10⁷hm². In the past decade, the eco-environmental problems of the Qinghai-Tibetan plateau have received increasing attention owing to global warming and intensifying regional development. The aim of this study was to quantify the developmental processes in these region, as well as any changes in the spatial distribution of land desertification. We used remote sensing (RS) and geographic information system (GIS) technologies, and applied multi-temporal Landsat imagery to investigate the spatio-temporal development of land desertification in the Maqu Plateau during 1977-2014. The remote-sensing data used in this study include:Landsat multi-spectral scanner images from 1977; Thematic Mapper images from 1989, 1995, 2006, and 2014; and Enhanced Thematic Mapper images from 2001 and 2010. We mainly selected images recorded between June and October, because aeolian desertified lands are more easily recognized during this period of greater vegetation growth. Our results indicated that the area of desertified land in the Maqu plateau had experienced five main phases:rapid development, where the area of aeolian desertified land increased at a rate of 2004.6 hm²/a between 1977 and 1989; slow development, where it increased at a rate of 57 hm²/a between 1989 and 1995; rapid reverse, where it decreased at a rate of 3868 hm²/a between 1995 and 2006; slow reverse, where it decreased at a rate of 893.4 hm²/a between 2006 and 2010; and, fast reverse, where it decreased at a rate of 2129.3 hm²/a between 2010 and 2014. The area of desertified land expanded rapidly between 1977 and 1995, with an average growth rate of 3.01% per year. An obvious decrease in the area of desertified land was observed from 1995 to 2014, with an average reversal rate of 4.14% per year. The areas affected by the development and reversal of aeolian desertification were mainly distributed alongside the Yellow River, including near the Oulaxiuma and Nima villages of the northeastern region, the marshlands of the Cairuma and Manrima villages in the southeastern region, and the riversides of tributaries to the Yellow River near the Qihama and Awancang villages of the southwestern region. We found that the spatial distribution of aeolian desertification changed significantly over time, with fragmentation of the desertified land increasing rapidly between 1977 and 1995. Aeolian desertification in the Maqu Plateau has not been progressive, but instead, it has been an alternating process of development and reversal approximately every 15 to 20 years. There was an abrupt change in the desertification level of lands in different levels of the plateau. Overall, we found that the trend of aeolian desertification in the Maqu plateau had been reversed and the local environment had improved since 1995.