黄河源区沙漠化及其景观格局的变化

本研究以1975年的MSS数据、1990年和2005年的TM数据、以及2000年的ETM数据为数据源,通过遥感（RS）与地理信息系统（GIS）技术,获得了黄河源区在1975－2005年间沙漠化的发展特征,并采用景观指数运算软件（FRAGSTATS3.3）对黄河源区沙漠化土地的景观格局变化进行了分析。研究发现：在1975－1990年间,黄河源区的沙漠化土地面积大幅增加;在1990－2000年间,沙漠化土地面积保持稳定;在2000－2005年间,沙漠化土地面积出现了小幅度的减小趋势。黄河源区沙漠化土地的景观格局变化显著,在1975－1990年间,沙漠化土地发生了严重的破碎化;在1990－2000年间,沙漠化土地出现了连片的现象,从而使得沙漠化土地的破碎度有所下降,景观多样性降低;在2000－2005年间,沙漠化土地破碎度的增加,斑块形状趋于复杂。

Desertification and change of landscape pattern in the Source Region of Yellow River

The Source Region of Yellow River is located in the northeast of Qinghai-Tibet Plateau, with an area of 13.14104 km2. The Source Region of Yellow River plays important roles in water conservation, bio-diversity protection and wetland conservation. Nevertheless, the rapid climate change in the Qinghai-Tibetan Plateau has induced lots of environmental problems such as glacier retreat, permafrost degradation, aeolian desertification, and grassland degradation. For the last decade, the eco-environmental problems in the Qinghai-Tibetan Plateau have been receiving increasing attention due to global warming and intensifying regional development. Our recent investigations revealed that aeolian desertification became a severe environmental problem in the Source Region of Yellow River. We therefore conducted this study to fully understand the development processes and the changes of landscape pattern of aeolian desertification in these regions. The development of aeolian desertification between 1975 and 2005 is identified by using remote (RS) sensing and geographic information system (GIS) methods. Remote-sensing data used in this study includes: Landsat multi-spectral scanner (MSS) images of 1975 with spatial resolution of 80-m, Enhanced Thematic Mapper (ETM ) images of 2000 with resolution of 30-m, and Thematic Mapper (TM) images of 1990 and 2005 with resolution of 30-m. We selected images recorded between June and October, when vegetation grew well, because aeolian desertified lands are more easily recognized during this period. Thematic maps, including land maps and geomorphologic maps, were used as supplementary data sources. The result shows that the area of aeolian desertified land increased at a rate of 151.74 km2 a-1 between 1975 and 1990 (slightly, moderately and severely desertified lands increased at a rate of 40.49, 70.96 and 40.25 km2 a-1, respectively.), increased at a rate of 1.57 km2 a-1 between 1990 and 2000 (moderately and severely desertified lands increased at a rate of 9.48 and 6.29 km2 a-1, respectively, and slight ly desertified land decreased at a rate of 14.20 km2 a-1. ), and decreased at a rate of 54.66 km2 a-1 between 2000 and 2005 (slightly and moderately desertified lands increased at a rate of 15.51 and 17.34 km2 a-1, respectively, and severely desertified land decreased at a rate of 87.51 km2 a-1.). Furthermore, landscape software Fragstats 3.3 was used to analyze the landscape pattern of aeolian desertified land in the Source Regions of Yellow River. It was found that the landscape pattern changed significantly, the fragmentation degree of aeolian desertified land increased rapidly between 1975 and 1990, decreased slightly between 1990 and 2000, and increased again between 2000 and 2005.The patch shape of aeolian desertified land became more irregular. Factors responsible for the land desertification include increasing temperature, decreasing precipitation, over-grazing, drainage of water systems, land reclamation for agriculture and rodent damage. Of these factors, increasing temperature, over-grazing, and drainage of water systems appear to have been the key factors. So we suggest that human behavior must be adjusted to control the expansion of aeolian desertified lands and to rehabilitate the aeolian desertified lands. The "tragedy of the commons" has led to problems such as over-grazing in common pasture areas throughout the study area, so it will be necessary to adjust the grazing rights of local people to prevent further over-grazing. It will be very important to strengthen the knowledge of environmental protection by local people so they will understand the need for such changes. In addition, the government must find alternative forms of employment that will be attractive to these people and that will sustain them in the long term so that they are not forced to return to their old, unsustainable practices.