1986-2015年干旱区敦煌绿洲景观的时空演变过程

基于遥感影像的绿洲景观定义及其特征,以敦煌绿洲为例,利用TM(Thermatic Mapper)遥感数据,提取了1986-2015年7期的绿洲分布影像.利用数理统计及景观分析模型,分析敦煌绿洲景观的面积变化、扩展的方向性、时空演变及景观格局特征.结果表明:近30 a敦煌绿洲面积增加了60.68％,扩张速度最快的时段为1995-2010年,主要表现为人工绿洲的扩张.绿洲景观主要向东北、正北及东方向扩展,外缘发生在天然绿洲及绿洲-荒漠交错带,内部主要分布在古河道的荒滩或复杂绿洲斑块之间,绿洲景观边界逐渐趋于规则.研究结果表明,研究时段内绿洲扩张建立在人工绿洲增加,天然绿洲萎缩的基础上,绿洲面积增加的同时也发生着严重的环境退化问题.

Spatiotemporal Evolution of Landscapes in the Arid Dunhuang Oasis during the Period of 1986-2015

The changes of oasis are the long-standing issues of human concerns in arid regions of China.The spatiotemporal change of oasis on a large regional scale by means of remote sensing and geographic information system has become as an inevitable trend.However, the basis of quantitative research of oasis was the accurate definition and reasonable boundaries of oasis.So, in this paper, the definition of oasis was summarized, and the features of oasis based on remote sensing were analyzed according to the maps, images of Google Earth and several times of field investigation.The Dunhuang Oasis is located in the arid Hexi Corridor in northwest China, a typical Gobi oasis with fragile ecology.The ecological environment in the Dunhuang Oasis was seriously affected due to the rapid growth of population and the excessive exploitation of natural resources.Therefore, in this study the Dunhuang Oasis was taken as the research area to extract its distribution on the time interval of 5 years during the period of 1986-2015 based on the TM (thermatic mapper).The variations of oasis area, oasisization and desertification during the period of 1986-2015 were estimated with a set of mathematical statistical models.The directional change of the oasis was analyzed with the barycenter transfer model and oasis extension radar map.In order to well display the distribution of the Dunhuang Oasis in recent 30 years, seven kinds of data were used to analyze the oasisization and desertification.The change of local landscape pattern was analyzed.The results are as follows:① Area of the Dunhuang Oasis was gradually enlarged by 60.68％ in recent 30 years, which was mainly for expanding the artificial oasis.It could be found that the obvious variation occurred during the periods of 1995-2000 the area was enlarged by 17.22％),2000-2005 (by 14.55％) and 2005-2010 (and by 9.76％).While the area was lowly enlarged during the periods of 1986-1995 and 2010-2015 (the area was enlarged by 1.7％ only);② The Dunhuang Oasis was expanded northeastward, northward and eastward.Most expansion of the oasis occurred as natural oasis and oasis-desert ecotone in the peripheral regions of the oasis.The expansion of inner oasis included the desolated beaches of the ancient river and the complicated patches of oasis with the body internally filled expansion and progressively peripheral extension.Therefore, expansion of artificial oasis broken the original "natural green barrier", leading to a reduction of natural vegetation and a simple vegetation structure.With the increase of patches, the oasis landscape patches tended to be simple and uniform, which showed that human activities affected significantly the spatial distribution of oasis;③ With the rapid growth of population, the water consumption was also increased coupled with the excessive exploitation of natural resources in the upper reaches of the Dang River and Shule River,which leaded to the surface water shut-off, over pumping of groundwater and inadequate water conservation in some regions, as a result a severe shortage of water resources occurred in the Dunhuang Oasis.Especially in the northeast and north of the study area, the edge of the oasis was very unstable not only in the expanded area but also in the retreat area.The oasis became extremely fragile due to human disturbance, therefore, the residents in the study area should eliminate the extensive and predatory exploitation, and maintain a rational planning and appropriate development.These results also revealed that the expansion of artificial oasis was at the expense of shrinking the natural oasis.