A Synthetical Study On Land Use/Cover Change And Desertification In Arid And Semiarid Region

It is characterized by exiguous vegetation, weak resistance and fragility ecosystem in arid and semiarid region, minor environmental change will induce great change of ecosystem and land-cover of the earth's surface, so the forming and developing of land-cover in arid and semiarid region is greatly influenced by global change and it become a key site of global change and LUCC study. Characterized by synchronous broadly observation, speedy and economical, Remote sensing is widely used in the study of LUCC and desertification. In a word, the study of land-use/cover change and desertification by remote sensing has a great significance in arid and semiarid area.In this paper, based on 1:50,000 topographic map, field investigation data, Landsat TM image in 1987 and Landsat ETM+ image in 2002, meteorological data (from 1987 to 2002) of Zhongning county and Jingtai county, NOAA/AVHRR 8km×8km NDVI vegetation index, we processed and analyzed the data:First, we performed geometric correction, radiometric correction and atmospheric correction to the images, then validated the result of correction. To resolve the common phenomenon of same object having different spectral character and different object having same spectral character in study area, we extracted residential area and the grass in shelter belt based on knowledge discovery after supervised classification, distinguished salinized land, sandy desertification land and other harsh desert based on spectrum threshold, finally we got the accuracy assessment reports. We count the area change information of all land-cover type by transfer matrix and analyzed the spatial change of typical land-cover type. After the analysis of fractional vegetation cover, we integrated meteorological data (from 1987 to 2002) of Zhongning county and Jingtai county, NOAA/AVHRR 8kmx8km NDVI vegetation index (from 1987 to 2001) for the primary analysis of precipitation, natural vegetation and ecological environment change at the Southeastern Marginal Area of the Tengle Desert.The conclusion of this paper is as folio wings:?Based on the contrast analysis of multi-temporal remotely sensed images or quantitative study of remotely sensed images, radiometric and atmospheric correction of the images are very important. In this paper, we contrast the remote sensing images before correction with that after radiometric atmospheric correction, the result show that radiometric correction can greatly reduce the difference of different data.?The traditional auto-classification based on the spectral character always has poor accuracy because of the common phenomenon of same object having different spectral character and different object having same spectral character especially in arid and semiarid regions. Experiment results show that the classification based on multi-features has great accuracy compared with traditional auto-classification based on the spectral character.?The land-use/cover at the Southeastern Marginal Area of the Tengle Desert has taken place great change in the 15 years. The area of farmland increased 67 percent;residential area increased 149.5 percent;a great deal of cultivated land and woodland has been destroyed with the rapid development of industrialization and urbanization. There was much precipitation in 2002 compared with the precipitation in 1987, it made desert shrub got much better, much of salinized land and sandy desertification land turn into other harsh desert which has a better fractional vegetation cover. The grass and shrub in shelter belt along Baotou-Lanzhou desert-railway got little better at different extent, the protection work was efficient.? Through the analysis of NOAA/AVHRR NDVI data (from 1987 to 2001) and the precipitation data in the same period we found that grass and desert shrub was obviously restricted by precipitation. There is a lag between the growth of desert vegetation and the precipitation, furthermore, the correlation between NDVI vegetation index and precipitation two months before is much better than that between NDVI vegetation index and annual precipitation.?In the fifteen years focused on, the desert vegetation and precipitation in Jun and July had a little fluctuation increase from 1987 to middle of 1990s, but desert vegetation degenerated acutely in droughty 1991. From middle of 1990s, desertvegetation started to degenerate because of precipitation reducing, after then the ecological environment started to deteriorate, NDVI vegetation index and precipitation got the minimum in 2001. In 2002 the desert vegetation had an obvious recovery resulted from the precipitation increasing and grazing forbidden policy.?Result from much precipitation in 2002 compared with that in 1987 and grazing forbidden policy, the desert shrub got much better, much of salinized land and sandy desertification land converted into other harsh desert which has a better fractional vegetation cover, the ecological environment ameliorates. However, the grass and shrub in shelter belt in northwest margin of the oasis, both sides along the Yingshuiqiao-Yangulatu desert road, the farmland margin in the Nanshantaizi, sand desertification is still smart.