Study On The Dynamic Change Of Vegetation In Northwestern China Using RS And GIS

It's well known that earth vegetation and global climatic change have effects on each other. They affect each other in change direction. Therefore, the vegetation change has become the main and direct object of the global climatic study. Because of the special geographical position and the frail ecological environment in northwest China, the vegetation is much sensitive to the climatic change. Thus, the research on vegetation dynamic change in a long time series makes extremely great sense. With the help of remote sensing and the GIS technology, the NDVI time series data in Chinese northwest area during 1982-2003, precipitation and the temperature data during 1981-2002 and the two land use maps in 1986 and 2000 have employed to study the SINDVI change of different land use, the relationship between climatic factors and vegetation SINDVI in northwest China during this stage. Some results are as follows:(1) The two biggest landscapes in northwest China is no used land and low cover lawn, whose SINDVI is 0-1. The total area of these kinds of landscapes has reduced continuously. The two kinds of landscapes whose SINDVI value is 2-6 are the prevailing species in the vegetation landscape. These two kinds of land utilization type is mainly the dry crop lands, middle and low cover lawn and the cities land. The total area has increased. With vegetation SINDVI value increasing, the landscape areas and connects decrease gradually. These landscapes, as small patches, are set among other landscapes.(2) The vegetation landscape in northwest China has been improved as a whole, but degenerated in some areas during research period (1982-2003, 22year); the vegetation condition improves first, then degenerates again. The vegetation area has expanded from 49.78% to 52.85% of the total land area. Average SINDVI rose by 0.3. The quantity of high SINDVI vegetation has reduced. The time series SINDVI show that the complex degree of landscape shape in an ascending order from small to big is 1988-1993, 1994-1998, 1999-2003, and 1982-1987. The shape of northwest local landscape experienced a process from complex to simple, then again to complex. Northwest local SINDVI value increase universally during 1982-1993, SINDVI of landscape type during 1993-1998 not only increases, but also reduces. In 1998 later, vegetation SINDVI presents the tendency which reduced.(3) Three types with SINDVI value between 0.01-4 are most active. The landscape conversion rate is about 20%. Basically, the conversion would cover four SINDVI types. But the annual change rates of other landscape types are smaller; correspondingly, the landscape survival rate is higher. The SINDVI value shows a general increase during 1982-1993. The conversion rate of identical landscape type to the higher SINDVI type is higher than that to the lower SINDVI type. The SINDVI during 1994-2003 is just the opposite, which has reduced generally. The change situations of various landscapes type are not same. The vegetation in Chinese northwest area has improved at first, and then degenerated again during the 22 years. As time goes by, the improving speed of same vegetation SINDVI type has slow down gradually, but the degeneration speed has speeded up.(4) The SINDVI of no used land distributes mainly in 0-0.01. SINDVI of 74.77% sands distributes in 0-0.01. SINDVI of Paddy field is higher than 8. The SINDVI of 73.75% mountainous region paddy field is about 10-12. The SINDVI of Knoll paddy field distributes completely in 8-12. The SINDVI of dry land and forest land is higher but more scattered, which mainly distributes in 10-16. The SINDVI of lawn and water body is also more scattered relatively. But the SINDVI of cities construction land is mainly distributes in 2-6, which is more concentrative comparing to the countryside residential area. Because of the continuous degeneration in prairie and the unceasing enhancement of city afforestation level, the SINDVI of prairie has increased but the value of cities land has reduced. The SINDVI of no used land is decreasing gradually.(5) The SINDVI of each land use type show a basic order: The mountainous paddy field > the knoll paddy field > the mountainous arid cropland > the forest land > the slope arid land > the bush forest > the stocked land >the plain paddy field > the countryside residential area > other forest lands > the high cover lawn > the plain arid land > the knoll arid land > the rivers and creeks > the middle cover lawn > the reservoir and pond > the cities lands > the bog > the beach > the lowly cover lawn > other lands> the lake > the bare land > the permanent glacier snowy area > salt alkaloid > the bare rock gravel > Gobi > the sand.(6) The relativity of SINDVI and the precipitation is greater than that of the SINDVI and the temperature in northwest China. But the influences of precipitation and temperature on the SINDVI of different climatic vegetations are quite different. The temperature of dry area was rising, the precipitation was decreasing and SINDVI in the area was variety in the past 22 years. The inconformity change of SINDVI, precipitation and temprture is resulted by irrigation; The climate was became from wame and dry to wame and wet.SINDVI have bigger increase than other areas in the past 22 years in SINDVI is 2.0 to 4.5 regions, it is about 0.5; The changes of precipitation and temperature hanve little influence to SINDVI in the areas of agriculture and forestry. It is said that the SINDVI influenced by many factors in the area.It is difficult to discriminate and divide landscape type because low spatial resolution NOAA/AVHRR data will affect the accuracy of the results. In order to enhance the accuracy, we will choose remote sensing data with a suitable resolution and make a corresponding processing according to our study in the future.