A major monitoring area, a part of the middle reaches of Heihe basin, was selected. The Landsat TM data in summer of 1990 and 2000 were used with interpretation on the computer screen, classification and setting up environmental investigation database (1:100000) combined with DEM, land cover/land use, land type data and etc., according to the environmental classification system. Then towards to the main problems of environment, the spatial statistical analysis and dynamic comparisons were carried out using the database. The dynamic monitoring results of 1999 and 2000 show that the changing percentage with the area of 6 ground objects are as follows: land use and agriculture land use increased by 34.17% and 19.47% respectively, wet land and water-body also increased by 6.29% and 8.03% respectively; unused land increased by 1.73% and the biggest change is natural/semi-natural vegetation area, decreased by 42.78%, the main results above meat with the requirements of precise and practical conditions by the precise exam and spot check. With the combinations of using TM remote sensing data and rich un-remote sensing data, the investigations of ecology and environment and the dynamic monitoring would be carried out efficiently in the arid area. It is a dangerous signal of large area desertification if the area of natural/semi-natural vegetation is reduced continuously and obviously.
The study area of this paper is Dingxi County, a typical loess gully-hilly region of the semi-arid regions. The land use maps in 1990 and 2000 were compiled from the Landsat TM images and other data resources. There are 9 kinds of land use types. The slope data derived of contour lines. Referring to some metrics of the landscape ecology, 10 metrics were selected or developed for quantifying the land use characteristic, monitoring the land use changes and analyzing the relationships between land use, land use changes and the topographical condition, governmental policies of the Dingxi County. Some conclusions were obtained. The selected metrics can quantify the land use and land use change in typical loess gully-hilly region, Dingxi County. The land use and land use change have good spatial distribution regularities in the slope grades. The governmental policies are the primary driving factors for the land use changes in our study area. The policies are reclaiming the slope farmlands and grassland into terraces, rainfall-collection works, and reforesting and regressing some sloping cultivated lands.
Environmental evaluation and planning is a hot point of the relative science research nowadays. So the work is carried out in the Dingxi prefecture, a typical loess gully-hilly region of the semi-arid regions. The AHP method is used to evaluate the characteristic, quality, and degree and potential in use of the regional ecological environment. Then some suggestion on the ecological renovating, restoring, and planning were presented. The factors were selected according to our data resources and the factors weight is defined. The results indicate that using AHP model, the environmental evaluation can be performed in the loess gully-hilly region in northwest of China. In the study area, the quality, and degree and potential in use is not so good in the most of the study area. On the bases of quality evaluation, the environmental planning was developed.
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