Dynamic Characteristics of the Impervious Surface Changing in Different Districts in Beijing

By using different periods of Landsat MSS/TM imagery,an analysis has been done,which is about three times of impervious surface's dynamic character in nine representative counties in Beijing. The result suggested that after the nearly 20 years of development,the classification transformed into the impervious surface has regional difference and dynamic characteristics because of various historical reasons and position.In terms of area,the newly increased impervious surface mainly concentrated in the developing new counties,including Changping,Tongzhou and Shunyi,their growth rate and the sum of the impervious surface was far beyond the expanding area like Haidian,Chaoyang,Fengtai and Shijingshan. Early in each district,the increasing area and the speed of impervious surface was relatively quite small,all of them became greatly accelerating In the middle and finally slowed down in the late. The impervious surface percentage in the classification showed that the proportion in the expanding area was roughly the same with the cultivated land and green space at the beginning(1992) and became dominant(2007). Then it became overwhelming and exceed 50% in the whole area(2011). This situation indicated that the land-use structure had changed in quality and the function of agriculture has shrunk a lot. Although the proportion of impervious surface in the new district were on the rise in each period,the farmland and green space were the majority in the land-use types. As to the source of the impervious surface,the new district depended on the cultivated land and the expanding area derived from the green space and the farmland from 1992 to 1999. In the stage from 1999 to 2007,the cultivated land conversion percentage has all risen in each county. When it comes to the last period,only the new district depended on the cultivated land as the source of the impervious surface. The trend that farmland and green area were transformed into the impervious surface has been controlled and the policy of ecological environment protection in city initially appeared.