Analysis On Land Use Change During The Last 15 Years And Its Trend In Xiji County

In order to studying the influence of the policy of converting farmland into forests to the land use change, the Xiji County is taken as a case, where the policy is carried on earlier than most of other areas in Loess Plateau, and TM images of 1990 and 2005 are chosen to analyze the rule of land use change of Xiji County by establishing the land resources information system. In the process of analyzing, the characteristic of topographic/geomorphologic types and land resources can be found that there has an obvious difference between in the south and north part of Xiji County. Because of this, we must study the land use change associated with geomorphologic factors but not only from the perspective of land use structure and its inner conversion process. In respect of the method of ectracting the geomorphologic types is that: Firstly, the digital elevation model (DEM) is used to divide the boundary of hill/ridge, gully and valley/cleuch in hilly and gully loess regions or mountain and valley/cleuch in rocky mountain area. Secondly, by means of hypothesis testing, the turing degrees in stead of the boundary will be sample verificated. Then the geomorphologic calssification can be established by close dividing the slope of Xiji County to further analyse the land use change. Afterwards, Markov chain model is used to forecast the trend of land use change on the whole County and the change on each geomorphologic type, which can provide a scenario for policy makers to consider the future land use change in this region.The results show that:(1) From the years of 1990 to 2005, the land use types whose change obviously are cultivated land, forest land, grassland and unused land, and the proportion of cultivated land, forest land, grassland has varied from 1.88:1:1.50 in 1990 to 1.26:1:1.09 in 2005, the ratio of vegetation cover is becoming more and more high. The land of 26.81% appears conversion in total, and cultivated land and grassland in 1990 have mainly converted to other land use types, then forest land and cultivated land in 2005 have mainly been converted from others in 1990.(2) During the last 15 years, cultivated land and forest land have generated obvious change on the various geomorphologic regions, and the land use types on the geomorphologic types of 7 and 10 appears significant change. And by analyzing the land use conversion process on the different geomorphologic regions, we can find that there is a recurrent phenomenon of farmland converted into forests or grass and second ploughing of forest land and grassland. (3) On the premise that the land use policy never change following time, the trend of land use change wherever on anyone of geomorphologic regions is forest land, residential and industrial land and traffic land rising, but cultivated land, grassland, unused land and water area dropping. However, the average change ranges of them have close connection with different geomorphologic regions.