A Spatiotempral Analysis of Land Use Change and its Driving Forces in the Upper Reaches of the Chaobai River, North China
潮白河上游土地利用的时空变化特征与驱动力分析

The upper reaches of the Chaobai River are the water supplying source of the Miyun Reservoir that supplies a major part of water consumption of Beijing. In the past decades, the runoff in the Chaobai River showed a decreasing trend. In addition to the increased water use in the reaches, land cover change is also acknowledged as an important one of the factors affecting the runoff. To contribute to the understanding of hydrological variation in the river, this paper conducts a spatial and temporal analysis of land cover changes in the 1990s, taking small watersheds as the study unit using digital land use maps in 1990 and 2000, with the help of ARCVIEW and EXCEL software. Further, it identifies major factors affecting the land cover change. In this region, a large amount of grassland and cultivated land was transferred to forestland in 1990~2000, and thus resulted in a substantial increase of forest coverage but a great shrinkage of farmland and grassland. In the 10 years, forestland increased 24.02×104 ha, while farmland and grassland reduced 6.28×104 ha and 17.19×104 ha, respectively. Water area shows a great shrinking, with the area decreased by 60%, reflecting the decreased availability of water resource. Built-up area had a marketable expansion, increased by 36.5%. Spatial analyses indicate that land use changes are greater in Chicheng County and in the bordering areas of several counties than in other areas. Three major factors contributed to the land use changes in this region, i.e., ecological rehabilitation, afforestation, and agricultural restructuring. Population growth and urbanization rate were low in the period of 1990~2000, and have a limited effect on the land use change.