The Spatio-Temporal Variations of Land Use and Their Driving Mechanisms in Ningxia,China
QI Yuan, WANG Yi-mou, WANG Jian-hua, YAN Chang-zhen(Cold and Arid Regions Environment and Engineering Research Institute,Chinese Academy of Sciences,Lanzhou Gansu 730000,China)
Study on regional land use/land cover change with the remote sensing and GIS method is one of the important parts of the researches of global change.Ningxia Hui Autonomous Region has a special geography location,where the physical conditions characterized by much more variety,complexity and transition.The object of this paper is to analyze the spatio-temporal change of land use in Ningxia and the driving mechanisms of the change. Using remote sensing the accurate land use data is obtained.With TM image in 1990 and 2000 in Ningxia,the actuality maps of the 1990s and the 2000s are drawn by using GIS.According to the data of the 2000s,the area percentages were 46% for grassland,35.8% for farmland,10.8% for unused land,4.7% for forest,2.0% for residential area and 0.9% for water area,respectively.The land use has changed by nearly 7.8% in Ningxia from 1990 to 2000.The primary change was grassland and other land converting into farmland.Farmland area increased about 2 247 km~2 and grassland decreased about 2 375.1 km~2.Farmland had the rapidest land-use change with an annual variation rate of 0.99%;the following was residential area(0.94 %).During the fourteen years,agriculture,especially farmland,and city had developed greatly;much more grassland had been dug up as farmland. Special research of land-use change was done on several regions with similar physical and social-economic condition.The change in Ningxia has a remarkable regional difference.Different land types in different regions had different transformation.In Region Ⅰ_3,farmland had the largest change,1 160 km~2;Grassland in Region Ⅰ_3 changed 1 257.8 km~2;forest in Region Ⅱ_1 changed 85.15 km~2;residential area in Region Ⅰ_1 changed 85.09 km~2;water area in Region Ⅰ_1 changed 47.01 km~2;unused land in Region Ⅰ_1 changed 221.27 km~2.Different land uses in different regions would bring about different physical,social and economical results.The reason causing the difference is the special physical environment and social basic. The driving Mechanisms of land-use change were analyzed by using Logistic regression.Human activity is the most important driving force.The increasing farmland is dependent on the distribution of population and the social-economic base.Altitude and slope are the second important factors rather than precipitation and temperature.The people,who live in the bad physical environment,where the irrigation and topographical conditions have not advantage to the planting,develop most new farmland. Land-use change in Ningxia causes resource and environmental problems.The first is unreasonable farmland structure.The largest farmland increase takes place in Region Ⅰ_3,where precipitation is poor and terrain is cracked,but the grain yield of 80% of the total in Ningxia is in Region Ⅰ_1.The second is degradation of grassland owing to estrepement,heavy feeding and denudation,and much grassland converts to low-level farmland,sand land and unused land.The last one is desertification when plant has been damaged,because of the arid physical condition,heavy evaporation and strong wind.