1990-2010年中国土地覆盖时空变化特征

Spatio-Temporal Characteristics of Land Cover Changes in China During 1990-2010

本文基于CG-LTDR土地覆盖数据产品,利用GIS空间统计等方法分析了中国1990-2010年土地覆盖的变化特点。与参考数据的比较检验表明,CG-LTDR土地覆盖数据在中国具有与其他同类数据相当甚至更高的分类精度。经逐年的长时间地表覆盖数据分析发现,由于受气候与人为因素影响,土地覆盖类型有明显的年际变化波动,尤其是云南-内蒙一线的干旱区与湿润区的过渡带。1990-2010年中国的林地和荒漠呈增加趋势,而草地和耕地呈减少趋势。利用5年的合成数据分析其年际变化,结果显示1990-2000年土地覆盖类型变化大,2000-2010年的变化较为平缓。在几种主要覆盖类型中,林地增加最明显,这主要与东南地区大部分耕地、西南和东北地区大面积草地转变为林地有关,但也有部分省份由于树木砍伐和农耕区扩张导致林地面积减小。耕地面积占比最高,其减少趋势主要与耕地变为林地和草地有关。南部的耕地减少最明显,北部略有增加,新增耕地的重心从东南向北转移。林地的增加趋势与耕地的减少趋势主要与全国大范围的退耕还林工程和生态保护政策有关。草地主要分布在生态脆弱区,其面积减少最显著,在西南及东北部分地区主要是草地变为林地,在内蒙中东部-陕西北部一线发生草地与耕地相互转换,而在内蒙北部-青藏高原一线有草地与荒漠的互相转换,在土地覆盖类型交错区,其利用类型容易发生改变。荒漠主要分布于西北地区,由于受到草地退化等因素影响,荒漠化趋势在进一步加剧。

Based on CG-LTDR datasets, the land cover change and distribution characteristics during 1990-2010 were analyzed in China using the GIS spatial statistical analysis and other mathematical statistics methods.Compared with the reference data of CLUD, CG-LTDR land cover data has a higher classification precision. The new datasets show that the land cover indicates obvious interannual evolutions due to the climate and human activities, especially in the semi-arid and semi-humid areas distributed along Inner Mongolia to Yunnan Province.The synthetic land cover data for 5 years were used to eliminate the interannual fluctuations and to increase accuracy. The results show that the land cover types in China had changed dramatically during 1990-2000 and indicated a relatively smooth pattern during 2000-2010, which is related to the application of national policy and economic development. Among the four major land cover types, the increase of woodland area was the most significant, which is mainly due to the land use transformation from farmland to woodland in the Southeast China, and grassland into woodland in the southwest and northeast part of China. But due to the deforestation and cropland expansion, the coverage of woodland was decreased in some of the Northeast and Northwest China regions. Farmland has the largest coverage in China, while its decreasing trend is mainly caused by its transformation toward woodland and grassland. The most significant decrease of farmland appeared in the south part of China, while a slight increase was revealed in some of the Northern China. The increase of woodland and decrease of farmland were related to the national policy of ＂returning farmland to forest＂ and relevant ecological environment constructions. Grassland was mainly distributed in the ecological fragile region, and was prone to convert into other land cover types. Moreover, grassland decreased most evidently around China, because of the changes among different land cover types. To be specific, grassland was turned into woodland in Southwest China. And, grassland and farmland was interactively converted into each other along the conjunction areas from the middle east of Inner Mongolia to the north of Shaanxi Province. Additionally, grassland and bareland was converted interactively along the regions from the northern of Inner Mongolia to Tibetan Plateau. The bareland was mainly located in the Northwest China, while showing an increasing trend due to the degradation of grassland.