过去百年青海和西藏耕地空间格局重建及其时空变化

Reconstruction of cropland distribution in Qinghai and Tibet for the past one hundred years and its spatiotemporal changes

网格化的历史土地利用/覆被数据集,可为历史气候变化和碳循环研究提供基础数据。本文估算了1910年,并订正了1950-2000年青海和西藏的省域耕地面积数据;基于现代耕地空间格局,量化了海拔高程和地面坡度与耕地空间分布之间的关系,构建了历史耕地网格化重建模型。将1910、1960、1980和2000年的省域耕地面积数据带入网格化重建模型,得到了4个时间断面的耕地空间格局。结果表明:青藏两省耕地面积1910-1950年稳定,1950-1980年快速增加,1980-2000年基本稳定,略有降低。就空间格局而言,1960-1980年,河湟谷地和"一江两河"地区土地开垦范围的扩张和垦殖强度的增长在过去百年最为明显。模型检验表明,模型重建的2000年耕地空间格局与2000年遥感数据相关系数达0.92。

Since numerical simulation has become a popular method for studying the effects of land use and land cover change on climate and environment, spatially explicit historical cropland datasets are increasingly required in regional and global climate change and carbon cycle research. In this study, using historical population data as a proxy, we estimated the provincial cropland area of Qinghai and Tibet in 1910. Based on the statistical data of the National Bureau of Statistics of China, the survey data of the Ministry of Land and Resources, and the results of some previous studies, we revised the cropland area of Qinghai and Tibet in 1950-2000. The relationship between altitude and surface slope and cropland distribution were quantified to develop the spatially explicit reconstruction model of historical cropland at a resolution of 1 km×1 km. Since the cropland area reached the maximum in the 1980 s, the satellite-observed cropland distribution extent of this time period was taken as the maximum distribution extent of historical cropland. The model developed in this research was used to reconstruct the spatial patterns of cropland in Qinghai and Tibet in 1910, 1960, 1980, and 2000. The reconstruction results show that:(1) in 1910-1950, cropland area of Qinghai-Tibet was stable, while in 1950-1980 cropland area increased rapidly, reaching 10583 km2, which is the maximum of the entire study period; in 1980-1990, cropland area decreased slightly; and in 1990-2000, cropland area increased slightly;(2) with regard to its spatial distribution, in1910- 1960, cropland expanded and land use activities intensified greatly in the Yellow River- Huangshui River Valley(YHV); in 1960-1980, cropland expansion and land use intensification occurred in the YHV, the Yarlung Zangbo River, the Nianchu River, and the Lhasa River valleys; in 1980-2000, the spatial pattern of cropland in Qinghai and Tibet remained unchanged. By comparing the reconstruction results of this study for 2000 with satellite- observed cropland distribution of the same year, we found that the correlation coefficient was 0.92 and the absolute difference followed normal distribution. The percentage of grid cells where the absolute difference is low(-10% to 10%) reached 73.29%, while the percentage of grid cells where the absolute difference is high(>40% or <-40%) was 1.94%. Incorporating more information on historical population and cropland of Qinghai and Tibet will help improve the accuracy of our reconstruction modeling. The reconstruction results of this research can be used in regional climate models to study the impact of cropland cover change on the climate and carbon cycle.