近年来的黄土高原耕地时空变化与口粮安全耕地数量分析

基于遥感调查数据集定量分析了1990—2015年中国黄土高原地区耕地的时空变化特征和口粮绝对安全最小耕地保障面积的数量变化。结果表明：黄土高原耕地面积从1990年的192 529.65 km²至2015年的182 688.50 km²，净减少了9 841.14 km²，幅度达5.11%，其中2000—2010年的减幅最大，净减少8 483.00 km²；较大的耕地动态变化图斑主要分布于中部和西部区域，细碎的变化图斑广泛分布；耕地地类转出面积（31 875.82 km²）大于转入面积（21 815.25 km²），耕地面积的增加主要由草地和林地转化而来，主要分布在灌溉农业区和东南部平原区，减少的耕地主要转化为草地和林地，主要分布在中部沟壑区的雨养农业区。此外，该时期耕地转化为建筑用地和交通用地等人工表面的面积逐渐增加，主要分布在东南部低海拔平原地区；黄土高原口粮绝对安全所需最小耕地保障面积呈明显减少特征（从1990年的70 913.37 km²下降到2015年的33 981.64 km²），占该区耕地总面积比例呈明显缩减态势（从1990年的36.83%缩减到2015年的18.60%），目前耕地总量的净减少未对口粮绝对安全的耕地保障数量造成大的影响。

Spatial and temporal changes of cultivated land and quantitative analysis of ration safe cultivated land on the Loess Plateau in recent years

Based on land cover maps and the survey data, this paper quantitatively analyzed the spatial and temporal characteristics of cultivated land on the Loess Plateau, northwest China from 1990 to 2015,and evaluated the changes in the minimum cultivated land area for grain safety. The results showed that the area of cultivated land decreased from 192 529.65 km² in 1990 to 182 688.50 km² in 2015 (decreased by 5.11%),of which the period 2000—2010 witnessed the largest change rate, with a net decrease of 8 483.00 km².The largest decrease in cultivated land was mainly distributed in central and western area of the Loess Plateau, and the finely-changed pixels were widely scattered. The areas converted from croplands (31 875.82 km²) was larger than that converted to cultivated lands (21 815.25 km²) in the period 1990—2015.The increased cultivated lands were mainly converted from grasslands and woodlands, which primarily occurred in the irrigated agricultural areas and southeastern plains of the Loess Plateau; while the decreased cultivated lands were mostly converted to grasslands and woodlands, and it was concentrated on the middle rain-fed farm areas of the Loess Plateau. In addition, the area of cultivated land converted to build land gradually increased during this period, and mainly distributed in the low-altitude plains in the southeast of the Loess Plateau. The minimum cultivated land area for grain safety decreased from 70 913.37 km² in 1990 to 33 981.64 km² in 2015, and the corresponding percentage (accounted for total cultivated land) decreased from 36.83% to 18.60%.However, the decrease of cultivated land has negligible impact on grain safety on the Loess Plateau.