黄河十大孔兑流域林草植被覆盖度的遥感估算及其动态研究

Study on shrubs-herbs-arbor vegetation coverage and dynamic changes in the ten tributaries of Yellow River in Inner Mongolia by remote sensing method

利用多源遥感数据,采用基于归一化植被指数的像元二分模型反演出1980、1998、2010、2014年4个时期的植被盖度,在此基础上分析并揭示黄河十大孔兑流域林草植被覆盖度的时空变化规律.结果表明:1)1980—2014年间,十大孔兑流域林草植被覆盖度呈现持续增加趋势,由1980年的9.29%提高至2014年的37.80%.1998年后,全流域林草植被盖度增加速率显著加快,林草植被盖度恢复主要表现为中等覆盖度的面积比例增加.2)近35年来,十大孔兑流域植被变化以稳定和完全恢复类型为主.研究区内完全恢复、恢复和轻微恢复3种植被变化类型占总面积的73.09%,严重退化、退化和轻微退化3种类型占总面积的2.72%.3)1980—2014年间,十大孔兑各个典型地理单元内林草植被盖度均呈增加趋势,除下游地区外均表现为1998年后林草植被盖度增加更为迅速.1980年,十大孔兑流域典型地理单元林草植被盖度由大到小排序为:上游西部、上游东部、下游、中游东部、中游西部.1998—2014年间典型地理单元林草植被盖度由大到小排序变化为:中游东部、上游东部、上游西部、中游西部、下游.1998年后实施的退耕还林(草)等工程是该地区植被覆盖度增加的主要原因.

A series of water and soil conservation measures and river regulation projects were vigorously promoted and implemented in the ten tributaries of Yellow River in Inner Mongolia in recent decades. These include returning farmland to forest and grass, planting trees and grass, which led to significant changes in vegetation cover of underlying surface. Dimidiate pixel model based on NDVI was adopted to calculate vegetation coverage in 1980, 1998, 2010 and 2014 using multi-source remote sensing data, spatial and temporal variations of shrubs-herbs-arbor vegetation coverage were analyzed. It has been found that from 1980 - 2014, the shrubs-herbs-arbor vegetation coverage in the ten tributaries showed a consistent growth trend from 9.29 in 1980 to 37.80% in 2014. The increase rate of shrubs-herbs-arbor vegetation coverage was significantly faster in the whole basin after 1998. The main feature of coverage restoration was that the area ratio of medium vegetation coverage increased. In the past 35 years, complete recovery type and stable type were the main vegetation change types. The three vegetation changing types that contain complete recovery, recovery and slight recovery types have accounted for 73.09o/60 in the whole basin. Total areas of serious degradation, degradation and slight degradation types accounted for 2. 72%. From 1980 - 2014, the shrubs-herbs-arbor vegetation coverage in all typical geographical units in the ten tributaries showed an increasing trend. The increasing rate of shrubs-herbs-arbor vegetation coverage was significantly faster, with exception of coverage downstream after 1998. In 1980, order of shrubs-herbs-arbor vegetation coverage in different typical geographical units of the ten tributaries was： western upstream〉 eastern upstream〉 downstream〉 eastern midstream〉western midstream. From 1998- 2014, the order changed to： eastern midstream〉 eastern upstream〉 western upstream〉 western midstream〉 downstream. Returning farmland to forest and grass was the main reason to increase vegetation coverage of the ten tributaries after 1998.