长江黄河源区高寒植被变化的NDVI记录

使用8 km分辨率Pathdfinder NOAA-AVHRR/NDVI时间序列数据, 对青藏高原长江、黄河源区1982~2001年地表植被覆盖的空间分布和时间序列变化进行了分析, 并在典型区NDVI与气温、降水量和浅层地温单相关关系分析的基础上, 在不考虑地温作用和考虑地温作用两种条件下, 构建了NDVI与气温、降水量和浅层地温的统计模型。结果表明：近20年来江河源区的植被覆盖总体上保持原状,　局部继续退化。黄河源区的扎陵湖、鄂陵湖周边及其北东部地区、巴颜喀拉山北麓的多曲源头地区、长江源区的曲麻莱和治多一带、托托河沿至伍道梁之间的青藏公路两侧一定范围、格拉丹冬局部地区年NDVI减少显著,　幅度在0%~20%之间,　植被退化严重。江河源区年NDVI的变化, 即植被覆盖状况的好坏主要受温度, 尤其是40 cm附近地温的影响, NDVI对40 cm的地温变化极为敏感。在江河源多年冻土区, 冻土冻融过程不仅与地温变化息息相关, 而且影响土壤含水量的多少, 冻土的退化将会直接影响该区植被的生长。

NDVI Reflection of Alpine Vegetation Changes in the Source Regions of the Yangtze and Yellow Rivers

The spatial distribution and dynamic change of vegetation cover in the source regions of the Yangtze and Yellow rivers of the Tibetan Plateau are analyzed in recent 20 years based on 8 km resolution multi-temporal NOAA AVHRR-NDVI data from 1982 to 2001. The data are from NASA Pathfinder AVHRR Land datasets. On the basis of simple correlation analysis of air temperature, precipitation, shallow ground temperature and NDVI, which is 3×3 pixel at the center of Wudaoliang, Tuotuohe, Qumalai, Maduo, and Dari meteorological stations, the statistical models of air temperature, precipitation, shallow ground temperature and NDVI are constructed in this paper under two conditions—considering ground temperature action and not considering ground temperature effect. The results show that as a whole vegetation cover keeps original conditions basically in recent 20 years, vegetation continues to degrade in local areas of the source regions of the Yangtze and Yellow rivers. Remarkable decrease regions in NDVI are Zhaling Lake and Eling Lake edges, areas to the east and the north of the lakes, the headwater area of Duoqu river in the northern foot of Bayan Har Mountain in the source region of the Yellow River, part areas in Geladandong region, some regions along the Qinghai-Xizang Highway between Tuotuohe and Wudaoliang, Qumalai and Zhiduo belts in the source region of the Yangtze River. Decrease range of NDVI is 0% to 20%. Vegetation degraded very severely in the above-mentioned regions. In the source regions of the Yangtze and Yellow rivers annual NDVI changes, namely good or bad vegetation cover is influenced mainly by temperature, especially near 40 cm ground temperature below the earth surface. NDVI is very sensitive to near 40 cm ground temperature change. Permafrost is widely distributed in the source regions of the Yangtze and Yellow rivers. Its freezing-thawing processes are not only associated with ground temperature change, but also affect soil water content. Permafrost degradation will influence directly alpine vegetation growth in the source regions of the Yangtze and Yellow rivers.