Zhang Jiahua, Yao Fengmei, Zheng Lingyun, Yang Limin
Laboratory for Remote Sensing and Climate Information Sciences (LRSCIS),Chinese Academy of Meteorological Sciences, Beijing, 100081, China.
College of Earth Sciences, The Graduate University of the Chinese Academy of Sciences, Beijing, 100049, China.
Sensors (Basel). 2007 Dec 17;7(12):3312-3328. doi: 10.3390/s7123312.
The grassland ecosystem in the Northern-Tibet Plateau (NTP) of China is verysensitive to weather and climate conditions of the region. In this study, we investigate thespatial and temporal variations of the grassland ecosystem in the NTP using theNOAA/AVHRR ten-day maximum NDVI composite data of 1981-2001. The relationshipsamong Vegetation Peak-Normalized Difference Vegetation Index (VP-NDVI) and climatevariables were quantified for six counties within the NTP. The notable and unevenalterations of the grassland in response to variation of climate and human impact in theNTP were revealed. Over the last two decades of the 20th century, the maximum greennessof the grassland has exhibited high increase, slight increase, no-change, slight decrease andhigh decrease, each occupies 0.27%, 8.71%, 77.27%, 13.06% and 0.69% of the total area ofthe NTP, respectively. A remarkable increase (decrease) in VP-NDVI occurred in thecentral-eastern (eastern) NTP whereas little change was observed in the western andnorthwestern NTP. A strong negative relationship between VP-NDVI and ET0 was foundin sub-frigid, semi-arid and frigid- arid regions of the NTP (i.e., Nakchu, Shantsa, Palgonand Amdo counties), suggesting that the ET0 is one limiting factor affecting grasslanddegradation. In the temperate-humid, sub-frigid and sub-humid regions of the NTP (Chaliand Sokshan counties), a significant inverse correlation between VP-NDVI and populationindicates that human activities have adversely affected the grassland condition as waspreviously reported in the literature. Results from this research suggest that the alterationand degradation of the grassland in the lower altitude of the NTP over the last two decades of the 20th century are likely caused by variations of climate and anthropogenic activities.
中国青藏高原北部的草原生态系统对该地区的天气和气候条件非常敏感。在本研究中，我们利用1981 - 2001年美国国家海洋和大气管理局（NOAA）/高级甚高分辨率辐射计（AVHRR）的旬最大归一化植被指数（NDVI）合成数据，研究了青藏高原北部草原生态系统的时空变化。对青藏高原北部六个县的植被峰值归一化植被指数（VP - NDVI）与气候变量之间的关系进行了量化。揭示了青藏高原北部草原对气候和人类影响变化的显著且不均衡的变化。在20世纪的最后二十年中，草原的最大绿度呈现出高度增加、轻微增加、无变化、轻微下降和高度下降的情况，分别占青藏高原总面积的0.27%、8.71%、77.27%、13.06%和0.69%。在青藏高原中东部（东部）VP - NDVI出现显著增加（减少），而在青藏高原西部和西北部则变化不大。在青藏高原的亚寒带、半干旱和寒旱地区（即那曲、申扎、巴青和安多县），发现VP - NDVI与潜在蒸散（ET0）之间存在很强的负相关关系，这表明ET0是影响草原退化的一个限制因素。在青藏高原的温带湿润、亚寒带和亚湿润地区（察雅和索县），VP - NDVI与人口之间存在显著的负相关关系，这表明人类活动如文献中先前报道的那样对草原状况产生了不利影响。本研究结果表明，20世纪最后二十年青藏高原较低海拔地区草原的变化和退化可能是由气候和人为活动的变化引起的。
