黄河源区植被覆盖度对气温和降水的响应研究

Response of vegetation cover to temperature and precipitation in the source region of the Yellow River

本文基于1982-2006年NOAA/AVHRR NDVI和2000-2012年MODIS NDVI两种遥感植被数据以及同期站点的月平均气温和降水资料,通过对重叠观测时期的数据建立映射关系,对NOAA/AVHRR NDVI数据延长插补,分析黄河源区1982-2012年植被的时空变化特征及其对气候变化的响应。结果表明,黄河源区植被覆盖度呈由东南向西北递减的分布格局;海拔在3 000m以下和4 500m以上地区植被覆盖度相对较差,3 000~4 500m地区植被覆盖度相对较好;植被覆盖度在时间变化上呈增加趋势,但在2000年出现突变点,2000年之后增加速率约为之前的2倍;植被覆盖在整体增加的背景下,也存在零星的退化现象,而在西部高海拔和北部较干旱的低植被覆盖度区域植被覆盖的增加仍存在着较大的年际波动,并不稳定;相对于降水,研究区的植被覆盖对气温变化的响应更为敏感,属于热量限制型生态区。

The source region of the Yellow River is located in the hinterland of the Qinghai-Tibet Plateau. The evolution of its alpine vegetation system not only determines the local ecological environment and livestock production,but also significantly influences the ecological safety of the Yellow River basin. Under the influence of climate change and human activities,grassland degradation over upstream headwaters of the Yellow River is increasingly serious. Examining the spatial-temporal characteristics of vegetation cover and its response to climate change in the study area is important for understanding vegetation ecology and changes in water yield across the Tibetan Plateau. Here,based on NOAA/AVHRR NDVI(1982-2006) and MODIS NDVI(2000-2012),monthly air temperature and precipitation of stations,spatial-temporal characteristics of vegetation cover and its response to climate change were investigated in the study area. To analyze the long time series of vegetation variation in the study area,NOAA/AVHRR NDVI were extended by a correction algorithm based on the two kinds of data sets during the overlapping period(2000-2006). The results show that vegetation cover decreased from the southeast to the northwest of the study area. Vegetation cover was poor in areas where elevation was lower than 3000 m and higher than 4 500 m,but better between 3 000 m and 4 500 m. Annual vegetation cover revealed an increasing trend from 1982-2012 but there was an abrupt point in 2000,and the increasing rate after 2000 was about two times before. Vegetation cover change varied in different regions. On the whole,vegetation cover increased from 1982 to 2012 but there was also sporadic degradation. In low vegetation cover regions mainly located in the western high altitude regions and northern arid regions,vegetation cover increases were characterized by large interannual fluctuations. The results of correlation analysis between vegetation cover and climate factors showed vegetation cover was more sensitive to temperature compared with precipitation in the growing season. This indicates that the study area is a typical calorie restriction ecological region.