青藏高原植被覆盖时空变化及其对气候因子的响应

研究青藏高原植被覆盖时空分布特征对加深气候变化的认识及生态环境保护具有重要的生态价值和现实意义。利用2000—2016年MODIS NDVI 1km/月分辨率数据以及气象观测数据,采用最大合成法、趋势性分析以及相关分析方法,探讨了不同时间尺度青藏高原地区NDVI的分布特征及其与降水、气温的关系。结果表明:(1)青藏高原东南部植被状况明显好于西北部,植被覆盖的分布格局与区域水热条件的时空分布保持了较好的一致性;近17年来青藏高原植被覆盖改善的地区要比退化的地区面积大,严重退化的区域主要位于青藏高原西南部;青藏高原NDVI值在2000—2016年呈幅度较小的增加趋势。(2)除夏季降水量外,研究时段内其他季节降水量均呈增加趋势;气温均呈增加趋势,尤其以春季增加最为显著,整体上青藏高原气候呈现"暖湿化"趋势。总体上年降水量与年最大合成NDVI呈较好的正相关;年平均气温与年最大合成NDVI在高原东南部呈正相关,西南部呈负相关。降水量和热量条件均是高原植被生长的影响因素,降水与植被覆盖的影响较气温密切。

Spatio-temporal variation of vegetation coverage over the Tibetan Plateau and its responses to climatic factors

The study of the spatio-temporal distribution of vegetation over the Tibetan Plateau has an important ecological value and practical significance for increased understanding of climate change and ecological environmental protection. Using the monthly normalized difference vegetation index(NDVI) with 1km resolution, determined using the moderate-resolution imaging spectrometer (MODIS), from 2000 to 2016, and meteorological observations, this study analyzed the distribution of the NDVI over different time scales and its relationship with precipitation and temperature over the Tibetan Plateau based on maximum value composites (MVC), linear trends, and correlation analysis method. The results showed that:1) Vegetation status in the southeastern part of the plateau was healthy than that in the northwest. The distribution pattern of the vegetation was consistent with the spatio-temporal distribution of the regional hydrothermal condition. The coverage area of improved vegetation was larger than the areas with degraded vegetation over the past 17 years, and serious degradation areas were mainly situated in the southwestern part of the plateau. The NDVI exhibited an increasing variation tendency with small amplitudes from 2000 to 2016 over the Tibetan Plateau.2) Seasonal precipitation showed an increasing tendency during the study period except in summer, while seasonal temperature presented an increasing trend, with the temperature in spring increasing at the highest rate. Generally, climate change exhibited a "warm and humid" variation trend over the plateau. Annual precipitation was positively correlated with the annual maximum NDVI. Mean annual temperature was positively correlated with the NDVI in the southeastern plateau, and showed an inverse relationship with the NDVI in the southwestern part. Both precipitation and heat conditions affected vegetation growth, and the effect of precipitation on the vegetation was more significant than that of temperature.