2000—2018年那曲市植被NDVI变化及气候变化响应

NDVI Change and Its Response to Climate Change in Nag Qu City during 2000-2018

植被覆盖动态变化的监测对区域生态环境保护具有重要意义。本文基于2000-2018年MODIS NDVI产品和地面气象站点观测数据,利用MVC最大值合成法、线性趋势分析法、Hurst指数法分析了那曲市植被NDVI变化趋势,并通过相关性、偏相关性分析法研究不同时间尺度和不同植被类型NDVI变化对气候因子的响应特征。研究表明:近19年来那曲市植被NDVI总体上呈不显著减小趋势,稳定状态的植被所占比重最大,占64. 5%,退化区面积略大于改善区面积,但差距不大。另外,高寒荒漠类、高山植被类和高寒草原类植被呈上升趋势,其中高寒荒漠类植被上升趋势较显著(R^2=0. 52,P <0. 05),其余两类呈微弱的上升趋势;灌木类草地、高寒草甸类和针叶林类植被呈微弱的下降趋势。从可持续性来看,植被NDVI处于不变弱反持续比重最大,占35. 6%。持续退化和弱反持续改善型分别占全市面积的7. 42%和8. 26%,其他4种类型占总面积的13. 69%。从气候特征上看,近年来那曲市以暖湿型气候为主,这种气候特点有利于植被的生长和恢复。水热因素作为植被生长的两个重要因子,在不同时间和空间尺度上对植被生长具有不同的特点,即NDVI与月平均气温和月降水量间存在显著正相关性。

The dynamic monitoring of vegetation coverage plays an important role in the protection of regional ecological environment. Based on NDVI of MODIS products and meteorological observations during 2000-2018,along with analytical methods to be used including MVC maximum synthesis,linear tendency analysis,Hurst index,correlation coefficient and partial correlation coefficient,in this research it studied the distribution of NDVI with different time scales and vegetation types and its corresponding characteristics to the climatic factors in Nag Qu city,Tibet,China. Results showed that NDVI had presented slightly decreasing tendency in the past 19 years. The proportion of stable vegetation occupied the maximum area accounting for 64. 5%. The coverage of degraded vegetation was slightly larger than that of improved vegetation. Furthermore,the distribution of vegetation was different with various types. The vegetation in cold desert,alpine vegetation,and alpine grassland presented increasing tendency,and the tendency was quite obvious for alpine desert( R^2= 0. 52,P < 0. 05) among them,while the vegetation of shrub grassland,alpine meadow,and the coniferous forest was on the decline slightly.Considering the sustainability,continuous degradation and weak anti-continuous improvement areas accounted for7. 42% and 8. 26% of the whole city respectively,while the other four types accounted for 13. 69%. In recent years,climate change exhibited a "warm and humid"trend over Nag Qu city which was beneficial for the growth and improvement of vegetation. As main factors for vegetation growth,water and heat had different influence on the vegetation at various spatial and temporal scale. Namely,the NDVI was closely positive to monthly temperature and precipitation.