2001-2020年青藏高原草地物候变化遥感监测

Remote Sensing Monitoring of Grassland Phenological Changes in the Qinghai-Tibetan Plateau During 2001-2020

[目的]探究青藏高原草地物候时空变化规律,对于理解高寒生态系统与区域气候之间的相互作用和生态安全屏障保护与建设具有重要的科学意义。[方法]基于2001—2020年MODIS归一化植被指数(NDVI)时序产品,采用非对称高斯函数拟合法和动态阈值法,提取了青藏高原草地NDVI峰值、NDVI峰值期、返青期(SOS)、枯黄期(EOS)和生长季长度(LOS)参数。[结果](1)研究区草地物候的空间分布规律明显,自西向东,草地NDVI峰值增加、峰值期提前、SOS提前、EOS推迟、LOS延长。(2)20年间,青藏高原草地物候年际变化主要表现为SOS呈提前趋势(12.11%的区域显著提前),EOS呈推迟趋势(18.49%的区域显著推迟),LOS呈延长趋势(18.87%的区域显著延长)。(3)青藏高原气温、降水对SOS有1~2个月的滞后效应;气温对EOS有1~2个月的滞后效应,而降水对EOS的滞后效应不明显。考虑滞后效应的条件下,气温是影响草地SOS,EOS年际变化的主导因子。[结论]青藏高原草地物候具有空间异质性,且气温是影响草地物候时空变化的主要因素。

[Objective]Exploring the spatiotemporal variation characteristics of grassland phenology on the Qinghai-Tibetan Plateau is of great scientific significance for the interaction mechanism between alpine ecosystems and regional climate,and the protection and construction of ecological security barrier.[Methods]Based on the MODIS NDVI time series products from 2001 to 2020,the NDVI peak,NDVI peak period,start of growth season(SOS),end of growth season(EOS)and length of growth season(LOS)were extracted by combining with asymmetric Gaussian function fitting method and dynamic threshold method.In addition,the spatiotemporal changes of grassland phenology and its response to climate change were analyzed.[Results](1)The obvious spatial distribution of grassland phenology showed that from west to east,the peak NDVI tended to increase,the NDVI peak period tended to advance,the SOS gradually advanced,the EOS gradually delayed,and the LOS gradually lengthened.(2)During the 20-year period,the interannual variation of grassland phenology over the Qinghai-Tibetan Plateau mainly indicated that the SOS showed an advanced trend(12.11%of the study area were significantly advanced),the EOS showed a delayed trend(18.49%of the study area were significantly delayed),and the LOS showed a lengthened trend(18.87%of the study area were significantly lengthened).(3)The lag time of SOS trend response to temperature and precipitation was 1~2 months over the Qinghai-Tibetan Plateau;the lag time of EOS trend response to temperature was 2 months,the lag effect of precipitation on EOS was not obvious.Considering the lag effect,temperature was the dominant factor affecting the interannual variation of the SOS and EOS.[Conclusion]Grassland phenology on the Qingahi-Tibetan Plateau has spatial heterogeneity,and temperature is the main factor affecting spatiotemporal changes of grassland phenology.