Tibetan Plateau’s Vegetation Phenology’ Variations And The Analysis Its Driving Factors

Analyses on the vegetation phenology and its variation in Tibetan Plateau are ofscientific importance to reveal the changes of the Earth’s third pole and its ecologicalresponse to global climate change.In this paper, after filtering GIMMS-NDVI vegetation remote sensing databaseusing standard deviation and Savitzky-Golay methods in turn, we quantitativelyanalyze the phenology of vegetation coverage in Tibetan Plateau and its variationfrom1982to2006. The results showed that：1. From May to early June, the eastern of the plateau begin to enter the growingseason, which is earlier than the other plateau places, and the central region growingseason start time is about in middle and late June, whereas the northwest of theplateau is about in late June to early July. The end time of the growing seasonpostpone from the north to the south. Growing seasons in the northwest, north-centraland northeastern will be end in early September, yet it would be later in the south andwest. The lengths of the vegetation growing seasons gradually shorten from thesoutheast to the northwest of the Plateau. The length of growing season in thesoutheast is more than125days, and the length of the central region is about96to111days, whereas the growing season length is about80to96days in most of thenorthwest and northeast. The peak of vegetation growing time in most plateau regionsconcentrate from late July to early August. Absolute and relative growths ofvegetation significantly decrease from the east to the west. The start growing seasonsin most plateau places were ahead from1982to2006. The start growing seasons inthe east and southeast have been ahead at5d/25yr, and the start growing seasonsdelayed at9.4d/25yr are mainly distributed in the central region of the plateau. Theend of the growing seasons were postponed at about12.5d/25yr accounting for71.66%area, mainly located in southeast of the plateau, while in the center and parts of thenortheast, the end time is ahead at about9.8d/25yr. There is an increasing trend withabsolute vegetation growth in the center, southwest and part of the northeast region from1982to2006, while the decreasing trends in parts of the eastern, southeasternand western. There is positive trend from1982to2006with relative vegetationgrowth in the center-western and southwestern regions, while negative trend in thesoutheastern, eastern, northeastern and northwestern regions have.2. The vegetation of the Tibetan Plateau is highly influenced by the rainfall. Theareas which have pole-strength correlation between NDVI and rainfall account for75.1%of the plateau, mostly situated in center and parts of the east and southwest, theareas which have. Strong correlation account for10.3%of the plateau, and the areashaving moderate correlation account for7.1%, whereas the areas having weakcorrelation are merely distributed in the northwest of the Tibetan Plateau and accountfor7.6%.3. The start of the growing seasons is gradually later with the increasingelevation. The earliest start of the growing seasons is30d in advance than that of thelatest. The end of the growing seasons is gradually later with the increasing elevation.The earliest end of the growing seasons is25d in advance than that of the latest. Thelength of the growing seasons is also gradually later with the increasing elevation. Thelongest length of the growing seasons is25d longer than that of the shortest.4. The correlation between NDVI of the Tibetan Plateau and temperaturebecomes weak from southeast to northwest of the Tibetan Plateau, and the areas withstrong correlation account for72.56%.Findings of the research may have a broad implication in understanding theclimate change of the Tibetan Plateau and assessing how vegetation responses to theclimate change.