Vegetation Phenological Variation and Its Response to Climate Changes in Zhejiang Province

In order to understand the vegetation phenological variation of Zhejiang Province and further improve the vegetation response to climate change mechanism,the vegetation phonological variation and relationship with the climate factors were deeply analyzed based on the reconstructed MODIS NDVI time-series using the improved Savitzky-Golay algorithm,the vegetation growth condition was retrieved,and the vegetation phenological metrics(the beginning data,the ending data and length of growing season) were extracted adopting the piecewise polynomial fitting and dynamic threshold method,the vegetation phenology interannual variation trend and its spatial pattern were analyzed,the relationship between the vegetation changes and the climate variations were discussed combined with the meteorological data.The results showed that the vegetation cover expressed slowly decreasing trend,while the length of growth season was slightly extended.The vegetation growing season was from late March to mid November,and the average length of growing season was about 222 days.In the past 10 years,the beginning time of growth season expressed the advance trend,but not significant,and the ending time was significantly delayed.The length of growing season was extended,about 7 days every 10 years.The spatial pattern of the begining time of growing season was delayed from north to south,the ending time was relatively concentrated in November,vegetation growing season of extended area was similar to the shortened area,about 32.40% and 31.88% of the effective pixel respectively.The correlation analysis of phenological metrics and climate factors indicated that heat supply in winter is the important factor for vegetation growth,and the increased cumulative temperature could prompt the start of vegetation growing season.The end of the growing season was positively related with mean temperature while precipitation and humid index were negatively correlated,but not significant,from the view of the month and seasonal scale,the humidity in autumn affected larger on the ending time of growing season.