Spatial Variation Of Vegetation Phenology Along The Urban-rural Gradient In Provincial Capitals In China And Its Influencing Factors

Vegetation phenology,as the "language" of nature and the "diagnostic fingerprint" of global change,had undergone significant changes under global warming.As the center of human social and economic activities,the city's heat island effect continued to increase with the acceleration of urbanization,causing obvious changes in local hydrothermal conditions,which in turn affected the variation pattern of vegetation phenology in urban and rural areas.Therefore,studying the dynamic variation patterns of vegetation phenology along the urban-rural gradient and its response mechanism is of great significance to deeply understand the relationship'between the urban environment and vegetation phenology.In this study,the Savitzky-Golay(S-G)filtering method was used to reconstruct time-series MODIS enhanced vegetation index(EVI)data in 31 provincial capital cities and the surrounding rural areas of China from 2001 to 2018.The dynamic threshold method was used to extract the vegetation phenological parameter:the start of growth season(SOS)and the end of growth season(EOS).And combined with MOD11A2 Land Surface Temperature(LST)from 2001—2018,Globaland30 production in 2010 and Artificial Impermeable Surface data in 2010,we analyzed the variation pattern of vegetation phenology along the urban-rural gradient and its response mechanism.Concluded as follow:(1)From 2001 to 2018,the SOS of 31 provincial capitals and surrounding rural areas in China showed an advancing trend,and the SOS showed a delayed trend;In terms of spatial distribution,the cities with earlier SOS and later EOS were mainly distributed in the middle and low latitudes and low elevations in the central and eastern plains.Cities with later SOS and earlier EOS were mainly distributed in the middle and high latitudes and high altitudes in northeast and western regions.(2)The SOS was earlier in urban areas than that in rural areas,and showed a delayed trend along the urban-rural gradient;The EOS was later in urban areas than that in rural areas,and showed an advancing trend along the urban-rural gradient;And the closer to the city,the greater variation to the phenology.The mean LST of spring and autumn showed a delayed trend with the increase of distance from the city and the closer to the city,the greater degree to the mean LST.The vegetation phenology was closely related to the LST.Specifically,for every 1? increased in spring LST and autumn LST,the SOS advanced 2.11 days,the EOS delayed 1.38 days.What's more,the variation pattern of vegetation phenology and its relationship to LST were quite different among the different cities.(3)The variation patterns of phenology of different vegetation types and their responses to LST were quite different.The SOS of cities in the main winter wheat producing areas were advanced with the increase of distance from the city,and there was a significant positive correlation with the winter LST.The SOS of cities in the main spring wheat and rice producing areas were delayed with the increase of distance from the city,and there were significant negative correlations with the spring LST.(4)The vegetation phenology along the urban-rural gradient showed an significant relationship to latitude.As the latitude moved to the north,the SOS tended to advance,and the EOS tended to delay.Vegetation phenology with the expansion of artificial impermeable surface had no significant change.