Spatial-temporal Variation And Climate Response Of Vegetation Phenology In Western Sichuan Plateau During 2001?2015

Vegetation phenology is the result of the interaction between vegetation and the natural environment.The change of vegetation growth rhythm can cause the change of ecosystem material cycle(such as water,carbon)and biodiversity.Vegetation phenology as an important indicator of climate change is obviously affected by climate change,and can directly reflect the effect of climate change on the ecological environment.Based on climate data and MOD09Q1 NDVI form 2001 to2015,this article studies the distribution and change trend of vegetation phenology(SOG,Start of growth season;EOG,End of growth season;LOG,Long of growth season)in the Western Sichuan Plateau by dynamic threshold method.Then the correlation between phenological change and climate change is analyzed.The research results summarize the relevance between vegetation growth status and climate change.It is of great significance in investigation of ecological environment,protection of water sources,and guiding the restoration of the ecological environment.The main conclusions are as follows:(1)The SOG shows volatility advance with the average annual value of 123.29 th days(in early May)and the tendency rate of-4d/15 a.The EOG shows volatility advance with the average annual value of 299.91 th days(in late October)and the tendency rate of 6.3d/15 a.The LOG shows volatility advance with the average annual value of 176.68 days(five and a half months)and the tendency rate of 10.05 d/15 a.In the past 15 years,the ecosystem in Western Sichuan Plateau has a good trend because of the advance of SOG,the delay of EOG,the extension of LOG.The spatial distribution of vegetation phenology in the study area is closely related to the elevation.With the increase of 1000 m,the SOG is delayed for 16 days,the EOG is advanced by 16 days and the LOG is shortened by 29 days.(2)The distribution of mean vegetation phenology in Western Sichuan Plateau is divided into three units,the eastern Valley,the Ruoergai Plateau(or with the same elevation)and the area with elevation above 4000 m.In the valley of Minjing,Daduhe and Baishuijiang,the SOG is 75th~for 110 th days,the EOG is 315th~ for 335 th days,the LOG is from 210 days(seven months)to 255 days(eight months).In the Ruoergai Plateau,the SOG is 110th~125th days,the EOG is 300th~ for 315 th days,the LOG is from 180 days(seven months)to 210 days(eight months).In the region which elevation is above 4000 m,the SOG is after the 125 th days,the EOG is before the 315 th days,the LOG is shorter than 180 days(seven months).(3)In Ngawa Prefecture,the SOG advances prominently,and the EOG delays significantly.But there is no obvious change trend of SOG and EOG in the northwest of Garzê Prefecture,its LOG shows an extension.In addition to the northwestern region of Garzê Prefecture,the SOG shows an early trend,the EOG shows a delayed trend,and the growth trend is less than Ngawa Prefecture.(4)In the background of global warming,the air temperature and precipitation of each stage of vegetation phenology show a growing trend in Western Sichuan Plateau during 2001~2014.the air temperature and precipitation rate in SOG stage are 0.48?/10 a and 4.8mm/10 a,the air temperature and precipitation rate in EOG stage are 0.10?/10 a and 2.1mm/10 a,the air temperature and precipitation rate in LOG are 0.45?/10 a and 22.8mm/10 a respectively.(5)The correlation of the SOG and EOG in the Western Sichuan Plateau is significantly correlated with the air temperature,and is significantly higher than that of the precipitation.The correlation between LOG and air temperature is weak,the degree of significance is low,but the correlation of precipitation is obvious.(6)The multiple correlations between SOG/EOG and air temperature/ precipitation in Western Sichuan Plateau have a larger distribution difference.In the northern of Western Sichuan Plateau except Ruoergai plateau,the complex correlation coefficient between EOG and air temperature-precipitation is small.But the correlation coefficient is greater than that in the south region.The complex correlation coefficient between LOG and air temperature-precipitation is generally small.