| Phenology of vegetation refers to the phenomena of plant germination,leaf spreading,flowering,fruiting,deciduous and so on,which occur in the course of plant growth with seasonal changes.As a member of terrestrial ecosystem,vegetation plays an important role in the global material cycle and energy exchange.Its phenophase can not only reflect seasonal changes,but also reflect the response of terrestrial ecosystem to changes in environmental conditions.Therefore,the study of vegetation phenophase is of great significance to the in-depth study of global climate change and terrestrial ecosystem.Using MCD12Q2 data set and MOD17A3 GPP(Gross Primary Productivity)data from 2001 to 2014,the temporal and spatial characteristics of phenological: SOS(Start of the Season),EOS(End of the Season)and LOS(Length of the Season)changes in temperate regions of China(>30°N)and the impact of phenological changes on GPP through regression analysis and correlation analysis have studied,which enriches the information of vegetation phenology in China and provides a basis for comparative analysis of vegetation phenology from different data sources.Meanwhile,SOS and EOS in the study area are calculated by MOD13A2 NDVI from 2003 to 2008.The results are compared with the vegetation phenology observed on the ground,and the daily temperature data are used to correct the calculation results to make them closer to the data observed on the ground.The main conclusions are as follows:(1)In terms of time analysis,results show that the average and standard deviation of SOS,EOS and LOS from 2001 to 2014 are 121±10,270±12 and 153±12 days,respectively.The overall SOS showed an advance trend(r=-0.36,p=0.21),EOS showed a lagging trend(r=0.41,p=0.15)and LOS showed a growth trend(r=0.51,p=0.06),but the correlation between annual average LOS and GPP was significant(r=0.74,p=0.0025).(2)In terms of spatial distribution analysis,95.2% of SOS appeared in 71-153 days,98.3% of EOS in 253-301 days,and LOS in 18-220 days.The annual average values of LOS and GPP showed an increased trend from northwest to southeast,and the annual average GPP values were larger in the areas with long growing season.(3)The interannual change rate of phenological period showed that SOS and EOS in the study areas with significant interannual change of vegetation phenological period showed an earlier trend,while LOS showed a shorter trend during 2001-2014.Regions with significant interannual variation(p<0.05)of SOS,EOS and LOS are 13%,21% and 13.2%,respectively.(4)The areas with significant correlation between vegetation phenophase and GPP only accounted for a small proportion in the study area.Regions of significant correlation(p<0.05)of SOS,EOS and LOS to GPP account for 8.31%,9.33% and 8.72% of the study area.The correlation between vegetation phenophase and GPP was mainly moderate(P<0.05,0.5<|r|<0.8).The spatial distribution of correlation between EOS,LOS and GPP is similar.The change of vegetation phenophase will affect GPP,but the increase of LOS in different geographical locations will affect GPP in different directions and degrees,SOS and EOS are also the same.The area with significant change of vegetation phenophase(p<0.05)occupies only 4.29% in the study area.(5)The correction of vegetation growth start date under single temperature condition is better than that under multi-temperature condition.The correction of vegetation growth start date can be made by using temperature.In this paper,the SOS and EOS observed by satellite are corrected by using the maximum daily temperature by establishing a regression model.The starting date of vegetation growth after model correction is more evenly distributed on both sides of y=x than before.Compared with before correction,MRE of SOS decreased from 38.85% to 13.09%,RMSE from 55.24 to 12.44 d.RE of EOS decreased from 16.43% to 6.29%,RMSE from 51.5 to 22.64d. |
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