Analysis Of Vegetation Phenology Changes And Its Influencing Factors In Wuhan City

Vegetation phenology is of great significance for studying the relationship between climate change and vegetation,which is an important index indicating vegetation growth.Urbanization is one of the main driver of global changing,with great impact on regional climate.Therefore,it is of great significance to study urban vegetation phenology.Vegetation of urban areas is usually scattered,so it is difficult to finely identify and analyze vegetation using the low-resolution remote sensing images of kilometer-level,while the remote sensing data of 10-meter resolution are difficult to meet the requirements of phenological analysis in terms of time resolution.To this end,this paper adopted a spatio-temporal information fusion method based on non-local means filter to generate time series of remote sensing images with high spatial resolution and high temporal resolution.Based on the fused data,this paper studied the spatial and temporal patterns of vegetation phenology in Wuhan City,and explored the influencing factors.The main contents of this paper are as follows:(1)Data of 30-meter resolution were generated by spatio-temporal method.A spatiotemporal information fusion method based on non-local means filter was adopted to generate the surface reflectance image time series with spatial resolution of 30 meters and time resolution of 8 days in Wuhan City,followed by band math to obtain the Enhanced Vegetation Index(EVI)time series.Moving weighted harmonic analysis method was used to reconstruct EVI time series,in order to eliminate noises caused by cloud,rain,snow and sensor component failures,and dynamic threshold method was adopted to extract vegetation phenology of Wuhan City from 2006 to 2014.(2)Based on the phenological results,the spatial characteristic and temporal variation of vegetation phenology in Wuhan were analyzed.The results showed that the spatial characteristics of start of season(SOS)in Wuhan from the urban to the suburbs gradually delayed,end of season(EOS)gradually advanced,and the length of season(LOS)gradually extended.That is to say,there were earlier SOS,later EOS and longer LOS in urban areas than suburbs.As time passed,the overall trend of SOS advancing,EOS delaying,and LOS extending was presented.(3)Based on the phenological extraction results,influencing factors of vegetation phenology in Wuhan were explored.This paper focused on the relationship between vegetation phenology and meteorological factors,including temperature,daily temperature difference and precipitation.The results showed that the correlation between vegetation phenology and average temperature was not significant,but EOS and LOS were significantly affected by the average annual temperature difference.As one degree of the average annual temperature difference rose,EOS delayed by about 12 days,and LOS extended by about 16 days.Precipitation mainly affects SOS and LOS.As every 100 mm of precipitation increased,SOS advanced by 5 days,and LOS extended by about 9 days.