Temporal And Spatial Changes Of Vegetation Phenology And Its Influencing Factors In Yangtze River Delta Urban Agglomerations

The process of urbanization is the most evident form of remaking nature.It significantly changes the hydrothermal environment inside the city and affects the growth of vegetation.On the other hand,the expansion of urbanization is also closely related to regional climate change,which affects the growth process of vegetation.Plant phenology is a display of environment and climate change.The study of urban phenology is helpful for understanding the impact of urbanization on ecosystem.Remote sensing data has stability,objectivity and timeliness,and is widely used in the study of plant phenology.In this study,the Yangtze River Delta region is selected as the research area.Based on remote sensing data,the temporal changes and spatial distribution characteristics of plant phenology(including SOS,EOS,and GSL)were extracted and the effects of human factors and climate factors on vegetation phenology were discussed.Main conclusions are as follows:(1)In the Yangtze River Delta region,the SOS was advanced,the EOS was postponed,and the GSL was extended.The changes in the suburbs are the most significant,and the GSL is prolonged by an average of 1.37 days per year,followed by the rural areas.Only the SOS and the GSL in the urban area show obvious change trends.Compared with the phenological differences between suburbs and rural areas,the phenological differences between urban and rural areas are larger and show a trend of narrowing.(2)Compared with the SOS,the EOS in different cities shows more obvious differences.Along the urban-suburban-rural direction,the phenological differences show a clear gradient phenomenon.Averagely,on the urban-rural gradient,urban SOS 9.6 days in advance and urban EOS delayed by 9.6 days.(3)The difference of plant phenology along the urbanization level is closely related to the land surface temperature.In this direction,it is found that a 1? increase in spring LST led to a 4.3 days advance in SOS;a 1? increase in autumn LST led to a 3.6 days delay of EOS.(4)Among three regions with different levels of urbanization(urban areas,suburbs,and rural areas),there is a higher correlation between the phenological change and human factors in the suburbs;only the SOS in urban areas is significantly correlated with some human factors;Compared with the SOS,the EOS of rural phenology has higher correlation with human factors.Besides,climate is one of the external factors that affect the plant phenology.