Trend Of NDVI And Vegetaion Phenology Change And Response To Climate Change Research In Karst Faulted Basin

As an important ecologically fragile area and ecological safety barrier zone in China,the southwestern karst fault basin is sensitive to changes in hydrothermal conditions.The impact of climate change on the vegetation ecosystem in this area cannot be ignored.The spatial and temporal dynamics of vegetation phenology and its response mechanism to climatic factors in this area are explored,and the driving mechanism of climatic factors on vegetation phenology is revealed,which is especially necessary to protect the stability of ecosystems in this area.In the context of global warming,in view of the special ecological environment characteristics of the southwestern karst fault basin,this study uses the 2001-2016 MODIS data to analyze the spatial and temporal evolution of NDVI and phenological changes in the southwestern karst fault basin.The correlation between temperature and precipitation gives the following main conclusions:(1)During the period of 2001-2016,the annual average temperature of the southwestern karst fault basin increased by 0.33?/10a,and the annual average precipitation decreased gradually with the change rate of-14.34mm/10a;among them,spring,summer and autumn The temperature showed an increasing trend,and the winter temperature showed a downward trend.The precipitation in spring and summer showed a decreasing trend,and the precipitation in autumn and winter showed an increasing trend.The spatial variation trend is reflected in the spatial distribution of the overall pattern of north fast south and slow,and the spatial variation of precipitation trends is obvious.(2)The average NDVI range of the southwestern karst fault basin is between 0.4 and 0.8,and the overall vegetation growth is better.The summer NDVI has a significant decrease of-0.043/10a.The annual average value of NDVI in the study area decreased slightly by-0.012/10a,and the area where NDVI showed a docreasing trend(56.72%)was slightly larger than the area where NDVI showed an increasing trend(43.28%).The area where NDVI increased significantly was mainly concentrated in salt source.County,Xundian County,Xuanwei County and Liupanshui City.(3)The annual average temperature and precipitation have a strong positive correlation with NDVI in most areas of the southwestern karst fault basin.The temperature rises to the eastern Xuanwei City,Liupanshui City,Qiubei County,and Yanyuan County in the north.Vegetation growth has a promoting effect,and the reduction of precipitation has an inhibitory effect on NDVI except Yanyuan County and Muli County.Through the study of the driving factors of NDVI under different soil types,it is found that precipitation has a great effect on the soil surface NDVI of all types of soil.In this study area,the two soil types of yellow soil and brown soil are better vegetation.Growing and developing soil environment.(4)During the period of 2001-2016,the SOS(starting season of the growing season)in the southwestern karst fault basin averaged the first day of the period of 192.41,and the range was mostly concentrated between 170-190 days(from mid-June to early July).EOS(growth season)The final period is 339.31 days on average,and the range is mostly between 300-340 days(from the end of October to the beginning of December).The LOS(length of growing season)is 146.91 days,and the range is mostly 130-160 days.In the past 16 years,SOS occurred.The rate of change was 7.7d/10a,the rate of change of EOS was 10d/10a,and the rate of change of LOS was 2.3d/10a.(5)The effects of meteorological factors in different periods on the vegetation phenology of different location conditions are very different.The annual average temperature increase in the southwestern karst fault basin has a strong postponement effect on SOS in most areas.SOS is more sensitive to annual temperature than precipitation.Both the increase in spring temperature and the decrease in spring rainfall play an important role in the delay of SOS;EOS is not sensitive to annual temperature and precipitation,summer temperature rise,precipitation decrease and winter temperature decrease for EOS The postponement has a strong push;the impact of annual average temperature and precipitation on LOS reflects the spatial differentiation of a large area,such as the surrounding areas of the Jinsha River at the Sichuan-Yunnan border,Panzhihua City,Huidong County,and eastern Yuxi City.The increase in spring temperature and the decrease in precipitation have caused a certain shortening effect on LOS,while the decrease in summer precipitation has extended LOS.The study also found that the vegetation SOS and EOS under different soil types showed great differences,and the responses to climate change were significantly different.