Response Of NDVI To Climate Change In The Growing Season Of Tibetan Plateau

The fragile alpine vegetation in the Tibetan Plateau(TP)is very sensitive to environmental changes,and TP is one of the hotspots for studying the response of vegetation to climate change.The present study lack the detailed description of the response of vegetation of different vegetation types and different elevations to more than three different climatic factors in different periods in the TP.Studies on the lag of vegetation response to climate change are often based on the following two methods.One is the point-based research,which calculates the lag time of vegetation response to climate factors by counting the pixel NDVI value or the mean value of pixel NDVI in a certain range of meteorological stations,and characterizes the response degree of vegetation to climate factors by statistics of multi-point lag time.The other is the face-based research,in which the meteorological data raster map is obtained from the meteorological station data interpolation,and the correlation between the meteorological data raster map and NDVI raster map is analyzed.Finally,the lag time is determined according to the average correlation degree of different time.The first method has high research accuracy,but it depends on the distribution of meteorological stations.The second method can still be studied in places where there are few meteorological stations,but the results ignore the description of the details.Based on modis09a1 data,the NDVI data of vegetation in the TP are inverted.We use time nested series to study the growth trend of different vegetation types.Grey relational analysis and point-by-point analysis were used to study the response degree and response speed of vegetation growth to climatic factors in this area.Finally,the interaction between vegetation and climate in the TP was discussed through the above research,and the spatiotemporal differences of NDVI response to climate factors were analyzed.The main conclusions are as follows:(1)The spatial distribution of NDVI values the growing season of TP shows a trend of decreasing from east to west,and from north to south,with a change rate of-0.13/10°E and-0.3/10°N respectively.(2)In the past 17 years,NDVI of vegetation in the growing season of the TP showed a slight increase trend,with an increase rate of 0.01/10 a.Among them,the NDVI value of vegetation in 15.4% of the study area improved significantly,7.31% of the area improved significantly,2.5% of the area showed significant degradation,and 0.89% of the area showed significant degradation trend.The proportion of the area with the rising trend of vegetation NDVI in the middle and low altitude areas of the TP is higher than that in the high and extremely high altitude.on the whole,the area where the NDVI value of vegetation is increasing in the growing season shows an increasing trend,but the increasing trend of vegetation NDVI tends to moderate in the future.(3)On the whole,the response degree of vegetation to sunshine duration is the highest.Among different vegetation types,meadow,shrub,broad-leaved forest and coniferous forest have the highest response to sunshine duration;grassland and alpine vegetation are more susceptible to air temperature and precipitation;cultivated vegetation has a higher response to precipitation.(4)The lag response of NDVI to climate factors shows that,on the whole,most of the vegetation in the TP has a good correlation with the air temperature in the same period,the lag time of response to precipitation is mostly within 0-1 month,and the lag time of response to relative humidity and sunshine duration is 2-3 months.(5)The strong driving area of NDVI sunshine duration(17.35%)is much larger than that of air temperature driving area(10.26%),precipitation driving area(9.84%)and relative humidity driving area(10.05%),and the vegetation growth in the TP is most closely related to sunshine duration,followed by air temperature and relative humidity,and finally precipitation.