A Study On The Relationship Between NDVI And Plateau Climate On The Qinghai-Tibet Plateau

This article uses the MODIS MOD13Q1 NDVI meteorological satellite remote sensing data and the Tibetan Plateau site observation data from 2000 to 2018,based on the research of ecological geographical division which is "pieces" way of thinking,using empirical orthogonal function decomposition,kriging interpolation,linear regression,Mann-Kendall Test,Moving t-Test and correlation analysis,temporal and spatial variation characteristics of NDVI and different vegetation types are studied in the region of plateau in recent years(including alpine grassland,alpine meadow,alpine desert and coniferous forest).The changes of NDVI and mutation phenomenon of it are researched.And then we analyzes the correlation,which is occurred between different kinds of vegetation NDVI change and temperature,precipitation changes,and get the following conclusions:The plateau vegetation mainly shows the gradient from southeast to northwest and zonal distribution,and gradually decreases according to the gradient.The spatial and temporal variation of NDVI in winter,spring and summer of the plateau result in the deflection of the spatial distribution pattern of the first mode and its time coefficient,in 2009,2010 and 2011,respectively.The temporal variation of NDVI in autumn is basically similar to that in spring,but its spatial distribution has little change.From the perspective of the plateau as a whole,the spatial and temporal variation trend of vegetation is in the direction of preference.The annual variation of plateau NDVI has regional differences in ecological geography.NDVI of alpine meadow shows a significant decreasing trend.Since 2015,the increase rate of NDVI of alpine grassland has changed significantly.Alpine desert NDVI increases significantly in recent years.The annual growth of coniferous forest is stable in recent years.Mutation test shows that the decreasing trend of the annual mean value of NDVI of alpine meadow in recent years is a mutation phenomenon,which started from 2011.Annual mean value of NDVI of the alpine steppe changed only in 2007.The spatial distribution of summer temperature on plateau is a "warming-cold-warm" pattern from south to north.Vegetation cover of alpine meadow can significantly affect its summer temperature only in summer,especially the cooling effect of vegetation.Vegetation cover in spring,statistically speaking,can stabilize the temperature in summer to some extent.The relationship between summer temperature and spring NDVI is closest.The change of summer temperature of alpine desert has a strong response to the growth of vegetation cover in the same period.The complex geographical conditions of coniferous forest area may be one of the reasons for the positive correlation between summer temperature and vegetation change.The spring precipitation in plateau region is generally rare,and the precipitation is mostly concentrated on the subtropical region,south of 30°N,southeast of the plateau.According to the results of EOF analysis,the western part of the plateau has more spring precipitation in recent years,while the eastern part is drought.Growth change of alpine meadow in June has a certain lag in response to precipitation change in region,and May is the most significant month.The precipitation of the alpine steppe is positively correlated with NDVI but overall weak.The response of vegetation of the alpine desert region to precipitation in June is also lagging,but also weak,and it is not correlated with the precipitation in the same period after the control of the temperature variable in the same period.In coniferous forest area,the response of vegetation growth in June to precipitation is synchronism and two-month lag.The influence of spring precipitation on vegetation declines to a certain extent in summer,especially in coniferous forest areas.Vegetation growth in alpine desert areas has a continuous response to spring precipitation in the whole summer.The relationship between NDVI and spring precipitation of alpine meadow and alpine grassland in summer has little change,compared with that in June,and NDVI in summer increases with the increase of spring precipitation on average.Correlation analysis and partial correlation analysis showed that,on the one hand,the summer temperature of the plateau is generally positively correlated with the NDVI of the previous two seasons,but it is weak except for the strong correlation of coniferous forest.Temperature in summer of plateau,on the other hand,does has a certain degree of negative correlation with NDVI change,but the impact of precipitation on the temperature can't be ignored at the same time,in fact,after the variable control of the same period precipitation in summer,the correlation between vegetation and summer temperature are still weak.According to the relationship between spring precipitation and NDVI in June and summer,the influence of spring precipitation on alpine meadow is weakened from June to the whole summer.The influence of spring precipitation on NDVI in alpine grassland and alpine desert is stable from June to the whole summer.There is no correlation between summer NDVI and spring precipitation in coniferous forest.In combination with the correlation between NDVI and the temperature of the same period of the alpine desert in summer,it can be judged that,among the influencing factors of vegetation growth in the alpine desert in summer,if temperature and precipitation are compared,the influence of temperature should be taken as the leading factor.