Construction And Application Of Standardized Vegetation Moisture Index In Northeast China

Drought has been a natural disaster affecting human life and social production since ancient times.Plants are one of the important components of the biosphere,connecting the atmosphere,lithosphere,and hydrosphere,and are extremely vulnerable to drought.Global warming is unquestionable.Studying the catastrophic events caused by drought is conducive to effective risk management of drought,promoting the rational use of water resources,and promoting human production and social and economic development.Vegetation moisture is used as an indicator to quantify drought,the influence of atmospheric moisture is overcome,and the influence of atmospheric moisture is overcome by this article.Using vegetation moisture as an indicator to quantify drought,the dry and wet changes in Northeast China at different time scales from 2001 to 2019 The characteristics and the feedback of vegetation after drought are explored in this paper.The MODIS09A1 surface reflectance data from 2001 to 2019 was used.In order to effectively overcome the influence of atmospheric moisture on vegetation moisture monitoring,the near-infrared band(Band 2)and short-wave infrared band(Band 6)were used to calculate the global vegetation index,and Select a suitable probability density function/distribution,and use a standardized method to standardize GVMI to SVMI.The improved Mann-Kendall trend test method was used to analyze the spatio-temporal changes of vegetation moisture in the Northeast;the combination of REOF and k-means clustering method was used to divide the vegetation moisture changes in different time scales and analyze the differences the vegetation type of the district and its response to drought;based on the basic mathematical statistics method to calculate the resistance of vegetation to drought.The specific conclusions are as follows:(1)Compared with the other three-parameter probability density function/distr-ibution,the standardized results using the Log-logistic distribution function all obey the normal distribution,the standard deviation is 0.95-1,the average value is between ± 0.05,and the Log-logistic distribution function is used.The paramete-r estimation is statistically significant;(2)The Northeast China showed a significant drought trend from 2001 to 2019(P<0.05).In terms of seasonal changes,there is a significant drying trend at a rate of-0.4/10 a in winter,and a humidification trend at a rate of 0.14/10 a in spring,which is the only season showing a humidification trend;different time scales in Northeast China before2010 Under the circumstances,the dry and wet changes fluctuate greatly.The summer,autumn and winter of 2012-2019 are generally in a relatively dry period,and the spring is a relatively humid period;(3)The change of dryness and wetness presents the characteristics of wet north and dry south,dry mountain and hilly wet plains,and dry forest wet grassland.The coniferous forest in the north of the Greater Khingan Mountains show a significant moisturization trend on the annual time scale with a trend of 0.6/10 a,while the black soil belt in the northern Songnen Plain and the typical steppe zone of the Xilin Gol Plateau have a trend of-0.83/10 a respectively.The rate of-0.74/10 a shows a significant aridification trend on the annual scale;there are roughly two drier periods in meadow grassland and typical grassland in 2005-2010 and 2015-2019,and the northern and central parts of the Songnen Plain are generally Drought after 2010;(4)The frequency of vegetation drought is high in the west and low in the east.The meadow grassland,typical grassland and dry grassland on the west side of the Greater Khingan Mountains have a higher drought frequency.About 20-40 droughts have occurred in the Da Khingan Mountains and the east during the past 20 years.The number of droughts in mountainous and hilly areas is less than 10;the duration of drought is less than that of forest vegetation(32 d)than grassland and cultivated land(40-56 d),and the drought intensity of meadow grassland and cultivated land in the middle of the plain is less than that of other areas;spatial and temporal changes in performance has to reduce the frequency of droughts in northern forests,the corresponding intensity and duration of droughts have also been reduced;the western prairie area is arid and the high incidence of "disaster area",but in recent years is also showing drought frequency The increasing duration and intensity are decreasing;on the contrary,the meadows and swamps of the Sanjiang Plain tend to have long-term and high-intensity drought events in recent years;(5)The resistance of forests,grasslands and meadows and swamps to drought is obviously different.In terms of space,the resistance of forests,meadows and swamps to drought is higher than that of grasslands,and the level of groundwater level affects the resistance of vegetation to drought.