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Spatiotemporal Variation Of Soil Moisture And Its Effect On Grassland Vegetation Phenology In The Mongolian Plateau

Posted on:2022-10-05Degree:MasterType:Thesis
Country:ChinaCandidate:J X WangFull Text:PDF
GTID:2493306485960579Subject:Cartography and Geographic Information System
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As an important part of the global energy cycle,soil moisture is a key parameter describing the exchange of moisture and energy between land and atmosphere.It has a major impact on the earth’s water cycle,energy balance and climate change.Soil moisture can also provide an important source of water and energy for the growth and development of plants,and the phenological characteristics of vegetation will also provide corresponding feedback to adapt to changes in soil moisture.Therefore,based on the GLDAS soil moisture data,GIMMS NDVI and MODIS NDVI data,and meteorological data from 1982 to 2019,this paper uses linear regression analysis,trend analysis,cumulative Logistic curve curvature extreme value method and correlation analysis to analyze the soil moisture time and space in the Mongolian Plateau.Changes and their impact on grassland vegetation phenology were studied,and the following conclusions were obtained:(1)From 1982 to 2019,the soil moisture of 0~10cm(SM1)in the Mongolian Plateau showed an insignificant increase at a rate of 0.002 m~3/m~3/10 a,and the mutation time occurred around 2012;10~40cm(SM2)soil The rate of water change is-0.004 m~3/m~3/10 a,with a significant decreasing trend and abrupt changes around 1996.In spring and winter,SM1 soil moisture showed a significant increasing trend;in summer and autumn,SM1 soil moisture showed an insignificant decreasing trend.The soil moisture of SM2 showed a decreasing trend in different seasons.In addition,the annual variation of soil moisture in the deep layer is smaller than that of the shallow layer.The annual average soil moisture at different depths shows a gradual decrease in space from northeast to southwest and presents a pattern of relatively high soil moisture values on the periphery of the plateau and relatively low internal soil moisture values.The soil moisture of SM1 and SM2 have good consistency in spatial distribution.The area of SM1 showing an increasing trend accounts for about 71.89%,including the Altai Mountains,the Yinshan Mountains and the Daxingan Mountains in the east.The area showing a decreasing trend of SM2 accounts for about 66.13%,distributed in the northern part of Hangai Mountain,Sayan Mountains and Horqin Sandy Land.(2)The vegetation return period(SOS)of the Mongolian Plateau from 1982 to 2019 was mainly concentrated from late April to mid-May,accounting for about 70.41% of the study area.Over the years,SOS has shown an advance trend at a rate of 1.09 d/10 a,accounting for about80.23%.On the whole,the emergence time of vegetation SOS is desert grassland,meadow grassland,typical grassland and alpine grassland.The yellow vegetation period(EOS)is mainly concentrated in early October to mid-October,accounting for about 90.21% of the total area.The annual average EOS shows an early trend at a rate of 0.32 d/10 a,and the proportions of regions showing an early and late trend spatially are roughly similar,about 51.27% and 48.73%,respectively.The emergence time of vegetation EOS is alpine grassland,typical grassland,meadow grassland and desert grassland in sequence.The area where the vegetation growth period(LOS)is maintained for 130 to 170 days accounts for about 66.46%.The annual average LOS showed a prolonged trend at a rate of 0.67 d/10a(about 70.81%).Overall,the LOS maintenance length is desert steppe,meadow steppe,typical steppe and alpine grassland in order from long to short.(3)The annual average soil moisture of the Mongolian Plateau is mainly positively correlated with vegetation SOS and EOS.Areas with a positive correlation between SM1 and SOS include Gobi Altai Mountains and Horqin Sandy Land.The regions showing a positive correlation between SM1 and EOS are distributed in most of the central and western parts of the plateau.The spatial distribution of SM2 and SM1 are in good agreement.SM1 and LOS are mainly negatively correlated,and the negatively correlated areas are distributed in most areas of the central and western plateau.However,SM2 and LOS are mainly positively correlated,and they are positively correlated in Gobi Altai Mountains,southern Hangai Mountain and western Daxinganling.SOS and EOS of most vegetation in the study area had obvious lag effect on soil moisture,and the correlation with the soil moisture in the 1 ~ 3 months before the season is relatively significant,and the lag phenomenon is more significant.Among them,the effect of soil moisture of SM2 on the SOS of different grassland vegetation is different than that of SM1,and the effect of soil moisture of SM2 on the EOS of different grassland vegetation is similar to that of SM1.In contrast,the hysteresis of SOS and EOS of different grassland vegetation in response to different layers of soil moisture are also significantly different.
Keywords/Search Tags:Mongolian Plateau, soil moisture, vegetation phenology, correlation analysis, time lag correlation analysis
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