Study On The Variation Of Snow Cover And Its Impact On Grassland Vegetation Phenology In Mongolia Plateau

In the context of global warming,the area of snow in the northern hemisphere shows a decreasing trend,while in arid and semi-arid areas where precipitation is scarce,snow melting is an important source of water.Snow can prevent frostbite from vegetation and directly or indirectly affect the greening,growth and productivity of grassland vegetation.In this paper,the Mongolian Plateau is used as the research area.The MODIS data from 2000 to 2017 is used to extract the snow cover and phenological information of the Mongolian plateau and analyze the temporal and spatial characteristics of snow cover and phenology.On this basis,the correlation analysis method and grey correlation analysis method are used to study the effects of snow on different types of grassland vegetation phenology.The main conclusions are as follows:(1)From 2000 to 2017,Snow Cover Fraction(SCF),Snow Cover Duration(SCD)and Snow Cover Albedo(SAL)of Mongolian Plateau showed a decreasing trend,and Snow Cover Onset Date(SCOD)and Snow Cover End Date(SCED)mainly showed an early trend.However,the SCF and SCD of the Hulunbeier Plateau in the eastern Mongolian Plateau and the Xilingol Plateau in the southeast showed an increasing trend.From 2000 to 2017,the SCF of Mongolian Plateau is between 30% and 50%.The average SCF of the Mongolian Altai Mountains and Hangay Uul above 2000 m is the highest(over 60%)and the average SCD is the longest(more than 120 days).The desert and Gobi regions of the Alxa Plateau have the lowest average SCF(less than 5%)and the average SCD is the shortest.SCF was the highest in January of the following year(46.26%);SCF was the highest in 2002(36.83%);in 2014,SCF was the lowest(21.55%).SCOD is advanced from southwest to north;it first appeared in September,distributed in the Mongolian Altai Mountains and Sayan Mountains;the latest appeared in January of the following year,distributed in the Alxa Plateau.SCED was postponed from southwest to north;it first appeared in January of the following year,scattered in some areas of Alxa Plateau;at the latest in April of the following year,mainly distributed in Mongolian Altai Mountains,Hangay Uul,Sayan Mountains,Kent Mountain and Da Hinggan Mountains and Hulunbeier Part of the plateau.SAL has a distribution law that decreases from north to southeast and southwest.(2)From 2001 to 2017,NDVI and Length of growing Season(LOS)of Mongolian plateau showed a trend of growth,while Start of growing Season(SOS)and End of the growing Season(EOS)showed an early trend.From 2001 to 2017,the NDVI in the southwestern part of the Mongolian Plateau was small,and the NDVI in the northern and eastern regions was large.SOS concentrated in mid-April to mid-May;the Sayan Mountains' s and Hangay Uul's vegetation SOS was the latest in the growing season after mid-May.EOS concentrated between September 16 and October 10;Sayan Mountains' s and Hangay Uul's vegetation EOS were the earliest areas into the growing season before September.The Mongolian Altai Mountains,Hangay Uul and Sayan Mountains LOS in the northwestern Mongolian Plateau are below 110 days;the area between the Mongolian Altai and Hangay Uul in the northwestern Mongolia,most of the northern part,and the inland grassland area in the eastern Da Hinggan Mountains,LOS between 110 and 140 days.The LOS in the central,southwestern and eastern Da Hinggan Mountains areas is 160-209 days;the LOS in the southern Hetao Plain is 98-124 days;the LOS in the southeastern Ulanchab Plateau is between 140-160 days.(3)The delay of SCED and the increase of SCF and SCD in the snow season will delay the SOS and advance the EOS and shortening of the LOS for meadow steppe,typical grassland,desert steppe and alpine grassland on the Mongolian Plateau.The delay of SCOD will delay the meadow grassland SOS and advance the desert grassland EOS,making the other three grassland vegetation types SOS advanced and EOS delayed.The SCOD postponement will also delay the four grassland vegetation types LOS.(4)The effects of SCED,SCD and SCF on SOS of four grassland types in Mongolian Plateau are different in the snow season,but SCOD has the least impact on SOS of four grassland types.SCF had the greatest impact on meadow grassland SOS,followed by SCED;SCED had the greatest impact on typical grassland SOS,followed by SCD;SCD had the greatest impact on desert grassland SOS,followed by SCF;SCED had the greatest impact on alpine grassland,followed by SCF.The effects of SCOD,SCED,SCF and SCD on EOS and LOS of each grassland type in Mongolia Plateau are the same,but the degree of snow cover parameters of different planting types have different effects on EOS and LOS.SCOD had the greatest impact on EOS and LOS of four grassland types in Mongolian Plateau,followed by SCED.By analyzing the spatial and temporal distribution of snow and phenology and the impact of snow on grassland vegetation,this paper not only has important significance for global energy cycle and global climate change,but also provides information services for many fields such as ecology,agriculture and disaster prevention and mitigation.