Spatial And Temporal Variation Characteristics Of Snow In The Third Pole

Snow cover is an important part of the cryosphere.It can directly affect the exchange of matter and energy between the atmosphere and the earth's surface,and thus has an important impact on climate,frozen soil and biological activities.In addition,meltwater generated by snow is an important part of water cycle,and as an important water resource,it plays an important and positive role in human society.As a typical low-latitude and high-altitude snow distribution area,the Third Pole region is facing the rapid melting of snow,and its warming rate is significantly higher than the global average warming level,the warming rate is more than twice of the global average in recent decades.These phenomena have attracted extensive attention from the academic community.Therefore,based on snow cover year(all studies in this study are based on snow cover year,and the definition of snow cover year is given in section 2.3.1.1 of this paper),this study takes the Third Pole region as the main body,and makes a detailed study of snow cover and its changes in the Third Pole region from the perspective of multiple parameters based on multi-source data.At the same time,in order to comprehensively reflect the abundance level of snow cover in the Third Pole,the study compares the total snow cover water storage with the Pan-Third Pole and Arctic,which overlaps with the Belt and Road Initiative and The Silk Road Economic Belt of China,and the Arctic,which is a typical snow cover distribution area in high latitude and low altitude in terms of the total snow water storage.Firstly,the annual and monthly variation characteristics of snow cover area in the Third Pole region were analyzed by using MODIS daily cloud-free binary snow product.The spatial distribution and interannual variation of the snow cover ratio in the Third polar region are studied in detail.The phenological characteristics of snow cover(including the snow cover start,snow cover melt and snow cover duration)in the Third pole region were analyzed by using the criteria of continuous one-day snow cover and continuous three-day snow cover respectively,and the differences of snow cover phenological parameters under different evaluation conditions were analyzed in detail.In addition,the spatial distribution characteristics of average snow cover frequency in the Third pole region are analyzed.Finally,the spatial distribution of average snow cover times and the causes of snow cover distribution in the Third pole are discussed.Secondly,in order to explore the abundance of snow in the Third Pole region,this study uses five snow water equivalent products(Globsnow V2.1,Globsnow V3.0,GLDAS V2.0,GLDAS V2.2 and Can SISE)to study the total snow water storage in the Third pole region.At the same time,in order to reflect the abundance level of the total snow water storage in the Third Pole region,the Pan-Third Pole and the Arctic are included in the comparison.Firstly,this study evaluated the accuracy of five snow water equivalent products in each research area by using the snow water equivalent data measured by ground snow stations with strict quality control.Secondly,five kinds of snow water equivalent products are used to estimate the total snow water storage in the Third pole,Pan-Third pole and Arctic regions in each snow year,and analyze the interannual variation characteristics of the total snow water storage in the three regions.At last,multi-year average total snow water storage,total snow water storage interannual variation rate,multi-year average accumulated snow water equivalent,the accumulated snow water equivalent annual variation rate,The change rate of total snow water storage relative to the multi-year average total snow water storage were used to evaluate the differences between the Third Pole,the Pan-Third Pole region and the Arctic.And the relationship between climatic factors and the total snow water storage was analyzed.The conclusions are as follows:(1)From 2000 to 2015(snow year),the multi-year average snow cover area in the Third Pole was about(2.50±0.05)×106 km2,accounting for(98.44±1.85)%of the total area of the Third pole;From the perspective of the change of monthly average snow cover area,the snow cover area in the Third Pole region is in a state of continuous growth from August to January.Meanwhile,the average snow cover area in August is the smallest,and the average snow cover area in February is the largest.the region with low snow cover ratio is dominant,and the area with snow cover ratio<20%accounted for 65.86%of the whole area.At the same time,the snow cover ratio is spatially heterogeneous,and it is higher in the southwest of Pamir Plateau and Nyenqing-Tanggula Mountain,while it is lower in the Qaidam Basin,most of the southern part of the Third Pole region and the southeastern part of Qilian Mountain.The snow cover ratio in the Third polar region showed a decreasing trend.(2)The first time of snow cover in the Third pole was quite early,and the last time of snow cover was quite late.Compared with the standard of continuous one-day snow cover,the snow cover start will be significantly delayed,the snow cover melt will be significantly advanced,and the snow cover duration will be significantly shortened under the standard of continuous three-day snow cover.(3)In the Third pole and Pan-Third Pole,GLDAS V2.0,GLDAS V2.2 and Can SISE showed no strong correlation with the snow water equivalence value measured on the ground.GLDAS V2.0 and GLDAS V2.2 seriously underestimated the snow water equivalent in the Third Pole and Pan-Third Pole regions,while Can SISE had the highest accuracy in these two regions.In the Arctic region,GLDAS V2.0 and GLDAS V2.2 seriously underestimated the snow water equivalent in the Arctic region.Can SISE snow water equivalent product performed best,followed by Globsnow V3.0product and Globsnow V2.1 product.(4)During 1981-2010(snow year),the multi-year average total snow water storage in the Third Pole,Pan-Third Pole and Arctic regions was 46.07±7.44 km~3,277.21±37.30 km~3 and 1249.17±81.42 km~3,respectively,the multi-year average accumulative snow water equivalent is 18.14 mm,22.93 mm and 93.15 mm,respectively.The average annual accumulated snow water equivalent in the Arctic region is much higher than that in the Third and Pan-Third polar regions,and the Third polar region is the smallest.The decrease rate of accumulated snow water equivalent in the Arctic region is significantly higher than that in the Third polar region and the Third Polar region,and the Third polar region is the lowest.Meanwhile,the decrease ratio of total snow water storage in the Third Polar region relative to the annual average snow water storage is the fastest,which is significantly higher than that in the Pan-Third Polar region and the Arctic Region.The variation of total snow water storage is probably closely related to temperature and snowfall.The total snow water storage will decrease with the increase of temperature or decrease of precipitation,and increase with the decrease of precipitation.