| The response of cryosphere to atmosphere and hydrosphere is direct and sensitive.The cryosphere is the embodiment of the solid form of the hydrosphere.With its huge ice reserves and heat capacity,it regulates the water energy balance on the earth and is the second largest climate system.Snow is the most active element in the cryosphere,covering the widest area and also an important part of the cryosphere.It contributes a lot to hydrological cycle.Snow is an important freshwater resource for human beings,which affects the global climate and atmospheric circulation.The study of temporal and spatial variation of snow depth and snow cover in Xinjiang is helpful to understand the climate and environment change in this region.The analysis of the temporal and spatial variation of the number of snow melt floods and snowstorms is of certain guiding significance for the disaster prevention and mitigation in this area.Based on the collected snow depth data(1961-2015),snow pressure data of some stations(1980-2013)and meteorological data,EOF is used to analyze the original snow depth data to obtain the temporal and spatial distribution of snow depth.The trend and change of snow depth are obtained by MMK test,and the periodic distribution of snow depth and snow pressure are obtained by complex Morlet wavelet analysis.Using Daubechies wavelet to get the overall trend of annual snow depth and snow pressure.Finally,using cross wavelet to get the correlation between annual snow depth and meteorological factors.Based on the MODIS Snow Cover product data MOD10A2 in 2001-2018,the snow cover data of Xinjiang in2001-2018 is extracted.Thus,the temporal and spatial variation of snow cover area percentage and the temporal and spatial variation of snow cover area percentage under different slope directions and different elevation zones are analyzed.Based on the records of the occurrence of snow melt floods in Xinjiang(2000-2012),the temporal and spatial distribution characteristics of the occurrence of snowmelt floods in Xinjiang in the past 13years are revealed,as well as the correlation between the number of floods and the accumulated precipitation in the winter half year.Based on the records of snow disasters in Xinjiang from 1960 to 2000,the temporal and spatial distribution characteristics of snow disasters in Xinjiang are revealed.The main conclusions are as follows:(1)The EC1 curve of snow depth decomposed by EOF showed an upward trend in four months(December,January,February and March),except October and November.The monthly and annual EC1 curves are in good agreement with the measured snow depth.The monthly and annual EOF1 of Northern Xinjiang is higher than that of Southern Xinjiang.The abrupt change point of annual snow depth mainly occurred in 1969-1979 and 1980-1990.The stations with main periods of 2-8 years and 9-14 years(15-20 years)are mainly distributed in the North(southwest)of Xinjiang.The annual snow depth(annual snow pressure)is increasing in Xinjiang.There is a good correlation between the annual snow depth(monthly,annual snow pressure)and precipitation(relative humidity),and a weak correlation between them and the minimum temperature(or sunshine hours).In October and November,the snow pressure showed no obvious downward trend,but in December,January,February and March,the snow pressure trend was not obvious,and the overall trend of annual snow pressure change showed an upward trend.The snow pressure in October,November and December has obvious main period,but there is no main period in January,February and March.(2)The annual mean snow cover area is 468700 km~2,the maximum snow cover area is1346100 km~2,and the minimum snow cover area is 124400 km~2.In autumn and summer,the snow cover area percentage shows a weak decline trend,and the seasons showing a significant decline trend are spring and winter,respectively.The seasonal dynamics of snow cover can be divided into three stages:the snow cover period from September to January,the snow cover area continues to expand from high-altitude mountains to valleys and plains;the snow cover area gradually reduces from Plains to mountains in the snow melting period from February to June;the annual snow cover stage(July to August),in which the annual snow cover is almost completely distributed on the high mountains in the study area.The snow cover area percentage of Southwest slope,Southeast Slope and south slope is lower than other five slope directions.<1000m?1000-2000m?2000-3000m?3000-4000m.The snow cover area percentage of the four altitudes of<1000m,1000-2000m,2000-3000m and3000-4000m is the highest in winter,the lowest in spring,and the lowest in summer,and the increase in autumn,which shows a"concave"change process as a whole.the snow cover area percentage of the altitudes of 4000-5000m has three change stages:stable fluctuation period,decrease period and increase period.There are two periods of rise and fall of snow cover area percentage in 5000-6000m altitude zone.the snow cover area percentage in>6000m altitude zone shows a"convex"change process as a whole,with the maximum value in summer and the minimum value in spring.(3)According to the overall spatial distribution characteristics of flood frequency,Changji,Yili and Hetian regions are the high-risk areas of snowmelt flood in Xinjiang,and Fengxian,Xinyuan and Qinghe counties are the high-risk areas of snowmelt flood.In terms of the seasonal spatial distribution characteristics of flood frequency,in spring,Northern Xinjiang is a heavy disaster area of snowmelt flood,especially from Eastern Altay,northern Tacheng,Ili River Valley,Changji area to Urumqi.in summer,Hetan Area in southern Xinjiang and southern Kezhou are both high incidence areas.In terms of the distribution of flood times,the snow melt flood occurred the most frequently in 2010(34 times),which was closely related to the accumulated precipitation in the winter half year.According to the seasonal distribution of flood frequency,snowmelt flood mainly occurs in spring and summer in Xinjiang.According to the spatial distribution characteristics of snow disaster frequency,according to the county distribution,Tacheng,Kashi and Hami are the high incidence areas of snow disaster.From the age distribution characteristics of snow disaster frequency,it can be seen that the most frequent occurrence of snow disaster was in 1987,24 times,accounting for9.10%of the total number,followed by 1978,16 times,accounting for 6.10%of the total number.There was no snow disaster in 1962 and 1973.According to the seasonal distribution characteristics of snow disaster frequency,Xinjiang snow disaster mainly occurs in spring and summer. |
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