Study On Spatial-Temporal Variation Of Snow Water Equivalent Loss In Eurasia And Its Relationship With Climate Change

Seasonal snow cover is a key part of surface energy and the water cycle,as well as an important freshwater resource.Eurasia is the main distribution region of snow cover across the Northern Hemisphere.This study corrected precipitation data and systematically calculated the characteristics of snowfall and snow cover,and the loss of snow cover during its accumulation period in Eurasia from 1966 to 2016 by using ground observations,including precipitation,air temperature,snow depth,snow water equivalent?SWE?,wind speed and relative air humidity.Then we analyzed the regional distribution and temporal variations of snow mass loss and explored the relationship between SWE loss and climate change.The main conclusions are summarized as follows:?1?The spatial distribution of snowfall during the snow accumulation period?SAP?in Eurasia has significant regional differences.The multi-year mean snowfall in Sakhalin,the Kamchatka Peninsula,and northern Siberia is heavy and can be 400 mm.Three major snow cover regions in China?Xinjiang,Northeast China,and the Qinghai-Tibet Plateau?generally have lower snowfall.The amount of snowfall in most of China is less than 100 mm except for the Qinghai-Tibet Plateau,which multi-year mean snowfall can reach more than 100 mm.Taking 1971—2000 as the climatic base period,snowfall anomaly across the study area from 1966 to 2016 decreased at a rate of 2.8mm/10yr.For each site,snowfall is decreasing in the Eastern European Plain,most parts of Siberia,and the Qinghai-Tibet Plateau.However,snowfall is increasing in northern West Siberia,the Lena River Basin,Sakhalin,Xinjiang,and Northeast China.?2?As the latitude increases northward across the study area,the days of SAP gradually increase.For every 1°of increase in latitude,the SAP is prolonged by nearly4 days.The SAP in Northern Siberia?north of 65°N?lasts for longer time and the days of SAP are more than 200 days.The SAP in the Eastern European Plain is between 50and 200 days and it is between 50 and 150 days in China.The anomaly of days of SAP across the study area from 1966 to 2016 decreased at a rate of 2.3 days/10yr.For the maximum SWE,in the Kamchatka Peninsula,it is the highest,which can be above 350mm in some areas.Generally,maximum SWE is between 50 and 200 mm in the Eastern European Plain and Western Siberia.It is within 100 mm across three major snow cover regions in China.Relative to 1971—2000,the maximum SWE anomaly across the study area increased at a rate of 1.4 mm/10yr from 1966 to 2016.And Sakhalin is the region where the trend of maximum SWE increases more significantly.But in the Lena River Basin,northern part of Eastern Siberia and Eastern European Plain,the maximum SWE decreases.?3?The amount of snow loss?SLA,the difference between snowfall and maximum SWE?and snow loss ratio?SLR,the ratio of SLA to snowfall?are two parameters which are used to measure SWE mass loss during SAP in Eurasia.The spatial distribution characteristics of SLA and SLR are not consistent.Although there is a good consistency between SLA and SLR in some areas?both are relatively large,such as in Northern Siberia;both are relatively small,such as in the Lena River Basin?,in some regions the SLA is at a low level and the corresponding SLR is high?such as in the Eastern European Plain?.The anomaly of SLA and SLR are both decreasing from 1966 to 2016relative to 1971—2000 and the reduction rates are 4.9 mm/10yr and 2.1%/10yr,separately.For most sites,the trends of SLA and SLR are accordant and both of them are decreasing.?4?Climate change contributes to the changes of SLA and SLR.The average temperature and relative air humidity anomalies during SAP from 1966 to 2016increased at the rate of 0.2?/10yr and 0.2%/10yr,respectively,but the mean wind speed anomaly decreased at a rate of 0.2 m·s^-1/10yr.Compared with air temperature and relative air humidity,the SLA and SLR have the strongest correlation with wind speed.For every 1 m/s of increase in wind speed,the SLA increases by 27.25 mm and SLR raises by 5.79%.The SLA and SLR of most sites keep a positive correlation with air temperature and wind speed.For the relative air humidity,the SLA and SLR in China are both negatively correlated with it.In northern Mongolian Plateau,the SLA is positively correlated with relative air humidity,but SLR keeps negatively correlated with it.Therefore,the change of snow mass loss is caused by the decreasing of wind speed and the increasing of temperature.The decrease in wind speed leads to a reduction in SLA.At the same time,the increasing air temperature results in a decrease in snowfall.Because the rate of snowfall reduction is slower than the decrease rate of SLA,so the SLR is also decreasing.Also,the decrease of snow mass loss in SAP is associated with the increase of maximum SWE,then it provides more snow melting water in spring under climate warming.Under the background of global warming,snow mass loss directly affects the redistribution of snow cover,total snow reserves,and snowmelt in the coming spring,which in turn influences snow water resource assessment and its rational utilization.However,at present,there are few studies on the snow mass balance during accumulation period,and most of them are based on model simulation.With the help of ground observations,this study explored the mass changes of Eurasian snow cover during its accumulation period,and analyzed their relationship with climate change.This is closely related to social production and human life,and has important practical significance.