Evaluation On The Contribution Of Snowmelt To Spring Runoff In The Baishan Basin Of The Cold Northeast Region

Snow is important storage of water resources on earth.The snowmelt effect of snow makes snowmelt water a significant supply source for rivers and lakes,and in some mid-latitude arid and semi-arid mountainous areas,snowmelt water is a vital source of spring runoff,which has an impact on the regional surface water cycle,the distribution of water resources and human production and life,so snow is an important freshwater resource in China and a strategic resource.Northeast China is one of the three stable snow areas in China.As an important production base for agriculture,forestry and animal husbandry,its snow is not only an important supply of rivers and groundwater in the region but also plays a good role in water storage and heat preservation of soil,which can provide suitable temperature and conditions for crops in the overwintering process.Therefore,studying the characteristics of seasonal snow cover and the runoff generation and confluence mechanism of snowmelt runoff,accurately quantifying snow reserves,and evaluating the contribution rate of snowmelt to spring runoff is of great help to grasp the characteristics of spring water resources in the basin and the reasonable storage of reservoirs in the basin while improving the utilization rate of snowmelt water and ensuring the efficient development and utilization of water resources.Accurate modeling of spring runoff processes is the basis for evaluating the contribution of snowmelt to spring runoff.Snow accumulation,snowmelt and sink production have significant spatial variability and are closely related to regional physical geography and hydro-climatic characteristics.How to reasonably grasp the snow accumulation characteristics of the watershed to determine the snow accumulation and snowmelt parameters of the SWAT distributed hydrological model,to improve the accuracy of spring runoff simulation is the key research content of this paper.In this paper,the spatial and temporal evolution patterns of snow accumulation in the basin are analyzed by statistical and trend analysis methods to understand the snow storage,distribution characteristics and duration in the basin,and to evaluate the snow resources in the study area,taking the Baishan reservoir basin in the second Songhua River source section as an example.A distributed hydrological model is constructed to simulate the spring snowmelt runoff process,and the snowmelt parameters of the model are optimized according to the snowpack characteristics of the basin to improve the accuracy of the spring snowmelt runoff simulation,and to assess the contribution of snowmelt to the spring snowmelt runoff,as well as to analyze the changes in spring snowmelt runoff under climate scenarios.The following main results have been achieved:(1)Analysis of the spatial and temporal evolution of the snowpack in the basinBased on MODIS10 A snow cover rate data,snow depth data retrieved by snow remote sensing and snow days data,the temporal and spatial evolution trends of snow cover rate,snow depth and snow days in the watershed were analyzed by mathematical statistics.From 2000 to 2018,the annual snow cover rate and snow days did not change significantly,and the annual snow depth showed an indigenous increasing trend,with a change rate of 2.12 cm / 10 years.In terms of spatial distribution,the annual snow days are generally characterized by more high-altitude mountainous areas,less low-altitude plain areas,more high-latitude areas and less low-latitude areas.Among them,Changbai Mountain is the most,reaching 147 days/years.The multi-year accumulated snow depth and snow cover rate show three high-value areas in space,namely the Changbai Mountain area,the high-altitude area in the western Baishan City of the study area and the mountainous area in the eastern Yanbian Korean Autonomous Prefecture.(2)Simulation of spring runoff processes in the basinThe SWAT distributed hydrological model of Baishan Basin was constructed,and the model parameters were calibrated based on the daily runoff data of Baishan Reservoir.On this basis,according to the characteristics of snow cover in the basin,the probability intersection method,the critical temperature method and the degree-day factor method were used to calculate the critical temperature of rainfall-snowfall(SFTMP),the snow melting temperature threshold(SMTMP)and the maximum and minimum degree-day factors(SMFMX,SMFMN).The snow cover and snow melting parameters of the model were determined,and the snow melting runoff process in spring was simulated.The simulation accuracy was 21 % higher than that of the original,and the annual runoff simulation accuracy was also improved by 10 %.(3)Evaluation on the contribution of snowmelt to spring runoffThe contribution rate of snowmelt to spring runoff in the basin was counted.The spring runoff depth accounted for 29%～47% of the annual runoff depth,and the snowmelt accounted for 14%～33%of the annual runoff depth.From the perspective of annual runoff depth,the basin was mainly dominated by summer rainfall runoff.Snowmelt accounts for 59%～79% of spring runoff depth.From the perspective of spring runoff depth,snowmelt runoff is the main runoff in spring.The contribution rate of snowmelt in different land-use types to spring runoff depth was counted.The snowmelt in cultivated land accounted for 36% of spring runoff depth,28% in forest land,35% in grassland,and the proportion of forest land was the smallest.There was little difference between cultivated land and grassland.(4)Analysis of the evolution of spring runoff driven by climateBased on the SWAT model,a single climate factor scenario with 5% and 10% increase in precipitation and 1.5°C and 3°C increase in temperature and CMIP6 future climate model data are used to simulate spring snowmelt runoff.The influence of single climate factor change on runoff and the evolution trend of runoff in the future climate model are analyzed.The precipitation increased by 5% and 10%,and the snowmelt runoff increased in March and April.When the precipitation increased by 5%,the snowmelt runoff in spring increased by 9% more than that of precipitation by 10%.When the temperature increased by 1.5°C and 3°C,the snowmelt runoff increased in March,while the snowmelt runoff decreased in April.Moreover,when the temperature increased by 3°C,the snowmelt runoff in spring increased by 6.9% compared with that when the temperature increased by 1.5°C.Therefore,driven by a single climatic factor,the precipitation factor is the dominant factor of runoff change,followed by the temperature factor.The temperature factor is less sensitive to runoff than the precipitation factor.Driven by the comprehensive climate of precipitation and temperature,the average spring snowmelt runoff in March and April decreased by60.6% and 22.3% compared with the spring snowmelt runoff in March and April(the average of2010～2019).The research results of this paper provide the basis for water resources management and allocation in spring snowmelt runoff prediction,agricultural sowing and reservoir storage in cold regions of Northeast China.