A Study On Influence Of Snow Cover On Soil Water And Heat In The Farmland In Northeast China

It is of great significance to study the influence of snow on soil water and heat.It can provide scientific guidance for agricultural production,agricultural irrigation,water resources regulation and so on.It provides a theoretical basis for monitoring and forecasting soil moisture in spring.The heat preservation effect of snow has an important influence on the temperature and moisture change and energy balance of the soil on the underlying surface.As an important fresh water resource on land,the snow accumulated a large amount of water after melting,which can change the hydrological condition of the soil,and the soil moisture is closely related to the winter snow accumulation parameters in spring.In this paper,using physical process model and remote sensing monitoring,two methods of model simulation and remote sensing data are used to study the influence of snow on soil water and heat.Microwave remote sensing inversion of snow and soil moisture is widely used for all-weather,all day and wide range.For the temperature of frozen soil below ground surface,the remote sensing method cannot be detected and obtained due to the effect of snow cover in winter,and the physical process model based on the snow thermal model(SNTHERM)can accurately predict and simulate the change process of frozen soil temperature in the underlying surface,which is feasible for the study of the influence mechanism of snow cover on soil temperature.The main content of this paper is divided into two parts.The first part is the study of the influence of snow on the frozen soil temperature based on the physical process model.First,the sensitivity analysis and accuracy evaluation of the physical process model have been carried out.It is found that the simulation accuracy of the model for soil temperature is high,but the simulation effect on soil moisture,especially in spring soil moisture,is not good.Therefore,the influence of snow parameters on the temperature of the underlying surface frozen soil is studied by the physical process model.The second part,based on remote sensing data products,uses GIS geoscience statistics to analyze the effects of winter snow cover parameters(maximum snow depth,mean snow depth and duration of snow cover)on soil moisture in spring in the northeast of China,and establish a regression equation between snow parameters and soil moisture in spring.The main conclusions of this paper are as follows:(1)The sensitivity analysis of SNTHERM meteorological driven data shows that soil temperature and moisture are most sensitive to atmospheric temperature and long wave radiation flux,and the sensitivity analysis of initial soil characteristic parameters shows that soil temperature is not sensitive to initial input soil characteristic parameters(RMSE<1 C),and soil moisture is most sensitive to soil plastic index.Therefore,accurate acquisition of atmospheric temperature and long wave radiation flux in meteorological driving data and plasticity index of soil can improve the accuracy of model simulation.(2)Under the condition of snow cover,SNTHERM can effectively simulate and predict the temperature of seasonal frozen soil.The simulation accuracy for shallow soil layers(5cm,10 cm,15cm)is better than the deep soil layers(20cm,40 m).Under the condition of snow cover,the root mean square error of the shallow soil is within 2 ?.The results show that SNTHERM can be used to simulate the temperature of the shallow frozen soil under the snow cover,which provides a new way of the inversion of the seasonal frozen soil temperature.(3)The effect of snow cover on the temperature changes of the shallow layer of the underlying surface is significant,but the influence on the soil moisture is not obvious,mainly because the frozen soil is frozen,the liquid water is low,and the liquid water migration is very small.The change of soil temperature has a certain relation with the thickness of snow cover.When the thickness of snow is above 5cm,the change of soil temperature in the underlying surface is significant.With the increase of snow thickness,the better the effect of snow insulation.(4)The correlation analysis between the snow parameters and soil moisture of April and May in 1980-2009 year shows that the annual snow parameters have a significant positive correlation with soil moisture(confidence level <0.05)in the Northeast farmland,which is more than 45% of the study area,and the effect on soil moisture in April is better than that in May.The fitting effect of the maximum snow depth and soil moisture is better than the fitting effect of the average snow depth,the number of snow days and the soil moisture.The fitting effect of the maximum snow depth and the soil moisture in December are better than that in the other months.The results show that the maximum snow depth can be used as an important snow parameter for the prediction of soil moisture in spring.