The Study On Snow Hydrological Process Of Larix Gmelinii Forest In Daxing'an Mountains

Seasonal snow cover is an important part of the climate system in high-latitude regions.The Daxing'an Mountains is also one of the important water conservation functional areas in my country.The typical local climate is characterized by long and cold winters and a long period of time for surface snow cover.The hydrological process and the law of hydrological change are very important in regional hydrological research.Larix gmelini is a zonal vegetation in the Daxing'an Mountains.With the global warming,the trend of climate abnormalities intensifies,and the phenomenon of global abnormal climate becomes more and more intense,leading to the shortening of the snow accumulation period and the advancement of the snow melting period and other abnormal climate phenomena.How to understand the snow hydrological change process of the Larix gmelini forest in the north of the Daxing'an Mountains is of great significance for evaluating the characteristics of local snow water resources and planning and utilization.At the same time,the influence of environmental factors on the snow hydrological process of Larix gmelini forest in the cold temperate zone is also a scientific issue that needs to be revealed urgently.Therefore,this study takes the natural forest of Larix olgensis in the cold temperate zone of the Northern Daxing'an Mountains as the research object.Through the study of the characteristics of snow hydrological changes for three consecutive years.the relationship between the Larix gmelini forest and snowfall,snow cover and snowmelt is studied,and at the same time quantified.The relative contribution of environmental factors to the change of snow hydrological process is evaluated,aiming to reveal the change characteristics of forest snow hydrological process in this region,with a view to the sustainable management of regional forests and water resources in the context of global climate change.Provide theoretical basis,the research content is as follows:(1)During the entire observation period,the deepest snow depth in the forest plot was 68.6cm,and the deepest snow depth in the plot outside the forest was 74.8cm.It shows that Larix gmelini forest has a certain ability to intercept snowfall,but its ability to intercept snow only has a significant effect in light snow.When simulating with the Andreadis snowfall interception model,the simulated value is too high.After the non-linear regression iterative analysis through the spss software,it is concluded that the improved Andreadis model has a good correlation with the measured value.(2)During the snow-packing period,the change in snow density and snow water equivalent in the Larix gmelini forest plot was not significantly different from that in the open space plot(P>0.05).At the same time,when wind and snow occurred in the plot,the wind blowing snow would affect the deciduous leaves.The impact of snow water equivalent in the pine forest is relatively small.To a certain extent,the forest cover has increased the ability to control snow hydrological processes.reduced snow evaporation loss.and has a positive effect on the forest water conservation function to a certain extent.(3)During the snow-packing period,net radiation and wind speed are the main factors affecting the snow evaporation rate.The average snow evaporation of the control plot outside the forest increased by 7%compared to the forest plot,and the average snow evaporation rate increased by 9.2%;During the snowmelt period,temperature and net radiation are the main factors affecting the snow evaporation rate.Fresh snow layer also has an impact on the intensity of snow evaporation rate during the snowmelt period.After a snowfall event occurs during the snowmelt period,the amount of fresh snow snow evaporation is 3.58 times that of Deep snow layer,and the snow evaporation rate of fresh snow is 6 times that of Deep snow layer;indicating that during the snowmelt period,snowfall and the gradual increase in temperature affects the intensity of snow evaporation during this period.Meteorological factors are the main reason for the difference in the increase in snow evaporation.(4)When the Penman joint method is fitted with vorticity data,the fitting value is relatively high.Its R2 values are 0.578.0.562 and 0.532 in different snowmelt periods,respectively,and the fitting degree is good.The Penman joint method is used to improve the vorticity data.The RMSE of the improved Penman joint method from 2016 to 2018 were 0.052.0.057,0.059;R2 values were 0.781,0.749,and 0.751,respectively.The results obtained the snow evaporation measured by the improved Penman joint method and the vorticity correlation method The rate fit is better.The improved Penman combination method can be used to determine the snow evaporation rate during the snowmelt period in other forest types that are not covered by flux towers,and can ensure the continuity and accuracy of the snow evaporation data in different local areas.(5)During the snowmelt period,with the formation of snowmelt runoff,the snowmelt water of the Larix gmelinii forest maintains a certain permeability in the 5 and 10 cm soil layers.When a snowfall event occurred during this period,the total snow water equivalent in the Larix gmelini forest increased,but the snowmelt water infiltration volume hardly increased.Through time series correlation analysis and mutation point analysis,it is found that the snowmelt water infiltration below 20cm soil layer has been in a state of no snowmelt water infiltration compared to the soil layer above 10cm.(6)Soil energy change is one of the key factors affecting the infiltration of snowmelt water.During the research period,the change period of soil energy was accompanied by the increase of soil depth,and its change period increased to a certain extent.During the entire snowmelt period,the complexity order of soil temperature sequence at different depths in the Larix gmelini forest plot was:5cm soil temperature>10cm soil temperature>20cm soil temperature>40cm soil temperature.It shows that with the increase of soil depth,the change trend of soil energy budget weakens,and at the same time,the surface layer of snowmelt water cannot thaw the frozen soil of this layer,which hinders the infiltration of snowmelt water.(7)During the snowmelt period,the Larix gmelini forest in the northern part of the Daxing'an Mountains presents a unique inverted U-shaped curve from the formation of runoff to the decline of runoff discharge,and has the characteristics of typical mountain snowmelt runoff.Environmental factors such as snow cover and temperature have the greatest impact on the rate of snowmelt runoff,and 2016,with the largest snow cover,has the strongest impact on snowmelt runoff.Compared with the wilderness plot,the snowmelt runoff in the Larix gmelinii forest plot has a slower growth rate,less snowmelt runoff,and the overall fluctuation range is relatively stable,indicating that the Larix gmelinii forest has the functions of reducing the rate of snow and aquatic runoff,reducing soil erosion,and has the function of reducing water and soil erosion.A certain holding effect.(8)There was a significant difference in anions in the snowfall between the sample plots inside the forest and the open space outside the forest(P<0.05),but the difference in cations was not significant(P>0.05).With the passage of time,the anions in the snow in the forest plots and the open spaces outside the forest gradually accumulate in the Deep snow layer.The content of anions in the Deep snow layer in the forest plots is relatively high,but compared with the Deep snow layer in the control plot outside the forest.In comparison,the difference is not significant,and the difference is not significant in both the fresh snow layer and the medium snow layer(P>0.05).The physical and chemical changes of snow in the forest plot of Larix gmelini are consistent with the dynamics of the open space outside the forest,indicating that the forest canopy closure is lower in the Larix gmelini forest due to deciduous leaves in winter,and the nutrient accumulation capacity in the snow is different from that of the wilderness plot.