Simulation Study On Snow Melt Change And Its Impact On Runoff In Cold Region

Seasonal snow cover is common in alpine regions in China,which makes the climate and runoff change process in these regions have unique characteristics compared with other regions.On the one hand,the snow cover on the surface in winter has the function of preserving soil moisture and heat preservation.The snowmelt runoff generated by snow melting in spring is an important freshwater resource and an important part of runoff,which can provide rich water resources for agriculture,forestry irrigation,residential water and industrial water.On the other hand,the process of snow and snowmelt is extremely sensitive to climate change and underlying surface conditions.The temperature affects the amount of snow in winter and the accumulation of snow.The rapid rise of temperature in spring makes a large amount of snow melt in a short time,which may lead to spring flood.At the same time,the occurrence time of snowmelt runoff plays an important role in the rational application of snowmelt water resources.The refore,Exploring the influencing factors of snow melting and the simulation and prediction of snow melting runoff is of great significance for drought prevention and rational utilization of water resources in seasonal snow area in spring.Northeast China is one of the three snow covered areas.Taking the Hulan River Basin on the left bank of Songhua River as an example,based on the collected measured runoff data of the study area from 1982 to 2000,the relative humidity,wind speed and sunshine hours of f our meteorological stations from 1982 to 2000,the highest and lowest temperature from 1960 to 2000,the rainfall data of 43 rainfall stations from 1982 to 2000,the soil data map,digital elevation map（DEM）and land use map of the study area in different years.Firstly,compare the land use conversion types and soil database in the study area,preliminarily analyze the temperature change in the year,determine the snowmelt runoff time and divide the snowmelt runoff period,simulate the snowmelt runoff process through SWAT（soil and water access tool）model,determine the key factors affecting snowmelt runoff,and explore the change characteristics of snowmelt runoff in seasonal snow area and its sensitivity to climate.The main conclusions are as follows:（1）The snowmelt runoff is identified according to the basic flow segmentation theory and digital filtering method.The daily runoff of Hulan River Basin in 19A is divided into snowmelt runoff,and the start time and end time of annual snowmelt runoff are determined by analyzing the change trend of snowmelt runoff ratio and runoff process curve.According to the multi-year average change trend,the snowmelt runoff time is from April 2 to April 27,with an average duration of 25 days.Based on the analysis of the multi-year variation trend of monthly average flow and monthly fractional flow（mfs）of snowmelt runoff,the average flow and mfs in March show an upward trend,with growth rates of 1.796m3·S^-1/10 and 0.166/10 years respectively;The average flow in April has a downward trend,while the MFS has a positive growth,and the change rates are 15.5m3·S^-1/10 years and 0.376/10 years respectively;The average flow and MFS in May showed a downward trend,with the reduction rates of 58.829m3·S^-1/10 and 2.703/10 years respectively.（2）SWAT model snowmelt runoff simulation.The land use and soil types are reclassified,and the meteorological and soil attribute database is constructed as the model input.The research period division rate is regularly compared with the verification period,the model parameters are calibrated and the more sensitive parameters are determined,and the accuracy of the model is evaluated by the certainty coefficient D_C,which reaches 0.81 and 0.79 respectively.（3）Through the division of rainfall and snowfall and the simulation of snow amount and snow melting amount by SWAT model,the change trends of snow period temperature,start time of snow melting period,length of snow period and maximum snow amount are analyz ed.Among them,the temperature in snow period has shown an upward trend for many years,with an average growth rate of 0.85℃/10 years;The beginning time of snowmelt has shown a downward trend for many years,with a reduction rate of 1.02 days/10 years,and the change trend is not significant;The average length of snow cover period in Hulan River Basin is 130 days,which shows a decreasing trend over the years,with a decreasing rate of 15.7 days/10 years.The delay of stable snow cover period in winter has a greater impact on the length reduction;The maximum snow cover is greatly affected by land use and topographic slope,so the multi-year change trend is different in the basin.Among them,the maximum snow cover in the plain area where hailun and Mingshui meteorological stations are located in the west of the basin shows an insignificant decreasing trend,and the steep slope land where Tieli and Beilin meteorological stations are located in the East shows an increasing trend.（4）The sensitivity coefficient method is used to calculate the sensitivity of snowmelt runoff in different months to six meteorological factors:snowfall,snowmelt,snow depth,length of snow period,temperature of snow period and temperature of snow melting period.The most sensitive factor is the runoff in March to the temperature of snow period,with a sensitivity coefficient of3.28.The sensitivity of snowmelt runoff to the length of snow period is the weakest,and the snowmelt runoff in April is more sensitive to sensitive parameters.The sensitivity of runoff to snowfall,snowmelt,maximum snow cover and length of snow cover period of hailun and Tieli meteorological stations is positive,while it is negative to the characteristic parameters of Mingshui and Beilin meteorological stations.