Research On Runoff Simulation Of Small Watershed In Cold Regions Based On SWAT Mode

Runoff simulation is an important part of hydrology,and it is of great significance to find out the law of hydrological cycle in the basin.It is difficult to simulate the runoff in the cold area of north of our country because of the factors such as snowfall,snowmelt and freezing,and the small watershed is the important part of the runoff generation and confluence in the Big River basin,it is helpful to understand the whole runoff dynamic change and hydrological cycle process.Therefore,the study of runoff process and hydrological law is beneficial to the rational use of water resources,watershed comprehensive planning and agricultural irrigation.In order to study the runoff process of small watershed in cold region,this paper takes Yongcuihe River basin as the research area,selects 22 years hydrological data from1994 to 2015,and constructs the SWAT model for runoff simulation in cold region,on this basis,the applicability of different resolution DEM and different meteorological data in Yongcuihe River basin is analyzed,and the composition of runoff in the basin is analyzed,it lays a foundation for further study and improvement of runoff simulation in Yongcuihe River basin,and has some reference value for runoff simulation in small watershed in cold region.The results were as follows:(1)The SWAT model constructed in Yongcui River basin has met the requirements of model applicability in R~2,NSE and PBIAS during the period of periodic and validation,the change trend of monthly runoff simulation value is basically consistent with that of measured runoff,the simulation precision is good,and the simulation result can meet the requirement of water balance,it shows that SWAT model can simulate the runoff process of small watershed in cold region,but the simulation effect of runoff in flood season is not good.(2)The resolution of DEM has a great effect on the extraction of watershed features,but has no obvious effect on runoff simulation.With the decrease of DEM resolution,the area and the average slope of the watershed decrease,but the influence on elevation extraction is not obvious and the elevation changes little.The result determination coefficient and Nash-sutcliffe efficiency coefficient of different resolution DEM data are similar,and both of them are excellent.The runoff simulation results obtained by SWAT model driven by three kinds of meteorological data,which are measured meteorological data,CMADS data set and CFSR data set,are quite different,both the measured meteorological data and the CMADS data set can be used in the runoff simulation of Yongcui River basin,and the simulation result using the measured meteorological data is the best,and the simulation result using the CMADS data set also reaches a good level,the simulation results using CFSR data set are not good and the applicability is poor.(3)From 1994 to 2015,the annual variation range of water yield was large,and the average annual water yield was 340.46 mm,showing an increasing trend as a whole.The peak of annual water yield occurred in August,and the lowest water yield occurred in February,on the whole,it is a unimodal pattern that rises first and then falls.Among all types of land use,the deciduous forest had the largest water yield,and its annual average water yield reached 68.19%.The evergreen forest had the strongest water yield,and its annual average water yield depth was 346.39 mm.In general,the water yield of three runoff components in Yongcuihe River basin shows a rising trend in different degrees,among which the proportion of soil-middle flow is the largest,and the water yield is the largest in most years,and the increasing trend is the most significant The second is the surface runoff,which has a significant increasing trend,while the underground runoff has a slight increasing trend.(4)From 1994 to 2015,the proportion of forest area in the basin was more than 95%,and the proportion of deciduous forest area was the largest.Based on different land use,the difference of simulated water yield is less than 2mm,so the effect of land use change on water yield is not significant.The precipitation,potential evaporation and actual evaporation in the basin show different decreasing trends,and the correlation analysis shows that precipitation is the primary factor affecting water yield,the ratio of actual evapotranspiration to precipitation also has obvious influence on water yield.