Hydrologic Cycle Of Typical Small Watershed At Alpine And Altitude In The Source Region Of The Yangtze River

The source region of the Yangtze River is located in the Qinghai-Tibet Plateau,which has been significantly affected by climate change in the past decade.The hydrological cycle in the source region has changed,the spatial and temporal distribution pattern of water resources has changed,and the eco-system has been threatened.This series of issues has become the focus of widespread attention at home and abroad.This paper takes the Dongkemadi basin in the source region of the Yangtze River as the research area,collects data through automatic station and field work,and careful analyzes the various elements of the water cycle in the Dongkemadi basin.The CRHM is used to build the hydrological model of the cold region.The runoff process of the Dongkemadi basin is simulated and analyzed.Combined with quantitative analysis and numerical simulation,the water cycle process in the source region of the Yangtze River is summarized.The following conclusions have been obtained:(1)Analysis of the characteristics of hydrometeorological elements in the Dongkemadi basin of the Yangtze River source area.The results show that the temperature has an increasing trend.The annual average temperature is-5.06°C,and only in June-September is above 0°C,the temperature for the rest of the year is below 0°C.The corrected precipitation increased by about 13%,and the annual cumulative precipitation showed a slight increase.The precipitation was unevenly distributed during the year,mainly concentrated in June-September,accounting for 78%of the total annual precipitation.The solid precipitation lasted a long time,liquid precipitation time is mainly concentrated in June-September,but liquid precipitation is the main source of precipitation,accounting for about 60%of total precipitation.The evapotranspiration of June-September was increasing,and the rate of increase was faster.The calculated evapotranspiration was calculated by the modified Takahashi formula to be close to the actual evapotranspiration,with a relative error of 4%.(2)Analysis of the change of temperature and humidity of frozen soil can be concluded that the shallow soil began to thaw in about May,and began to freeze between October and November.The deep soil thawing time is around July,and the freezing time is about December.The soil is frozen for a long time,and the melting time is only between 100-150 days.The change of soil moisture is obvious and rapid.From May to July,the soil in each layer is shallow to deep,and the humidity increases in turn.It rises rapidly to about0.4,is in a saturated state,and falls to a minimum after freezing in October-December.(3)The law of runoff variation in the Dongkemadi basin and the correlation analysis between runoff and various meteorological elements.The runoff in the warm season(June-September)has been increasing for many years,and the trend of runoff change is dry-rich-dry,the years runoff distribution is uneven.From June to September,it accounts for 80%of the annual runoff,of which the maximum runoff in August is 101.1×10~5m~3,and the runoff in June is the smallest 38.4×10~5m~3.The driving factors of runoff process are analyzed.The runoff has a significant exponential relationship with temperature,the fitting degree is R~2=0.7.The relationship between runoff and precipitation is not obvious.The influence of temperature on runoff is more direct than the impact of precipitation on runoff.When the temperature is lower than 2-4°C,the effect of precipitation on runoff is reduced.Although precipitation occurs,the runoff remains unchanged.When the temperature rises above 4°C,precipitation is the main influencing factor of runoff.When precipitation occurs,the runoff has a flood peak.(4)According to the basic characteristics of the Dongkemadi basin in the source region of the Yangtze River,a climate hydrological response model suitable for the study area was established by CRHM.The model considers the solid-liquid separation in the form of rainfall in cold climate,the infiltration process of frozen soil,and glacial ablation to the river.The runoff process of the Dongkemadi basin in the source region of the Yangtze River is well simulated.The correlation coefficient between the simulated and observed values of daily runoff is R=0.83,and the model Nash efficiency coefficient is NSE=0.66.The correlation coefficient between the simulated value of the ten days runoff and the observed value is R=0.97,NSE=0.93.(5)Combining quantitative analysis and numerical simulation to analyze the water cycle process in the source region of the Yangtze River.The precipitation form is divided into liquid and solid under the influence of low temperature in the cold region;The melting of permafrost and the concentration of precipitation make the soil water abundant for a time,which can continuously supply evapotranspiration and flow into river runoff;glacial ablation provides stable and large recharges to river runoff.