Study On The Evolution Law And Future Trend Of Runoff In The Three-River Headwaters Region

The Three-River Headwaters Region is a sensitive area in response to climate change.Under the influence of human activities and climate change,the changes in its water resources are extremely important to the water security of my country's Yellow River,Yangtze River,Lancang River and even eastern Asia.Therefore,understanding the evolution of runoff in the Three-River Source Region,clarifying the driving factors of runoff changes,and analyzing the impact of climate change provide scientific guidance and basis for water resources protection and ecological environment protection in the Three-River Source Region and water resources planning and management in my country's main river basins.This paper uses the source of three rivers as the research area,using ESMD time series analysis methods and spatial analysis methods to identify hydrometeorological elements and land use change characteristics in the source area of the three rivers;construct a SWAT model for the three rivers source area,and finely simulate the precipitation and runoff in the source area Spatial and temporal distribution characteristics;quantitative separation of the effects of land use change,precipitation and temperature on runoff changes;coupled with the statistical downscaling results of global climate models to predict the future change trend of runoff under different climate scenarios in the Three-River Source area,the main research results of this paper as follows:(1)Precipitation in the Three-River Headwaters Region all showed an increasing trend;the maximum temperature/minimum temperature changed slightly;except for the decrease in the runoff at the source of the Yellow River,the runoff at the source of the Yangtze River and the source of the Lancang River showed an upward trend,and the trend changes were particularly significant after the 1990 s.Both precipitation and temperature had abrupt changes around 1990;through a variety of comparisons,it was found that the most likely year of abrupt change in runoff was 1990;the analysis of the7 th phase of the Three Rivers Source land use type transfer and change,the land use change took 1990 as the node After 1990,the change and transfer of land use accelerated.(2)The SWAT model has better applicability in the Three-River Headwaters Region.The simulation of the spatial distribution of precipitation and runoff in the source area found that the spatial distribution characteristics of precipitation and runoff were not completely consistent.The precipitation gradually increased from northwest to southeast,while the spatial distribution of runoff had no obvious law to follow;quantitative separation of land use around 1990 Changes,precipitation and temperature changes affect runoff.Compared to before 1990,precipitation changes after 1990 are the direct cause of runoff changes,and their contribution rate exceeds 70%.(3)Use the ASD model to input the precipitation and temperature statistical downscaling results of the global climate model(INM-CM4-8)under three scenarios(SSP1-2.6,SSP2-4.5,SSP5-8.5)into the calibrated SWAT model,Simulate the future change process of runoff under different climate scenarios.The decline of water in the source of the Yellow River and the source of the Yangtze River showed different degrees of decline in different climate scenarios,and the decline in the source of the Lancang River only showed a downward trend in the SSP1-2.6 scenario.The temperature in the source area of the Three-River Headwaters Region all showed an upward trend,with different rising rates.The runoff at the source of the Yellow River and the source of the Yangtze River showed different degrees of decline,while the runoff at the source of the Lancang River only showed a significant decline in the SSP5-8.5 scenario.