| Water source analysis is one of the key tasks in the first phase of the "Study on Runoff Changes and Adaptive Utilization in the Source Region of the Southwest River".Scientific water source analysis is not only the basis for identifying the non-uniformity of runofif and the unsteady state of the water resources system,but also the key basis for the targeted and accurate multi-target regulation of water resources.It is the frontier and hotspot of international hydrology and water resources research.The water source type ofNaqu River Basin is diverse,the spatial combination characteristics are complex,and the change is more significant.The high dependence of vegetation on water can provide an important basis for the analysis of water source and the verification material.Because of the small influence of human activities,the basin is an ideal area for water source analysis subject to natural variation conditions.Based on the combination of experiment and model simulation,this paper draws the following conclusions on water source analysis:The connotation of water source analysis is to target users with difrferent natural or social attributes,and to analyze the user's water source type,composition,water age,and source materials by means of geographic information technology,model simulation and experiment.From a technical point of view,water source analysis includes qualitative analysis and quantitative analysis.Qualitative analysis is based on the classification of topography and geomorphology by means of natural geographical features.On this basis,the water source type analysis of the geomorphic unit is carried out;quantitative analysis is to quantitatively identify the composition and evolution of water sources in different landform types by simulating the water cycle process of the basin by means of hydrological model.The analysis of the evolution law of the 500mm rainfall contour and the 2000°C accumulated temperature contour in the Nagqu Prefecture shows that the 500mm annual precipitation contour in the Nagqu Prefecture is on the interdecadal scale,which is slightly offset from the southeast in the 1970s.Afterwards it has been shifted to the northwest.The 500mm annual precipitation contour shows a trend of migration to the west and south in the meridional and latitudinal directions respectively;the transformation period of the center point in the warp direction is 3.3 years,and the transformation period in the latitude direction is 7.1 years;Mutations occurred around 1996,and there was no mutation in the latitude.The 2000 ? accumulated temperature contour in the Nagqu Prefecture showed an offset to the northwest in the 1970s and 1980s on the interdecadal scale.It moved back to the southeast in the 1990s and continued to move southward after the 2000s.The 2000 ? accumulated temperature contour shows a trend of migration to the west and northward in the meridional and latitudinal directions,respectively,and the trend is not significant;the centerline coordinates exist in the menstrual direction in the main cycle of 2.8 years and the sub-period of 7 years,in the latitude There was no obvious period;the center point coordinate longitude was abruptly changed from 1966 to 1967,and the latitude was abruptly changed around 2005-2006.When in the same planting zone,the annual precipitation in the Nagqu Prefecture is generally higher than the national average of 17?129mm;while the accumulated temperature level is generally lower than the national average of 35?13380C,the same planting may be needed when growing in the alpine region.More precipitation and less accumulated temperature.When the isothermal line of accumulated temperature and precipitation is spatially displaced,the distribution of vegetation belts in the Nagqu Prefecture may be spatially redistributed.In order to correct the model input parameters,the double-ring infiltration experiment was carried out in the Naqu River basin.The experimental results show that the stable infiltration rate in the basin has obvious spatial distribution difference,and the stable infiltration rate in most areas is 2.56-4.88cm/h.Within the range,the stable infiltration rate in the middle of the basin,the downstream of the Lake and the source area of the basin is in the range of 4.89?7.2cm/h,and there is a small range of stable infiltration in the upper reaches of the basin,ranging from 7.3 to 11.3cm/h within the range,the stable infiltration rate in some areas downstream of the basin is the smallest at the level of the whole basin,which is 0.23?2.55cm/h.The main reason is that the ridgeline near the exit of the basin is higher,and more frozen soil is found during the experiment.The stable infiltration rate in this part of the region is small.The spatial distribution results of the stable infiltration rate were input into the water source analytical model,and the simulation accuracy of the model was found to be improved.By analyzing the simulation results of the water source type model,the composition of the water source type in the basin and the distribution during the year can be obtained:from the overall perspective of the basin,the average annual total runoff of the Naqu River basin during the period 1979-2013 is 3.28 billion m3,of which the glaciers and The snowmelt runoff flow accounts for 8.85%and 21.36%of the total runoff of the basin respectively.The total runoff,glacier runoff and snowmelt runoff in the basin show an increasing trend.The percentage of snow runoff to the total runoff decreases.The glacial runoff accounts for the total runoff.The percentage is increasing.For different water source type terrain divisions,the water source composition of the whole year shows spatial differences with the changes during the year.Generally speaking,the water source types in the basin from November to April are mainly snowfall and groundwater recharge,snowmelt from May to June,from July to October,rainfall and snowfall supply are the mainstays. |
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