| The widely distributed glaciers,snow,permanent and seasonal frozen soil in the cold plateau area affect the energy and hydrological cycle processes in the basin.In addition,the cold regions of the plateau have special climatic conditions,with thin air,strong solar radiation,and meteorological elements such as temperature and precipitation are greatly affected by elevation.The geological structure is also different from other regions.This area is not only widespread with glaciers,but also a unique geological structure formed during plate movement,which makes the hydrological cycle and energy process in the cold plateau area different from other areas.Under the background of climate warming,the melting of glaciers and snow in alpine regions accelerates and the permafrost is degraded.Therefore,the water cycle and energy processes in the region are affected to varying degrees.But so far,the research on the water cycle process in the special environment of the plateau cold region still lags far behind other regions.Therefore,carrying out the research on the hydrological model in the special environment of the plateau cold region and discussing the evolution law of the watershed hydrological cycle under climate change has certain scientific and application value for a comprehensive understanding of the water cycle process in the region.At the same time,it is also the practical demand to ensure the rational development and utilization of water resources and hydropower energy in China.Based on this,according to the characteristics of various hydrological cycle elements in the plateau cold region,with the help of corresponding field experiments,a distributed hydrological model with complete physical mechanism suitable for the special environment of the plateau cold region was constructed,and based on this,the evolution process of inner diameter flow in the basin was analyzed.It supports the hydrological cycle research and efficient utilization of water resources in the region.The main research contents and conclusions of this article are as follows:1.Aiming at the water cycle process under the special underlying surface conditions in the cold plateau,a systematic field experiment was carried out to clarify the water and heat transfer process and the hydrological response process under the typical underlying surface conditions.The basic physical parameters and hydrothermal kinetic parameters of the typical underlying surface had been determined experimentally.And around the water and heat migration process of the underlying surface profile and the water phase transformation process,the soil water,heat,potential energy changes,and the basin meteorological and runoff processes were dynamically monitored.Through the equilibrium analysis of the water and heat flux,the law of water and heat transfer and the hydrological response relationship in the freezing and thawing process under the typical underlying surface conditions in the cold plateau of the plateau were clarified.It provided a data basis for revealing the coupling mechanism of energy and water in the freezing and thawing process and the construction and verification of the distributed hydrological model in the cold plateau area.2.Based on the geological characteristics of the Qinghai Tibet Plateau with thin soil above and thick gravel layer below,and considering the widely distributed snow in the basin,a "snow-soil-sand-gravel" multi-layer water-heat coupling simulation method and "Soil-sand gravel" dual structure storm infiltration model were established for the cold plateau area.The new model divided a single soil structure into two types: soil layer and gravel layer,and added a snow layer on the soil layer.In the freez-thaw period,considering the blocking effect of snow on heat transfer,based on the soil-gravel structure characteristics,the water and heat transfer process was simulated in active and inactive areas.In the non-freeze-thaw period,considering the infiltration reduction of the upper soil and the effect of the fast passage of large pores in the lower sand and gravel,a "soil-sand gravel" dual structure storm infiltration model was established based on the multi-layer Green-Ampt model.The improvement of the simulation structure corrects the original model’s overestimation of the soil moisture content below the topsoil,reduces the temperature fluctuation and soil freezing and thawing speed of the surface soil simulation,and improves the overall accuracy of the model’s depiction of the soil freezing and thawing process in the region.(The moisture content RE decreased from 33.74% to-12.11%,and the temperature RE decreased from-3.60%to 0.08%).3.In view of the special radiation energy characteristics in the cold plateau area,starting from the atmospheric model,the calculation method of the radiation energy in the cold plateau area was improved,and the radiation energy characteristics in the cold plateau area and its influence mechanism on the hydrological process were discussed.Based on the non-linear change of the atmospheric model with altitude,the influence of plateau terrain and climate conditions on the radiant energy was quantified through the elevation,and the energy calculation method in this area was improved.The total radiation and net radiation calculation methods corrected by the atmospheric model have respectively corrected the underestimation and overestimation of the two radiant fluxes in the FAO model,and each radiant flux RE is less than 10%.On this basis,the proposed evapotranspiration simulation method suitable for the climatic characteristics of the cold plateau and the "snow-glacier" coupling simulation method simulates RE both less than 5%.The water cycle simulation process in the cold plateau area is improved in terms of energy and hydrological processes.4.Aiming at the geological,climatic,and landform characteristics of the cold plateau area,based on the WEP-COR model,coupling the "snow-soil-gravel" module and the energy hydrological response mechanism,a distributed hydrological model for the cold plateau area is constructed.Forming a WEP-QTP model reflecting the characteristics of the region.The simulation results of the Niyang River Basin show that.The newly constructed model improves the water and heat conduction process in the basin during the freezing and thawing period and the non-freezing and thawing period,extending the river groundwater replenishment time,and enhancing the regulation effect of groundwater on the runoff of the basin.The simulated daily flow process is basically the same as the actual flow process(Nash>0.75,| RE |<10%).5.Based on the constructed WEP-QTP model,the Niyang River Basin meteorology and drainage evolution law were analyzed,and the model-based multifactor attribution analysis method was used to reveal the driving mechanism of climate change on runoff evolution.From 1961 to 2018,the temperature,precipitation,and runoff of the Niyang River Basin increased significantly,and the change period of the three was about 27 years.The average annual flow had a sudden change in 1986,and the average annual flow increased by 26.78% after the sudden change.The increase in precipitation was the main reason for the increase in runoff in the Niyang River Basin.The increase in precipitation also increased the direct runoff and snowmelt runoff,which account for a relatively large amount of runoff.The two worked together to increase the runoff. |
