【作者】 李飞；

【导师】 张世强；

【作者基本信息】 西北大学 ， 地图学与地理信息系统， 2021， 硕士

【摘要】 多年冻土是冰冻圈的重要组成部分,多年冻土活动层水热过程的准确模拟对于理解和预估冰冻圈变化对水资源和生态的影响具有重要意义。陆面水文模型是目前模拟多年冻土水热过程的重要手段之一,土壤的导热率和未冻水含量是多年冻土水热过程模拟中的两个关键参数,其对模拟结果具有重要影响。本研究在已增加了冰川模块的VIC-CAS(Variable Infiltration Capacity-Chinese Academy Science)模型的基础上,分别用EBM(Enphy-Based Model)模型的土壤导热率方案替换VIC-CAS模型中的导热率方案,用CLM5.0(Community Land Model 5.0)模型的未冻水方案替换VIC-CAS模型中的未冻水方案,利用长江源区沱沱河站的连续观测数据进行了数值模拟对比试验,对比分析了不同的导热率和未冻水方案对活动层土壤不同深度(20、40、60、80、100、130和160cm)的热通量、温度和三层土壤(0～10cm、10～60cm、60～160cm)的含冰量、湿度等分量的影响。主要结论如下:(1)通过对比VIC-CAS原导热率方案和EBM导热率方案各分量的模拟结果,发现替换EBM导热率方案对土壤热通量、温度以及融化深度和速率的模拟结果影响较大,对土壤含冰量和湿度模拟结果影响较小。在土壤热通量模拟上,7个深度处EBM导热率方案对土壤热通量模拟值均低于VIC-CAS导热率方案,两者的差值在20cm深度土壤处最大,随深度增加而递减。在土壤温度模拟上,根据两种导热率方案模拟值与观测值间的纳什系数(NSE)和均方根误差(RMSE),20～60cm深度,模拟结果优于原方案;80～160cm深度,模拟结果差于原方案。在土壤含冰量模拟上,替换EBM导热率方案后表层和中层土壤的含冰量模拟差异不明显,下层土壤在冻结期的含冰量模拟值低于原方案。在土壤湿度模拟上,EBM导热率方案对表层和中层土壤的湿度模拟影响较小,下层土壤的湿度模拟值高于VIC-CAS导热率方案,与观测值间的NSE减小,模拟效果变差。在融化深度和速率上,相较原方案在夏季融化期模拟的融化深度速率降低,最大融化深度减小,但更接近观测值。(2)通过对比VIC-CAS原未冻水方案和CLM5.0未冻水方案各水热分量的模拟结果,发现替换CLM5.0未冻水方案对土壤热通量、温度以及融化深度和速率的模拟结果影响较小,对土壤含冰量和湿度模拟结果影响较大。在土壤热通量模拟上,7个深度处两者的热通量差异不明显,仅在20～40cm深度土壤的冻结期稍有不同。在土壤温度模拟上,两种未冻水方案对土壤温度和热通量的模拟趋势一致,与观测值间的NSE和RMSE接近。在土壤含冰量模拟上,CLM5.0未冻水方案在表层和中层土壤的含冰量模拟值均高于原方案,下层土壤的含冰量模拟结果变化不大。在土壤湿度模拟上,CLM5.0未冻水方案在三层土壤的湿度模拟值均低于VIC-CAS未冻水方案的模拟结果,下层土壤湿度模拟差异小于表层和中层土壤。表层和中层土壤湿度模拟效果变差,但下层土壤的模拟效果优于原方案。在融化深度和速率上,替换CLM5.0未冻水方案对土壤融化过程影响较小,融化深度和速率与原方案的差异较小,与观测值的误差较大。综合来看,VIC-CAS中的导热率和未冻水方案的模拟效果较为稳健。本研究中对导热率和未冻水不同方案的对比实验为进一步改进VIC-CAS模型中多年冻土水热模拟过程的相关方案提供了借鉴。更多还原

【Abstract】 Permafrost is an important part of the cryosphere,accurate simulation of the hydrothermal process in the active layer of permafrost is of great significance for understanding and predicting the impact of changes in the cryosphere on water resources and ecology.The land surface hydrological model is currently one of the important methods for simulating the hydrothermal process of permafrost.The thermal conductivity and unfrozen water content of the soil are two key parameters in the simulation of the hydrothermal process of permafrost,which have an important influence on the simulation results.In this study,on the basis of the VIC-CAS(Variable Infiltration Capacity-Chinese Academy Science)Model that has added the glacier module,the soil thermal conductivity scheme of the EBM(Enphy-Based Model)is used to replace the thermal conductivity of the VIC-CAS Model,the unfrozen water scheme of the CLM5.0(Community Land Model 5.0)to replace the unfrozen water scheme of the VIC-CAS Model,and use the continuous observation data of the Tuotuo River Station in the source area of the Yangtze River to carry out a numerical simulation comparison experiment.Analyzed the heat flux,temperature of different depths(20,40,60,80,100,130 and 160cm)and ice content,moisture of three-layer soil(0～10cm,10～60cm,60～160cm)of the active layer and other components with different thermal conductivity and unfrozen water schemes.The main conclusions are as follows:(1)By comparing the simulation results of each component of the VIC-CAS original thermal conductivity scheme and the EBM thermal conductivity scheme,it is found that replacing the EBM thermal conductivity scheme has a greater impact on the simulation results of soil heat flux,temperature,melting depth and rate,and has have little effect on the simulation results of soil ice content and moisture.In terms of the soil heat flux simulation,the EBM thermal conductivity scheme at 7 depths has a lower simulated value of the soil heat flux than the VIC-CAS thermal conductivity scheme.The difference between the two scheme is the largest at a depth of 20 cm,and it decreases with the increase of depth.In terms of the soil temperature simulation,according to the Nash coefficient(NSE)and root mean square error(RMSE)between the simulated value and the observed value of the two thermal conductivity schemes,the depth of 20～60cm,the simulation result is better than the original scheme;the depth of 80～160cm,the simulation result is worse than the original scheme.In terms of the simulation of soil ice content,after replacing the EBM thermal conductivity scheme,the difference between the simulated ice content of the surface and middle soil is not obvious,and the simulated ice content of the lower soil during the freezing period is lower than the original scheme.In terms of the soil moisture simulation,the EBM thermal conductivity scheme has little effect on the moisture simulation of the surface and middle soil.The moisture simulation value of the lower soil is higher than that of the VIC-CAS thermal conductivity scheme,and the NSE between the observed value and the simultated value is reduced,and the simulation effect becomes worse.In terms of melting depth and rate simulation,compared to the original scheme,the simulated melting depth rate and the maximum melting depth is reduced during the summer melting period,but it is closer to the observed value.(2)By comparing the simulation results of the water and heat components of the original VIC-CAS unfrozen water scheme and the CLM5.0 unfrozen water scheme,it is found that replacing the CLM5.0 unfrozen water scheme has a greater impact on the simulation results of soil ice content and moisture,and has have little effect on the simulation results of soil heat flux,temperature,melting depth and rate.In terms of the simulation of soil heat flux,the difference in heat flux between the two scheme at 7 depths is not obvious,only slightly different in the freezing period of the soil at the depth of 20～40cm.In terms of the soil temperature simulation,the two unfrozen water schemes have the same simulation trends for soil temperature and heat flux,which are close to the NSE and RMSE between the observations.In terms of the simulation of soil ice content,the simulated ice content of the CLM5.0 unfrozen water scheme in the surface and middle soil is higher than that of the original scheme,and the simulation results of the ice content of the lower soil have little change.In terms of the simulation of soil moisture,the simulated values of the three-layer soil moisture of the CLM5.0 unfrozen water scheme are all lower than the simulation results of the VIC-CAS unfrozen water scheme and the simulated difference of the lower soil moisture is smaller than that of the surface and middle soils.The simulation effect of surface and middle soil moisture has become worse,but the simulation effect of the lower soil is better than the original scheme.In terms of the melting depth and rate simulation,replacing the CLM5.0 unfrozen water scheme has less impact on the soil melting process,and the melting depth and rate are less different from the original scheme,and have a larger error with the observed value.Taken together,the simulation effect of the thermal conductivity and unfrozen water scheme in VIC-CAS Model is relatively robust.In this study,the comparative experiments of different schemes of thermal conductivity and unfrozen water provide a reference for further improving the relevant schemes of the permafrost hydrothermal simulation process in the VICCAS model.更多还原