不同初始值对多年冻土水热过程的模拟有着深刻的影响。本文利用青藏高原三江源多年冻土区西大滩站观测数据，驱动通用陆面模式CLM4.5（Community Land Model version 4.5）对该站多年冻土进行为期14个月的模拟研究。设计三组试验，检验CLM4.5模式对多年冻土模拟性能，探究不同初始土壤温度、液态水含量以及含冰量对模拟结果的影响，并对土壤初始含冰量的计算进行改进，提高了模式对多年冻土水热过程的模拟。通过对比土壤含冰量模拟值，液态水含量和土壤温度观测值与模拟值，结果表明：（1）初始土壤温度、液态水含量会通过影响初始土壤含冰量进而影响CLM4.5模式对多年冻土水热过程的模拟。（2）CLM4.5默认初始土壤温度、液态水含量时，计算出的初始含冰量为0 m3·m-3，这使得模式不能准确模拟出多年冻土的特征。在2015年11月上旬至2016年8月上旬土壤含冰量大于0.01m3·m-3，其余时段土壤含冰量几乎为0 m3·m-3；整层土壤液态水含量从冬...

利用位于季节冻土区的中国科学院那曲高寒气候环境观测研究站那曲/BJ观测点的野外观测数据,通过CLM4.5的单点模拟实验,分析评估了Luo土壤热导率参数化方案、Johansen土壤热导率参数化方案、C?té土壤热导率参数化方案和虚温参数化方案对土壤温、湿度的模拟能力,为将来选取最优的参数及参数化方案来更合理的模拟青藏高原土壤冻融过程为目的的工作提供依据。结果表明:(1)三种土壤热导率参数化方案模拟结果的土壤热传导率有明显差异,其中C?té方案的土壤热传导率最高,Luo方案的土壤热传导率最低。(2)三种热传导率方案均能合理地模拟出土壤温湿度的日变化趋势,Johansen方案对土壤温度年变化趋势模拟的更好,C?té方案对土壤温度模拟的数值较观测值偏离的更小,Luo方案对土壤湿度的模拟更好。(3)加入虚拟温度方程,并引入相变效率参数后,减少了模式对土壤湿度模拟的负偏差,Y-L方案在保持土壤温度较好模拟能力的基础上,能够进一步的提升土壤湿度的模拟能力。

Changes in soil temperature (ST) and soil moisture (SM) are essential for climate change and ecosystem assessments. Previous investigations on the ST and SM on the Tibetan Plateau (TP) are mainly based on the situ observation and the satellite products. In this study, the improved Community Land Model version 4.5 (CLM4.5), with proper parameter optimization and surface datasets update, is used to estimate the response of ST and SM in the TP to climate change in the long-term time series from 1961 to 2010. After validating the reasonability of the simulated results using the observations, the spatial distribution of changes in ST and SM in annual and seasonal time series since 1960s, 1980s, 1990s, are investigated respectively and the changes of precipitation (Pr) and surface evaporation (Ev) are also analysed to understand the cause of changes objectively. As a whole, the soil was warming and wetting at the maximum value of 0.31 degrees C/decade and 0.77%/decade since the 1960s. However, the warming process in soil mainly occurred in the 1980s while the wetting tendency is detected since the 1990s extensively. Except for the influence of air warming, the enhanced Pr and Ev might also be indispensable factors that caused the intensive wetting process but damped warming process in soil. Summer is the favourable season for the thermal and hydraulic variation since the 1980s. There exists the striking warmer and drier trend in the eastern TP since 1980s while the colder and wetter condition in the western TP since the 1990s. The magnitude of variation in soil is magnified from 1990s under the continuing impact of climate change.

Numerical simulation is of great importance to the investigation of changes in frozen ground on large spatial and long temporal scales. Previous studies have focused on the impacts of improvements in the model for the simulation of frozen ground. Here the sensitivities of permafrost simulation to different atmospheric forcing data sets are examined using the Community Land Model, version 4.5 (CLM4.5), in combination with three sets of newly developed and reanalysis-based atmospheric forcing data sets (NOAA Climate Forecast System Reanalysis (CFSR), European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-I), and NASA Modern Era Retrospective-Analysis for Research and Applications (MERRA)). All three simulations were run from 1979 to 2009 at a resolution of 0.5 degrees x 0.5 degrees and validated with what is considered to be the best available permafrost observations (soil temperature, active layer thickness, and permafrost extent). Results show that the use of reanalysis-based atmospheric forcing data set reproduces the variations in soil temperature and active layer thickness but produces evident biases in their climatologies. Overall, the simulations based on the CFSR and ERA-I data sets give more reasonable results than the simulation based on the MERRA data set, particularly for the present-day permafrost extent and the change in active layer thickness. The three simulations produce ranges for the present-day climatology (permafrost area: 11.31-13.57 x 10(6) km(2); active layer thickness: 1.10-1.26 m) and for recent changes (permafrost area: -5.8% to -9.0%; active layer thickness: 9.9%-20.2%). The differences in air temperature increase, snow depth, and permafrost thermal conditions in these simulations contribute to the differences in simulated results.

A growing body of simulation research has considered the dynamics of permafrost, which has an important role in the climate system of a warming world. Previous studies have concentrated on the future degradation of permafrost based on global climate models (GCMs) or data from GCMs. An accurate estimation of historical changes in permafrost is required to understand the relations between changes in permafrost and the Earth's climate and to validate the results from GCMs. Using the Community Land Model 4.5 driven by the Climate Research Unit -National Centers for Environmental Prediction (CRUNCEP) atmospheric data set and observations of changes in soil temperature and active layer thickness and present-day areal extent of permafrost, this study investigated the changes in permafrost in the Northern Hemisphere from 1901 to 2010. The results showed that the model can reproduce the interannual variations in the observed soil temperature and active layer thickness. The simulated area of present-day permafrost fits well with observations, with a bias of 2.02x10(6)km(2). The area of permafrost decreased by 0.06 (0.62)x10(6)km(2)decade(-1) from 1901 to 2009 (1979 to 2009). A clear decrease in the area of permafrost was found in response to increases in air temperatures during the period from about the 1930s to the 1940s, indicating that permafrost is sensitive to even a temporary increase in temperature. From a regional perspective, high-elevation permafrost decreases at a faster rate than high-latitude permafrost; permafrost in China shows the fastest rate of decrease, followed by Alaska, Russia, and Canada. Discrepancies in the rate of decrease in the extent of permafrost among different regions were mostly linked to the sensitivity of permafrost in the regions to increases in air temperatures rather than to the amplitude of the increase in air temperatures. An increase in the active layer thickness of 0.009 (0.071)mdecade(-1) was shown during the period of 1901-2009 (1979-2009). These results are useful in understanding the response of permafrost to a historical warming climate and for validating the results from GCMs.