Most land surface models (LSMs) used in climate models do not perform well in modeling the permafrost processes. Due to the complex permafrost distribution characteristics and landscapes of the Qinghai-Tibet Plateau (QTP), the LSMs simulations over QTP are even worse. In this study, we revised the permafrost scheme in the original Common Land Model (CoLM) to improve its capability of simulating permafrost processes. We adopted a new frozen soil parameterization scheme, in which maximum unfrozen water content is defined as a function of soil matric potential. In addition, we extended the model's bottom to a depth below that without annual variations in temperature and replaced the zero-flux lower boundary condition with a constant geothermal heat flux based on literature and temperature gradient measurements in a 34.5-m-deep borehole. What's more, we revised the original snow cover fraction parameterization scheme of CoLM according to the special snow cover distribution characteristics over QTP. We calibrated and validated the modified model against observations from 2005 to 2008. The results indicate that the modified model produced more reasonable simulations of radiation balance components and significantly improved the simulation of soil liquid water content. It also shows an improved capability of reproducing soil temperatures from the top to the bottom of soil layers. The modified CoLM provides a useful tool for understanding and predicting the fate of permafrost in QTP under a warming climate. (C) 2012 Elsevier B.V. All rights reserved.

使用CoLM模型,以青藏高原冰冻圈观测研究站设在唐古拉综合观测场的气象资料作为驱动资料,在青藏高原多年冻土区的唐古拉地区开展了单点模拟试验。通过和该站点同期实测资料对比发现:CoLM模型对高原多年冻土区的辐射通量各分量的模拟效果较好;对潜热通量的模拟误差较大,感热和地表热通量的模拟相对较好;模型能够很好地模拟活动层浅层土壤温度,但随着深度加深,模拟的温度较观测值有所低估。研究表明CoLM模型能较好地模拟多年冻土区地表与大气的能水交换过程,对其进行一些适应性改进后将能得到更好地应用。改进模型的土壤水热参数化过程尤其是添加未冻水参数化方案是将其应用到冻土区首先要解决的问题;再者扩展模型的模拟深度也十分必要。