Effects of Different Initial Values on the Simulation of Permafrost Hydrothermal Processes at Xidatan Station on the Three-River Regions

Abstract

Different initial values have a profound impact on the simulation of the permafrost hydrothermal process.The observation data from the Xidatan Station in the permafrost region of the Three-river sources regions on the Qinghai-Xizang （Tibet） Plateau， CLM4.5 （Community Land Model version 4.5） is used to conduct 14 months simulation of the permafrost at the Xidatan Station.And design three experiments to test the simulation performance of CLM4.5 for permafrost， which explores the effects of initial soil temperature， initial liquid water content and initial ice content on the simulation results， and revise the calculation of initial soil ice content to improve the hydrothermal simulation ability of permafrost.Compare soil temperature， liquid water content and soil ice content between simulated and observed， the results show that the initial soil temperature and liquid water content in CLM4.5 will affect the simulation of the hydrothermal process of permafrost by affecting the initial ice content.The default initial soil temperature and liquid water content to calculate the initial soil ice content is 0 m3·m-3， which makes the model unable to accurately simulate the characteristics of permafrost.The soil ice content is greater than 0.01 m3·m-3 from the beginning of November 2015 to the beginning of August 2016 and is almost zero during the rest of the period.The soil liquid water content of the entire layer of soil begins to decrease in winter and increase in spring.The soil temperature below 2.8 m is greater than 0 ℃ throughout the year， and 0~2.8 m shows the characteristics of seasonally frozen ground with freezing in winter and thawing in summer.Modifying the initial soil temperature and liquid water content as observational values， the simulation results show the characteristics of permafrost.The soil ice content below 1.8 m is always greater than 0.01 m3·m-3.The soil liquid water content of above 1.0 m begins to decrease in winter and increases in spring， and below 1.0 m is 0~0.01 m3·m-3 throughout the year.The soil temperature below 2.8 m is below 0 ℃ all year round， and the active layer thickness is about 2.8 m， which overestimate about 115.4%.Based on modifying the default values as observed values， further， modify the calculation of initial soil ice content， so that the simulated soil ice content increases as a whole and the soil ice content below 1.1 m is always greater than 0.025 m3·m-3.The soil liquid water content of above 2.3 m is increased in summer and autumn and maintained at 0~0.1 m3·m-3 below 2.3 m.The active thickness layer decreased to 1.7 m， which overestimate about 30.8%， and significant improvement in soil temperature simulation of each layer.

Keywords

• permafrost
• clm4.5
• soil ice content
• soil liquid water content
• soil temperature