Simulation of water and heat processes of permafrost and seasonally frozen soil in the upper reaches of the Heihe River based on the SHAW model
Global climate warming causes permafrost to rapidly heat up and gradually degrade into seasonally frozen soil.There are significant differences between permafrost and seasonally frozen soil in terms of soil stabil-ity,water transport,and land-atmosphere interaction.Distinguishing between permafrost and seasonally frozen soil is essential due to their distinct hydrothermal dynamics,freeze-thaw behaviors,and sensitivities to climatic variables.This study is based on the coupled hydrothermal model(Simultaneous Heat and Water model,SHAW),taking Dashalong Station(permafrost)and Arou Station(seasonally frozen soil)in the Qilian Moun-tains in the upper reaches of the Heihe River as the research objects,to simulate soil temperature,moisture and soil freezing and thawing processes.The results show that the SHAW model exhibits great accuracy in simulat-ing hydrothermal processes at both types of frozen soil sites,but its overall performance is better at permafrost sites.Specifically,the average Nash efficiency coefficients of soil temperature and soil moisture at permafrost/seasonally frozen soil sites are 0.95/0.91 and 0.74/0.37.These findings underscore the SHAW model's height-ened efficacy in simulating permafrost environments,particularly evident in its more accurate representation of soil temperature dynamics.The mean biases in the simulation of soil temperature and soil moisture at permafrost and seasonally frozen soil stations were determined to be 0.56/-1.40℃,and-0.001/0.03 m3·m-3,respective-ly.Further examination of simulations pertaining to active layer thickness and the duration of ground surface freezing revealed relatively higher errors at permafrost station.Conversely,errors were comparatively minimal at permafrost station,evidenced by an average depth error of the active layer thickness of merely 10.6 cm and an average error rate of 3%,affirming the SHAW model's high precision in permafrost station simulations.Con-versely,seasonally frozen soil station demonstrated superior performance in simulating maximum frost depth,with a mean absolute error of 21.0 cm and an error rate of 12%.The overall error in surface freezing duration simulations at permafrost stations(9%)marginally exceeded that at seasonally frozen soil stations(8%).In ad-dition,the freezing and thawing processes are significantly different among different frozen soil stations.The av-erage freezing speed(6.75 cm·d-1)of the permafrost station during the simulation period is greater than that of the seasonally frozen soil station(1.33 cm·d-1),while the average melting speed(2.11 cm·d-1)is smaller than the seasonally frozen soil station(3.15 cm·d-1).Since the underlying permafrost layer of Dashalong Station serve as an"underground cold source",the seasonal fluctuation range of soil temperature in deep layers(below 80 cm)is smaller than that of seasonally frozen soil stations.The research conclusion can provide a reference for the study of the freeze-thaw differences between permafrost and seasonally frozen soil in the upper reaches of the Heihe River.
万方数据
维普
