随着全球气候变暖,青藏高原冻土活动层正在逐渐加深,为了理解积雪和表层有机质土壤对冻土活动层的影响机理,一维水热耦合模型CoupModel被用于模拟气象驱动下土壤冻融的动态过程.基于祁连山冰沟和青藏高原唐古拉站长期监测数据,CoupModel模型被成功的率定和验证.在冰沟站验证的模型被用于研究积雪对冻土活动层的影响,结果显示:目前较浅积雪情景(雪深<20cm)比完全忽略积雪的情景模拟的冬季土壤冻结深度深,说明青藏高原现状下较浅的积雪有利于冻土发育.原因是雪面较高的反照率造成地表吸收的太阳辐射减少,导致雪面温度较低,加之浅雪的阻热性能又较小,综合导致浅雪覆盖时表层土壤向大气释放的能量增加.但随着积雪深度逐渐增加,模拟的冬季土壤冻结深度反而越来越浅,说明较厚的积雪(>20cm的雪深)并不利于冻土的发育,主要是雪相对于空气低的热传导隔绝了表层土壤向大气的热损失.在唐古拉站验证的模型被用于研究有机质土对冻土活动层的影响,结果显示:随着有机质土壤深度增加,模拟的活动层夏季融化深度逐渐较小.有机质土壤较矿物质土壤低的热传导和高的热容性质减少了下伏土壤热状况对太阳辐射和气温波动的响应,说明有机质土有利于冻土的保护.

The most important factors affecting the active layer depth and distribution of permafrost on the plateau are snow cover and thickness of the organic soil layer,except for air temperature and solar radiation.In this study,data from two typical field sites(Binggou Station and Tanggula Station) on the plateau were used.The two stations were established by the CAREERI,CAS to monitor the impact of snow cover and organic soil layer on the energy balance and thermal state within the active layer.In order to find the process-based explanations for the recent monitoring results,the one-dimensional heat and water flow model CoupModel was used to calculate the vertical heat and water fluxes in a soil-snow-atmosphere system for climatic conditions at the two field sites.The model was successfully adjusted and applied to simulate the active layer dynamics under a surface covered by snow and tundra soil conditions. Subsequently,the model was used to investigate the effects of snow cover and organic soil layer on the active layer. The investigation on the influence of snow cover on the active layer at Binggou Station revealed that snow cover depth is the key to the effect of snow cover on the active layer.The shallow snow cover (less than 20cm)is advantageous to frozen soil development. The thick snow cover in winter obviously insulates the subsoil against energy losses to the atmosphere.The frozen active layer depth is reduced and not conducive to the conservation of permafrost.Sensitivity study shows that the thawing depth of the active layer decreases with organic increasing.The organic layer makes the underlying soil less responsive to solar radiation and air temperature fluctuations,owing to its low thermal conductivity and high heat capacity,and thus provides a protection against permafrost thawing. Both influences are of importance for the behavior of permafrost under global warming.