气候变化条件下青藏铁路沿线多年冻土概率预报(Ⅰ):活动层厚度与地温

Probabilistic Prediction of the Impacts of Climate Change on Permafrost Stability along the Qinghai-Tibet Railway(Ⅰ): Active Layer Thickness and Ground Temperature

对1961—2100年IPCC气候模拟与预测结果进行降尺度处理,得到铁路沿线空间分辨率为1km、时间分辨率为1h的大气边界条件.对铁路和公路沿线钻孔资料在垂直和水平两个方向进行空间差值处理,得到水平1km、垂直0.1m分辨率的沿线地下含水(冰)量的二维分布,作为初始条件.考虑气候模型预测误差和空间格网内地形的变化,以Monte Carlo方法产生气温的概率分布,以此作为冻土模型的驱动.对公共陆面过程模型(CoLM)的土壤分层进行细化,使得模型更为细致地模拟多年冻土地表及活动层的水热交换过程.在此基础上,模拟过去40a和未来100a铁路沿线多年冻土路段1km分辨率的活动层厚度概率预报结果,根据沿线观测和考察数据进行分区验证.结果表明:模拟的活动层厚度可以反映出不同分区的异同,但是模拟的活动层厚度总体偏小.根据青藏高原1961—2002年土壤表层温度(0cm)和2006年铁路沿线土壤温度观测廓线数据进行验证,发现表层和浅层土壤温度相对误差较小,而深层土壤温度相对误差较大.

In this paper,permafrost prediction（active layer thickness and ground temperature） along the Qinghai-Tibet Railway（QTR） by probabilistic method is presented.The atmospheric boundary conditions are obtained from IPCC climate simulation and forecast from 1961 to 2100 by using dynamical and statistic downscaling methods.The initial conditions of ground water content（ice content） are obtained from boreholes along the QTR and the Qinghai-Tibet highway by spatial interpolation method.Owing to the uncertainties of the climatic model forecasting and the topographic variation within the model grid,air temperature time series are perturbed by Monte Carlo method to implement ensemble forecasting.The common land model（CoLM） with a more detailed layering scheme is adopted to simulate and predict the exchange of energy and water within the active layer along the QTR. The active layer thickness in the past 40 years and in the future 100 years are validated by field surveys in all 14 subareas along the QTR,and the validation suggests that the simulation can describe the profiles of active layer thickness in different subareas.However,the comparison with the observations in several periods shows that the active layer thickness is generally underestimated.Besides,the simulated soil temperatures are compared with both ground surface temperatures（0 cm） at meteorological stations during 1961—2002 and soil temperature profile measurements at the 44 boreholes in 2006.The comparison suggests that errors at the surface and shallow layers are smaller than that in deep layers.The relative accuracy is 71.79% and 26.27% at the surface（0 cm） and at the depth of 2 m,respectively.