CMIP5耦合模式对青藏高原冻土变化的模拟和预估

Evaluation and Projections of Permafrost on the Qinghai-Xizang Plateau by CMIP5 Coupled Climate Models

利用第五次耦合模式比较计划(CMIP5)多个模式的模拟结果,对比再分析资料和青藏高原(下称高原)冻土图,评估了模式对当前(1986-2005年)高原冻土的模拟能力。在此基础上应用多模式集合平均结果,预估了未来不同典型浓度路径(RCPs)情景下高原地表层多年冻土的可能变化。结果表明:CMIP5耦合模式对高原冻土有一定的模拟能力,采用SFI地面冻结指数模型计算的当前地表层多年冻土分布与高原冻土图有较好的吻合,1986-2005年高原地表层平均多年冻土面积为127.5×10~4km^2;多模式集合预估结果显示,高原地表层多年冻土呈现区域性退化趋势,高原东部、南部及北部边缘地区冻土带退化较为明显,有从外围向西北部多年冻土区逐步退化的趋势,RCP2.6、RCP4.5、RCP6.0和RCP8.5情景下未来50年地表层多年冻土面积分别减少约23.9×10~4km^2(20.8%)、33.5×10~4km^2(27.7%)、25.6×10~4km^2(21.1%)和43.5×10~4km^2(35.3%),到21世纪末期不同情景下多年冻土面积分别约为为91.4×10~4km^2、70.9×10~4km^2、72.8×10~4km^2和41.7×10~4km^2。

As an important forcing factor of the land surface, permafrost is very sensitive indicator of climate change. The freeze-thaw process is directly involved in local energy and water cycles, and in turn affects weather and climate. In this study, using the multi-model results from the fifth phase of the Coupled Model Intercompari- son Project （CMIP5）, we computed the near-surface permafrost area on the Qinghai-Xizang Plateau （QXP） via surface frost index （SFI） method, and assessed the ability of models to simulate the related climate variables and present-day （ 1986 - 2005） permafrost, by comparing with the reanalysis products and the frozen soil map of the QXP. Based on this assessment, the climate models were aggregated by arithmetic mean to project the changes of permafrost on the QXP under the four different Representative Concentration Pathways （RCPs）. The results show that the CMIP5 coupled models have some simulation capabilities for permafrost on the QXP. The simulat- ed present-day near surface permafrost distribution is similar to the plateau frozen soil map, with the annual aver- age of permafrost area of 127.5 × 10^4 km2 （ 1986 - 2005）. The prediction results by multi-model ensemble mean indicate that the permafrost appear a degradation tendency on the QXP, especially on the eastern, southern and the edges of northern plateau. The permafrost will shrink from the edges to the north-west inner part of the QXP, and most probably exist only in the northwestern regions by 2099. Using the SFI method, the rate of the perma- frost area change under RCP2.6, RCP4. 5, RCP6. 0 and RCP8.5 scenarios are - 2.2× 10^4 km2 （10a）-1, - 5.9× 10^4 km2 （10a）-1, - 5.4× 10^4 km2- （10a）-1 and -10. 0× 10^4 km2.（10a）-1, respectively. In the next 50 years, the permafrost area will decrease abont 23.9×10^4 km： （20. 8%）, 33.5×10^4 km2 （27.7%）, 25.6×10^4 km2 （21. 1%） and 43.5x×10^4 km2 （35.3%） under RCP2.6, RCP4.5, RCP6.0 and RCP8.5, respectively. The average values of permafrost area in the last period of 21st century are about 91. 4× 10^4 km2 （RCP2. 6） , 70. 9×10^4 km2 （RCP4. 5）, 72. 8× 10^4 km2 （RCP6.0） and 41.7× 10^4 km2 （RCPS. 5）. Although there are large ranges in degree of degradation for different scenarios, the linearity of relationship exist between the permafrost area and the sur- face air temperature.