中文摘要：

近50 a青藏高原湿化趋势显著,降雨变化导致地表能量平衡过程、活动层水分状况和水热输运过程改变。以青藏高原北麓河铁路路基试验段水分监测为基础,基于土壤–地表–大气能量平衡的冻土水–汽–热耦合模型研究在未来降雨变化情景下,降雨对冻土路基水热的影响机制与过程。结果表明：近6 a路基水分监测显示,虽然青藏高原年降雨量变化较大,夏季降雨引起土体表层水分短期显著波动,但长期路基含水量并未明显累积,路基蒸发、液态水与水汽运移显著;在未来湿化背景下,年降雨量增大导致地表潜热增大地表土壤热通量减小,降雨增大导致的热传导通量减小量比液态水对流热通量增大更大,人为冻土上限抬升;降雨增加缓解了路基工程对下伏多年冻土的热扰动,但降雨增加导致活动层水分累积,增大路基冻胀和融沉灾害风险。

英文摘要：

Changes of air temperature or rainfall will inevitably influence the embankment stability in permafrost regions. Previous studies focused mainly on the influence of air temperature on the thermal stability of the embankment,while the influences of rainfall on the embankment and the influencing mechanism have not been fully considerated. Moreover,the understanding on the role of rainfall is still controversial. Observed data showed that the rainfall increased significantly on the Qinghai—Tibet Plateau during the past 50 years. The increase in rainfall can result in the change of the thermal-moisture activity in the active layer,the near-surface energy and the mass budget. The in-site precipitation and moisture data within railway embankment been measured in Beiluhe permafrost station and the water-vapor-heat transport model established were used to predict the process and mechanism of influence of increasing rainfall on gravel embankment. Collected data indicated that rainfall in summer significantly affected the shallow moisture in short time. But the long-term water content was not affected by rainfall, the moisture evaporation and the liquid water and water vapor transfer in embankment occurred clearly. The increase in rainfall will increase the surface latent heat,lower the heat flux and temperature of surface soil,and raise the artificial permafrost table. The reduction of heat conduction caused by increased rainfall is greater than the increase of heat convection of liquid water. Therefore,the increase in rainfall can mitigate the process of permafrost degradation and will alleviate the thermal influence of embankment engineering on underlying permafrost. While,the increased rainfall infiltrations will result in the increase of water content in embankment and induce the frost heave and thawing settlement.