积沙影响下伏冻土的水热耦合模型研究

Coupled hydrothermal model of underlying permafrost influenced by sand accumulation

青藏高原地区冻土正呈退化趋势,除气候变化、人为活动的影响外,沙漠化也被认为是冻土退化的原因之一,但仍存在较大争议。基于不饱和土渗流和热传导理论,结合CoLM和CoupModel模型,初步构建了积沙-冻土-水热概念模型和耦合模型。并在两模型的基础上,讨论了沙层反射率、积沙体热容量、积沙体厚度和沙的传热率等参数对下伏冻土的热影响过程。结果表明,沙层的反射率、地面发射率均高于天然地表,沙层接受的热量较天然地表偏少;积沙地表下的沙层和活动层能截留更多热量,使冻结层获得的热量相对减少;沙的导热性较差,导致积沙地表下地温变化出现延迟,从而延缓冻土退化;同时,积沙无论厚薄,都将起到延缓冻土退化的作用。因而,沙漠化对青藏高原冻土退化的影响可能较小,但全面揭示沙漠化对冻土的影响仍需深入研究。

The desertification process, with great controversy, is considered to be one of the main reasons to per-mafrost degradation in Qinghai-Tibet Plateau apart from the influence by climate change and anthropic activities. Previous contestable views include .. （ 1 ） sand deposition accelerating permafrost degradation; （2） thin sand layer protecting permafrost while thick sand layer degrading permafrost; （3） sand accumulation protecting underlying permafrost regardless of its thickness. Though field investigations and laboratory simulative experiments have been carried out, it is still unclear what the influence mechanism between sand deposition and underlying perma- frost is. This research developed a preliminary conceptual model and coupled hydrothermal modelbased on soil hydrothermal processes and also referred to two primitive models including CoLM and CoupModel. Importantly, these models contribute greatly to well understanding the influence mechanism of underlying permafrost covered by sand. Based on the two models, later analyses on the stability of underlying permafrost influenced by multi pa- rameters of sand layer, such as reflectivity, thermal capacity, thickness and its thermal conductivity were carried out. Most of the analyses are qualitative descriptions and comparisons based on the conceptual model owing to the lack of data support. The energy caughtby sand layer is less than that in natural surface owing to the higher re- flectivity and emissivity of sand layer.At the meantime, permafrost layer obtainedless thermal energybecause more energy was reserved by sand layer and the thermal conductivity was poor under sand covering surface, re- sulting in a delay of permafrost degradation. Additionally, sand layer would postpone permafrost degradation pro- cesses in spite of how thick the sand layer is. In conclusion, desertification should not be reckoned as the main reason of permafrost degradation in the Qinghai-Tibet Plateau, andmore attention should be paid on climate change andanthropic activities. In addition, the conceptual and physical models in this paper are innovated origi- nally regarding to the stability of underlying permafrost influenced by sand covering, and it is also a creative idea that the physical model combines two common land process models. More endeavor need to be carried out on the further improvement of the physical model and numerical simulation and combination of the field observations and indoor laboratory experiments, to better understand the whole process of desertification and permafrost degra- dation. This research is meaningful in revealing the relationship between permafrost degradation and desertifica- tion, andcan provide references for the construction of important engineering projects passing sandy-permafrost belts on the Qinghai-Tibet Plateau or other similar areas.