|Timeline:||July 2016 - 30 June 2020|
Climate change could result in observably hydrological and ecological changes of underlying surface. As the highly sensitive region to climate change, Tibetan plateau had experienced a significant permafrost degradation since the mid 1950s. The shortening duration of seasonal ground freezing, the increasing thickness of active layer and mean annual ground temperature had been widely reported. Representing freezing/thawing process of permafrost is of great importance in cold region climate studies. However, it is full of challenges as both soil water and heat are necessary to be accurately captured. Although various models have been developed by diverse backgrounds of researchers, current land surface models still cannot accurately capture the onset of freeze-thaw cycles and the dynamics of active layer thickness. On the other hand, the groundwater flow exert a non-ignorable influence on the permafrost as the exchanges of water and heat, which make the modeling of freeze/thaw process of permafrost more complex.
In my study, STEMMUS model, Simultaneous Transfer of Energy, Momentum and Mass in Unsaturated Soil, would be extended to consider the soil freeze/thaw process. It is characterized as a multi-phase (liquid, water vapor, dry air, soil ice), high time resolution and vertical discretion resolution model. The thermal equilibrium assumption between phases was employed and the internal energy for each phase was considered in the energy balance equation. Furthermore, the groundwater flow model would be coupled to fully understand the physics of hydraulic and thermal dynamics in cold regions.
Laboratory experiment and field experiment would be scheduled to advance our knowledge of soil freeze/thaw process and then to demonstrate the validity of the proposed model. With the aid of experimental observing and numerical modeling, we are trying to answer the questions as below:
When exactly does the soil water freeze/thaw?
How does the active layer of Tibetan plateau behave under long-term climate change?
How does the groundwater affect the dynamics of permafrost?
Figure 1. The permafrost and ground ice in Tibetan Plateau. Image copyright EDD (CTA)