Coupled water flow and heat transport in frozen soils

尽管温度低于冰点，液态水仍然存在于冻土中，重要的土壤过程如养分循环在冰点以下的温度下活跃。在土壤水分平衡方面，季节性冻土的土壤霜深显著影响融雪向地表径流或土壤水分的分配，这可能在丰水年引起洪水或在干旱年减轻干旱。冻土瞬态土壤水分含量的精确测量和模拟是理解这一过程的环境意义和气候变化对这一过程影响的关键。因此，本研究的长期目标是：增加对冻土中耦合水流和热输运过程的理解，并在这些过程的测量方面发展最新技术。

Despite sub-freezing temperatures, liquid water is still present in frozen soils and important soil processes such as nutrient cycling are active at sub-freezing temperatures. With respect to the soil water balance, soil frost depths in seasonally frozen soils significantly influence the partitioning of snowmelt into surface runoff or soil moisture which may potentially cause flooding in wet years or mitigate drought in dry years. Accurate measurement and simulation of transient soil moisture contents in frozen soils is key to understanding the environmental significance of these processes and the influence of climate change on these processes. Therefore, the long-term objective of this research is: To increase understanding of coupled water flow and heat transport processes in frozen soil and develop the state of the art with respect to measurement of these processes. The short-term objectives of this Discovery Grant are to: 1) improve measurement accuracy of liquid water and ice content in frozen soils using time domain reflectometry (TDR) and dielectric sensors; 2) to better understand the relationship between the soil freezing curve, soil thawing curve and the soil moisture retention curve under thermal equilibrium and non-equilibrium and a variety of soil solution electrical conductivities; 3) to measure, in-situ, using TDR, the temperature-induced redistribution of soil water during soil freezing and thawing, and estimation of soil thermal properties as a function of SLWC and SIC using inverse procedures with a coupled soil water flow and heat transport model. This research will train 2 MSc and 2 PhD students and an undergraduate research assistant. Upon completion of their degrees, these students will have a unique understanding of soil dielectric, hydraulic and thermal properties as well as measurement and simulation of coupled soil water and heat flow processes. Recent reports from the International Panel on Climate Change (IPCC) predict significant changes in amount, timing and phase of precipitation on the Canadian Prairies. Most climate scenarios predict winter precipitation to increase by up to 10% but the amount of snow will decrease and the amount of rain will increase. The research in this proposal will contribute significantly to understanding and measurement of frozen soil water flow and heat transport processes in frozen soils which will aid in the development and calibration of coupled mass and energy transport models. These models will greatly increase our ability to predict the impacts of climate change (i.e. winter rain, mid-winter thawing events) on the soil water and energy balance which influence agriculture, C and N cycles, and stream flow.