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，在低于冰点的温度下是活跃的。在土壤水分平衡方面，季节性冻土中的土壤冻结深度显著影响融雪进入地表径流或土壤水分的分配，这可能会在丰水年引起洪水或在干旱年减轻干旱。冻土中瞬时土壤水分含量的精确测量和模拟是理解这些过程的环境意义以及气候变化对这些过程的影响的关键。因此，本研究的长期目标是：增加对冻土中耦合的水流和热传输过程的理解，并发展这些过程的测量技术。 本研究的短期目标是：1）提高利用时域反射仪（TDR）和介电传感器测量冻土中液态水和冰含量的准确性; 2）更好地了解热平衡和非平衡条件下土壤冻结曲线、土壤解冻曲线和土壤水分保持曲线与各种土壤溶液电导率之间的关系;（3）利用TDR原位测量土壤冻融过程中温度引起的土壤水分再分布，并利用耦合的土壤水热传输模型反演土壤热性质。 本研究将培养2名硕士生和2名博士生以及一名本科生研究助理。完成学位后，这些学生将对土壤介电，水力和热特性以及耦合土壤水和热流过程的测量和模拟有独特的理解。 国际气候变化专门委员会（IPCC）最近的报告预测，加拿大大草原的降水量、时间和阶段会发生重大变化。大多数气候情景预测冬季降水量将增加10%，但降雪量将减少，降雨量将增加。在这个建议中的研究将大大有助于理解和测量冻土中的水分流动和热量传输过程，这将有助于耦合质量和能量传输模型的开发和校准。这些模型将大大提高我们预测气候变化（即冬季降雨，冬季中期解冻事件）对土壤水分和能量平衡的影响的能力，这些影响农业，C和N循环和水流。

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.