Coupled water flow and heat transport in frozen soils

尽管温度低于冰点，但冻土中仍然存在液态水，在冰点以下的温度下，养分循环等重要的土壤过程是活跃的。在土壤水分平衡方面，季节冻土中的土壤霜冻深度显著影响融雪到地表径流或土壤水分中的分配，这可能会在多雨年份导致洪水或在干旱年份缓解干旱。准确测量和模拟冻土中的瞬时土壤水分含量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，这项研究的长期目标是：增加对冻土中水和热传输耦合过程的了解，并发展关于这些过程测量的最新技术。 该发现基金的短期目标是：1)利用时域反射仪(TDR)和介电传感器提高冻土中液态水和冰含量的测量精度；2)更好地了解土壤冻结曲线、土壤融化曲线和热平衡和非平衡状态下的土壤持水曲线以及各种土壤溶液电导率之间的关系；3)使用TDR现场测量土壤冻结和解冻过程中温度诱导的土壤水分再分配，并利用土壤水热耦合模型的反程序估计土壤热性质作为SLWC和SIC的函数。 这项研究将培养两名硕士和两名博士生和一名本科生研究助理。完成学位后，这些学生将对土壤的介电、水力和热学性质以及土壤水和热流耦合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，加拿大草原上的降水量、时间和阶段都将发生重大变化。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。该方案的研究将有助于理解和测量冻土中的水和热传输过程，这将有助于开发和校准耦合的质量和能量传输模型。这些模型将大大提高我们预测气候变化(即冬季降雨、仲冬融化事件)对土壤水和能量平衡的影响的能力，这些影响会影响农业、C和N循环以及溪流。

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.