A two‐directional freeze and thaw algorithm for hydrologic and land surface modelling

This paper presents a two‐directional Stefan's solution for computing the freeze and thaw of soil columns. Use of an inverted set of equations to drive the soil freeze‐thaw from the bottom is a significant improvement to the original freeze‐thaw model. Simulations using the algorithm compared well with the 0°C isotherm interpolated from observed data at Arctic, Subarctic and cool temperate sites with different frost conditions that range from permafrost to seasonal frost across a north‐south gradient in North America. The incorporation of explicit freeze‐thaw parameterization in hydrologic and land surface models would enable realistic simulation of soil temperature, soil moisture and runoff/infiltration and hence energy, water and greenhouse gas exchange processes in high latitudes.