  The microstructure of snow determines its fundamental properties such as the
mechanical strength, reflectivity, or the thermo-hydraulic properties. Snow
undergoes continuous microstructural changes due to local gradients in
temperature, humidity or curvature, in a process known as snow metamorphism. In
this work, we focus on wet snow metamorphism, which occurs when temperature is
close to the melting point and involves phase transitions amongst liquid water,
water vapor, and solid ice. We propose a pore-scale phase-field model that
simultaneously captures the three relevant phase-change phenomena: sublimation
(deposition), evaporation (condensation), and melting (solidification). The
phase-field formulation allows one to track the temperature evolution amongst
the three phases and the water vapor concentration in the air. Our three-phase
model recovers the corresponding two-phase transition model when one phase is
not present in the system. 2D simulations of the model unveils the impact of
humidity and temperature on the dynamics of wet snow metamorphism at the pore
scale. We also explore the role of liquid melt content in controlling the
dynamics of snow metamorphism in contrast to the dry regime, before percolation
onsets. The model can be readily extended to incorporate two-phase flow and may
be the basis for investigating other problems involving water phase transitions
in a vapor-solid-liquid system such as airplane icing or thermal spray coating.
