River and lake ice are key components of cold-region freshwater systems. Their seasonal formation, growth, movement and decay influence river hydraulics and flood risk, lake heat budgets and mixing, sediment transport, ecosystems, infrastructure, hydropower, winter transportation and public safety. In rivers, frazil production, ice transport, accumulation and ice-jam formation can modify flow conditions and water levels. In lakes, the timing, duration, thickness and properties of ice cover control exchanges of heat, light and momentum between water and atmosphere.
Freshwater ice processes result from interactions among atmospheric forcing, hydrology, hydraulics, thermodynamics, ice mechanics and snow conditions. Climate-driven changes in air temperature, precipitation, snow cover, discharge and water temperature are altering freeze-up, ice-cover development and breakup, creating new challenges for prediction and risk assessment.

Modelling freshwater ice remains difficult because processes are strongly coupled, span multiple spatial and temporal scales, and differ between rivers and lakes. Model development and evaluation are further limited by sparse observations of ice thickness, concentration, velocity, roughness, snow-on-ice conditions, ice extent, thermal structure and ice jams, introducing uncertainty into calibration, validation and forecasting.

Recent advances in observations and computation provide new opportunities, including 1D, 2D and 3D models; thermodynamic and dynamic ice models; coupled atmosphere–hydrology–hydraulics–ice and lake-ice frameworks; data assimilation; uncertainty analysis; and machine learning. In-situ sensors, cameras, UAVs and remote sensing, including optical and radar imagery and satellite altimetry, also improve characterization of ice conditions and model evaluation.

This session invites contributions on river- and lake-ice processes, observations and modelling, including ice formation, growth, decay and breakup; freeze-up and breakup phenology; snow–ice interactions; frazil production and transport; ice jams and ice-induced flooding; lake-ice thickness, extent, thermal dynamics and stability; interactions among ice, flow, temperature, sediment and ecosystems; model development, coupling, calibration and validation; data assimilation, uncertainty quantification, probabilistic forecasting and machine learning; and operational applications for water management, infrastructure safety, hydropower and climate adaptation.