Arctic and subarctic environments are particularly sensitive and susceptible to climate change effects. In these cold-regions changes in surface and groundwater systems may strongly interact with changes in active layer thickness and permafrost extent. Moreover, understanding links between permafrost degradation and the release of carbon is crucial for the evaluation of key climate feedback mechanisms. However, model predictions are hampered by an incomplete understanding of the hydrological processes occurring during permafrost degradation that will control the fluxes of carbon and other constituents. This session aims to bring together research that reports on recent developments in the understanding of permafrost, hydrological, hydrogeological and transport processes, their interactions and changes under the influence of climate change. Studies investigating quantification of processes through modelling are especially welcome, as well as developments in using and applying available field data to model implementation and design.