Changes in travel times in thawing permafrost systems

Physically based models for permafrost-hydrological interactions can contribute to improved process understanding and aid in bridging the gap between limited field observations and large scale heat, water and material transport effects. Previous studies have demonstrated the importance of including coupled heat and multiphase flow processes in order to better understand and describe the dynamics of permafrost change and its interactions with temperature and subsurface water conditions in partially frozen ground. In particular, long-term simulation results show that warming trends reduce the temporal and seasonal variability characteristics of groundwater and its discharges into surface waters.

A compelling question for waterborne transport of substances relevant for climate feedbacks, biogeochemical cycling and/or water pollution is how different scenarios of hydro-climatic change influence permafrost formation and degradation dynamics and through that also the residence times of subsurface water, from land surface recharge to surface water discharge. In this contribution, heat transport and water flow in permafrost systems which include the active layer are simulated and changes in water fluxes and associated travel times of water parcels through the subsurface are investigated. Initial results indicate that the geological setting can notably impact the spread and change in travel time distributions during warming. Also, for all cases investigated the median and minimum travel times increase, indicating longer flow pathways as permafrost thaws. Potential effects on solute transport and climatic feedbacks are highlighted.