Numerical simulations of permafrost dynamics and water cycle interactions
Arctic environments are expected to undergo substantial changes following predicted warming of 2.2 to 8.3 °C within this century, according to the IPCC. Most dramatic for terrestrial ecosystems and society will likely be the loss of permafrost and associated changes in freshwater systems. Permafrost inhibits groundwater movement and thereby controls the distribution and flow pathways of water through the landscape. Moreover, the landscape distribution of water is in itself an important control of permafrost, as it influences thermal properties of the ground and can act as a conveyor of heat. Permafrost and hydrology is thus best understood as a coupled system. In this project field experiments are combined with numerical modelling for coupling thermal and water fluxes for understanding future changes in this system. Specifically, the project will target the effects from groundwater on permafrost thaw rates, and future changes in groundwater and stream temperatures. The objectives of the project are: 1) To quantify the role of different heat transfer processes under various environmental conditions in terms of permafrost distribution, climate, terrain, and soil types. Specifically, the importance of groundwater as a transferor of heat will be studied, as these associated processes are not represented in traditional permafrost models. 2) To investigate the influence from permafrost dynamics, mainly seasonal and long-term thawing, on groundwater and river temperatures. 3) To quantify influence from different environmental and climatic drivers for future changes in permafrost distributions. The main tool for the numerical modelling experiments within this project will be the Arctic Terrestrial Simulator (ATS), which is a parallel code allowing for large-scale simulations. The ATS is a physically-based approach to model permafrost and seasonal frozen ground dynamics using a three-phase model of thermal hydrology, including conducted and advected heat fluxes. We will set up simalations for exploring thaw rates of sporadic permafrost following changes in soil moisture and snow cover. These simulations are based on field data collected in northern Sweden, as well as IPCC CMIP scenarios for future changes in climatic variables. The use of such realistic input data and domain setup is novel for numerically modeling coupled changes in hydrology and permafrost. Furthermore, we will simulate the impact of permafrost, seasonal freezing, and ground temperature cycles on groundwater discharge and temperture in alpine permafrost environments. Specifically we will focus on diurnal cycles in discharge and temperature on hillslopes of contrasting aspects. These simulations will be based on an extensive data set of hydrologic variables from northern Alaska. Future changes in hydrology and permafrost have the potential to critically impact fire and erosion regimes, and to alter habitat for fish and migratory birds. Arctic communities are dependent on freshwater and permafrost for livelihoods, through fishing and drinking water, and infrastructure. Moreover, future changes in these systems are of interest for the global community as they have potential impacts on the global carbon cycle. The outcome of this project could therefore be of value for planning mitigation and adaptation strategies to future changes in the Arctic.