IArctic land surface hydrology influences on regional and hemispheric temperature and circulation responses

Global warming is expected to have a stronger impact on the Arctic than on the rest of the globe, not only due to interactions between sea ice, snow, and radiation, but also because of the presence of permafrost. These soils store large amounts of carbon (around 1100–1700 Gt), which, if thawed, can affect the carbon cycle, soil hydrology, and surface energy exchanges. Accurately representing soil hydro-thermodynamic processes is therefore essential for realistically simulating Arctic climate change. However, limitations in the representation of soil processes and resolution in land surface models (LSMs) within Earth System Models (ESMs) lead to large uncertainties, for instance leaving it unclear whether the Arctic will become wetter or drier under future warming.

In this study, we use a modified version of the Max Planck Institute for Meteorology ESM (MPI-ESM) in which key thermodynamic and hydrological processes are enhanced particularly in permafrost regions. By tuning model parameters, we generate two idealized set-ups that create wetter and drier soil conditions in permafrost regions and that allow for testing the sensitivity to soil thermo- and hydrodynamics. Based on these configurations, we produce an ensemble of simulations, referred to as the Permafrost Physics Ensemble (PePE), covering the historical (1850-2014) period and extended up to 2300 CE under multiple climate change scenarios.

Our results show that differences in Arctic soil hydrology affect surface energy partitioning and consequently, permafrost extension, near-surface temperature, snow cover and sea ice fraction. Changes in soil moisture modify the background climate state and the strength of feedbacks related to snow and sea ice, contributing to Arctic amplification (AA). In our simulations, AA converges to a warming factor of about 2–3 when external forcing dominates over internal variability. Furthermore, these changes influence the large scale latitudinal gradient and Northern Hemisphere circulation variability by modulating patterns like the Arctic Oscillation (AO).