Consequences of permafrost degradation for Arctic infrastructure – bridging the model gap between regional and engineering scales
Authors: Schneider von Deimling Thomas , Lee Hanna , Ingeman-Nielsen Thomas , Westermann Sebastian , Romanovsky Vladimir , Lamoureux Scott , Walker Donald A. , Chadburn Sarah , Trochim Erin , Cai Lei , Nitzbon Jan , Jacobi Stephan , Langer Moritz 
Published: May 2021

Abstract. Infrastructure built on perennially frozen ice-rich
ground relies heavily on thermally stable subsurface conditions. Climate-warming-induced deepening of ground thaw puts such infrastructure at risk of
failure. For better assessing the risk of large-scale future damage to Arctic
infrastructure, improved strategies for model-based approaches are urgently
needed. We used the laterally coupled 1D heat conduction model CryoGrid3
to simulate permafrost degradation affected by linear infrastructure. We
present a case study of a gravel road built on continuous permafrost (Dalton
highway, Alaska) and forced our model under historical and strong future
warming conditions (following the RCP8.5 scenario). As expected, the presence
of a gravel road in the model leads to higher net heat flux entering the
ground compared to a reference run without infrastructure and thus a higher
rate of thaw. Further, our results suggest that road failure is likely a
consequence of lateral destabilisation due to talik formation in the ground
beside the road rather than a direct consequence of a top-down thawing and
deepening of the active layer below the road centre. In line with previous
studies, we identify enhanced snow accumulation and ponding (both a
consequence of infrastructure presence) as key factors for increased soil
temperatures and road degradation. Using differing horizontal model
resolutions we show that it is possible to capture these key factors and their
impact on thawing dynamics with a low number of lateral model units,
underlining the potential of our model approach for use in pan-Arctic risk
assessments. Our results suggest a general two-phase behaviour of permafrost degradation:
an initial phase of slow and gradual thaw, followed by a strong increase in
thawing rates after the exceedance of a critical ground warming. The timing of
this transition and the magnitude of thaw rate acceleration differ strongly
between undisturbed tundra and infrastructure-affected permafrost ground. Our
model results suggest that current model-based approaches which do not
explicitly take into account infrastructure in their designs are likely to
strongly underestimate the timing of future Arctic infrastructure failure. By using a laterally coupled 1D model to simulate linear
infrastructure, we infer results in line with outcomes from more complex 2D
and 3D models, but our model's computational efficiency allows us to account
for long-term climate change impacts on infrastructure from permafrost
degradation. Our model simulations underline that it is crucial to consider
climate warming when planning and constructing infrastructure on permafrost as
a transition from a stable to a highly unstable state can well occur within
the service lifetime (about 30 years) of such a construction. Such a
transition can even be triggered in the coming decade by climate change for
infrastructure built on high northern latitude continuous permafrost that
displays cold and relatively stable conditions today.