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Abstract The thawing of permafrost in the Arctic has led to an increase in coastal land loss, flooding, and ground subsidence, seriously threatening civil infrastructure and coastal communities. However, a lack of tools for synthetic hazard assessment of the Arctic coast has hindered effective response measures. We developed a holistic framework, the Arctic Coastal Hazard Index (ACHI), to assess the vulnerability of Arctic coasts to permafrost thawing, coastal erosion, and coastal flooding. We quantified the coastal permafrost thaw potential (PTP) through regional assessment of thaw subsidence using ground settlement index. The calculations of the ground settlement index involve utilizing projections of permafrost conditions, including future regional mean annual ground temperature, active layer thickness, and talik thickness. The predicted thaw subsidence was validated through a comparison with observed long-term subsidence data. The ACHI incorporates the PTP into seven physical and ecological variables for coastal hazard assessment: shoreline type, habitat, relief, wind exposure, wave exposure, surge potential, and sea-level rise. The coastal hazard assessment was conducted for each 1 km²coastline of North Slope Borough, Alaska in the 2060s under the Representative Concentration Pathway 4.5 and 8.5 forcing scenarios. The areas that are prone to coastal hazards were identified by mapping the distribution pattern of the ACHI. The calculated coastal hazards potential was subjected to validation by comparing it with the observed and historical long-term coastal erosion mean rates. This framework for Arctic coastal assessment may assist policy and decision-making for adaptation, mitigation strategies, and civil infrastructure planning. 

This paper presents the results of a community survey that was designed to better understand the effects of permafrost degradation and coastal erosion on civil infrastructure. Observations were collected from residents in four Arctic coastal communities: Point Lay, Wainwright, Utqiaġvik, and Kaktovik. All four communities are underlain by continuous ice-rich permafrost with varying degrees of degradation and coastal erosion. The types, locations, and periods of observed permafrost thaw and coastal erosion were elicited. Survey participants also reported the types of civil infrastructure being affected by permafrost degradation and coastal erosion and any damage to residential buildings. Most survey participants reported that coastal erosion has been occurring for a longer period than permafrost thaw. Surface water ponding, ground surface collapse, and differential ground settlement are the three types of changes in ground surface manifested by permafrost degradation that are most frequently reported by the participants, while houses are reported as the most affected type of infrastructure in the Arctic coastal communities. Wall cracking and house tilting are the most commonly reported types of residential building damage. The effects of permafrost degradation and coastal erosion on civil infrastructure vary between communities. Locations of observed permafrost degradation and coastal erosion collected from all survey participants in each community were stacked using heatmap data visualization. The heatmaps constructed using the community survey data are reasonably consistent with modeled data synthesized from the scientific literature. This study shows a useful approach to coproduce knowledge with Arctic residents to identify locations of permafrost thaw and coastal erosion at higher spatial resolution as well as the types of infrastructure damage of most concern to Arctic residents. 

Abstract. Infrastructure built on perennially frozen ice-richground relies heavily on thermally stable subsurface conditions. Climate-warming-induced deepening of ground thaw puts such infrastructure at risk offailure. For better assessing the risk of large-scale future damage to Arcticinfrastructure, improved strategies for model-based approaches are urgentlyneeded. We used the laterally coupled 1D heat conduction model CryoGrid3to simulate permafrost degradation affected by linear infrastructure. Wepresent a case study of a gravel road built on continuous permafrost (Daltonhighway, Alaska) and forced our model under historical and strong futurewarming conditions (following the RCP8.5 scenario). As expected, the presenceof a gravel road in the model leads to higher net heat flux entering theground compared to a reference run without infrastructure and thus a higherrate of thaw. Further, our results suggest that road failure is likely aconsequence of lateral destabilisation due to talik formation in the groundbeside the road rather than a direct consequence of a top-down thawing anddeepening of the active layer below the road centre. In line with previousstudies, we identify enhanced snow accumulation and ponding (both aconsequence of infrastructure presence) as key factors for increased soiltemperatures and road degradation. Using differing horizontal modelresolutions we show that it is possible to capture these key factors and theirimpact on thawing dynamics with a low number of lateral model units,underlining the potential of our model approach for use in pan-Arctic riskassessments. Our results suggest a general two-phase behaviour of permafrost degradation:an initial phase of slow and gradual thaw, followed by a strong increase inthawing rates after the exceedance of a critical ground warming. The timing ofthis transition and the magnitude of thaw rate acceleration differ stronglybetween undisturbed tundra and infrastructure-affected permafrost ground. Ourmodel results suggest that current model-based approaches which do notexplicitly take into account infrastructure in their designs are likely tostrongly underestimate the timing of future Arctic infrastructure failure. By using a laterally coupled 1D model to simulate linearinfrastructure, we infer results in line with outcomes from more complex 2Dand 3D models, but our model's computational efficiency allows us to accountfor long-term climate change impacts on infrastructure from permafrostdegradation. Our model simulations underline that it is crucial to considerclimate warming when planning and constructing infrastructure on permafrost asa transition from a stable to a highly unstable state can well occur withinthe service lifetime (about 30 years) of such a construction. Such atransition can even be triggered in the coming decade by climate change forinfrastructure built on high northern latitude continuous permafrost thatdisplays cold and relatively stable conditions today.