Impact of heat advection on the thermal regime of roads built on permafrost

Abstract

In northern regions, transportation infrastructure can experience severe structural damages due to permafrost degradation. Water infiltration and subsurface water flow under an embankment affect the energy balance of roadways and underlying permafrost. However, the quantification of the processes controlling these changes and a detailed investigation of their thermal impacts remain largely unknown due to a lack of available long‐term embankment temperature data in permafrost regions. Here, we report observations of heat advection linked to surface water infiltration and subsurface flow based on a 9‐year (from 2009 to 2017) thermal monitoring at an experimental road test site built on ice‐rich permafrost conditions in southwestern Yukon, Canada. Our results show that snowmelt water infiltration in the spring rapidly increases temperature in the upper portion of the embankment. The earlier disappearance of snow deposited at the embankment slope increases the thawing period and the temperature gradient in the embankment compared with the natural ground. Infiltrated summer rainfall water lowered the near‐surface temperatures and subsequently warmed embankment fill materials down to 3.6‐m depth. Heat advection caused by the flow of subsurface water produced warming rates at depth in the embankment subgrade up to two orders of magnitude faster than by atmospheric warming (heat conduction). Subsurface water flow promoted permafrost thawing under the road embankment and led to an increase in active layer thickness. We conclude that the thermal stability of roadways along the Alaska Highway corridor is not maintainable in situations where water is flowing under the infrastructure unless mitigation techniques are used. Severe structural damages to the highway embankment are expected to occur in the next decade.

Seasonal evolution of active layer thaw depth and hillslope‐stream connectivity in a permafrost watershed

“…Thaw depths may vary substantially even over short distances (1 to 10 m) emphasizing the importance of localized processes on active layer thaw (Gao et al, 2016). In particular, subsurface flows or wetness conditions can influence the local variation in thaw by enhancing the transfer of thermal energy via heat conduction and convection (Chen et al, 2019;de Grandpré et al, 2012;Hayashi et al, 2007;Quinton et al, 2005). In turn, spatially variable thaw patterns can influence surface soil moisture distribution (Guan et al, 2010;Williams et al, 2013;Wright et al, 2009).…”

The role of vadose zone physics in the ecohydrological response of a Tibetan meadow to freeze–thaw cycles

“…From the perspective of energy fluxes, the convective heat flux and explicit frozen soil physics are taken into account in the CPLD model, while they are not considered in the two unCPLD models. The difference among models in simulating the liquid-water-fluxinduced convective heat flux is mostly relevant to the freezing or thawing process (Kane et al, 2001;Boike et al, 2008;Sjöberg et al, 2016;Chen et al, 2020;Yu et al, 2020). As has been observed, a certain amount of liquid water/vapor flux moves toward the freezing front, and this effect is different between unCPLD-FT and CPLD, while it is absent in unCPLD (Fig.…”

“…The energy balance closure problem, usually identified because the sum of latent (LE) and sensible (H ) heat fluxes is less than the available energy (Rn − G 0 ), is quite common in eddy covariance measurements (Su, 2002;Wilson et al, 2002;Leuning et al, 2012). The energy imbalance of EC measurements is particularly significant at sites over the Tibetan Plateau (Tanaka et al, 2003;Yang et al, 2004;Chen et al, 2013;Zheng et al, 2014). Figure 10 presents the energy imbalance of hourly LE and H by the eddy covariance measurements, observed Rn by the four-component radiation measurements, and the estimated ground heat flux (G 0 ) by the CPLD model.…”

Invited Perspective: What Lies Beneath a Changing Arctic?

“…As permafrost thaws in ice-rich regions, the ground subsides unevenly leading to thermokarst features and unstable slopes, both of which are destructive to surface structures and incur local and regional costs to society (Figure 1; Hjort et al, 2018). Although it is generally overlooked, the flow of groundwater beneath structures built on permafrost can increase thaw and enhance subsidence rates (Chen et al, 2019). In some cases, erosion and water ponding around subsiding structures requires costly engineering solutions to reroute excess water.…”