The thermal response of permafrost to coastal floodplain flooding

Abstract

Flooding of low-lying Arctic regions has the potential to warm and thaw permafrost by changing the surface reflectance of solar insolation, increasing subsurface soil moisture, and increasing soil thermal conductivity. However, the impact of flooding on permafrost in the continuous permafrost environment remains poorly understood. To address this knowledge gap, we used a combination of available flooding data on the Ikpikpuk delta and a numerical model to simulate the hydro-thermal processes under coastal floodplain flooding. We first constructed the three most common flood events based on water level data on the Ikpikpuk: snowmelt floods in the late spring and early summer, middle and late summer floods, and floods throughout the whole spring and summer. Then the impact of these flooding events on the permafrost was simulated for one-dimensional permafrost columns using the Advanced Terrestrial Simulator (ATSv1.0), a fully coupled permafrost-hydrology and thermal dynamic model. Our results show that coastal floods have an important impact on coastal permafrost dynamics with a cooling effect on the surficial soil and a warming effect on the deeper soil. Cumulative flooding events over several years can cause continuous warming of the deep subsurface but cool down the surficial layer. Flood timing is a primary control of the vertical extent of the permafrost thaw and the active layer deepening.

Disparate permafrost terrain changes after a large flood observed from space

“…Although limited data quality and spatial resolution preclude precise estimates of the spatial extent of quasi‐instantaneous ice wedge degradation, our results (Figures 6 and S1) and prior studies 25,39 suggest only a small fraction of the study area was affected. The limited extent was plausibly favored by cold water temperatures of , the brief period of inundation, and low relief 12 . These factors may also explain the subdued subseasonal legacy in the observed 35‐cm soil temperature at the CALM site (Figure 11).…”

“…The limited extent was plausibly favored by cold water temperatures of $ 1 ∘ C, the brief period of inundation, and low relief. 12 These factors may also explain the subdued subseasonal legacy in the observed 35-cm soil temperature at the CALM site (Figure 11).…”

“…[3][4][5] Ice-rich banks can retreat by $10 m yr À1 due to thermal erosion. [6][7][8][9][10][11] Floodplains are also prone to permafrost thaw following enhanced energy transfer into the soils during 12,13 and after a flood through, for example, disruptions to the organic matter. [14][15][16] Equally, however, river floods are essential to floodplain aggradation.…”

“…1,18,21 The inherent variability of fluvial landscape dynamics is a major challenge for observational and predictive frameworks. 15,22 The variability is not restricted to differences between regions or flood events, 6,12,19 as the drivers, controls, and thus consequences are heterogeneous even for a single flood event. 16,23 Drivers such as shear stress, water temperature, and sediment deposition vary within the flood perimeter.…”

A Model for Thaw and Erosion of Permafrost Riverbanks

“…Developing a numerical model for this process requires tracking two moving boundaries: the permafrost thaw front and the eroding riverbank. Thus, modeling the thawed layer in permafrost riverbanks poses a distinct challenge that is not fully addressed by models focused on coastal erosion (e.g., Barnhart et al, 2014;Kobayashi & Aktan, 1986), river flooding (Zhang et al, 2023;Zheng et al, 2019), or talik development (Ohara et al, 2022;Roux et al, 2017). Likewise, Douglas, Miller, et al (2023) and Douglas, Dunne, and Lamb (2023) modeled permafrost riverbank erosion for the thawand entrainment-limited end members, but the model is incomplete because they did not dynamically track the pore-ice front nor the thawed-layer development.…”