Abstract
AbstractFire frequency and severity are increasing in high‐latitude regions, but the degree to which groundwater flow impacts the response of permafrost to fire remains poorly understood. Here we use the Anaktuvuk River Fire (Alaska, USA) as an example for simulating groundwater‐permafrost interactions following fire. We identify key thermal and hydrologic parameters controlling permafrost response to fire both with and without groundwater flow, and separate the relative influence of changes to the water and energy balances on active layer thickness. Our results show that mineral soil porosity, which influences the bulk subsurface thermal conductivity, is a key parameter controlling active layer response to fire in both the absence and presence of groundwater flow. However, including groundwater flow in models increases the perceived importance of subsurface hydrologic properties, such as the soil permeability, and decreases the perceived importance of subsurface thermal properties, such as the thermal conductivity of soil solids. Furthermore, we demonstrate that changes to the energy balance (increased soil temperature) drive increased active layer thickness following fire, while changes to the water balance (decreased groundwater recharge) lead to reduced landscape‐scale variability in active layer thickness and groundwater discharge to surface water features such as streams. These results indicate that explicit consideration of groundwater flow is critical to understanding how permafrost environments respond to fire.
Highlights
Fire frequency and severity in the Arctic are expected to increase in the future and can have large-scale and long-lasting effects on hydrological and biogeochemical cycling (Flannigan et al, 2005; Hu et al, 2015)
Soil thermal conductivity has a secondary effect on mean annual active layer thickness in the 1-D simulations, with the relative importance of organic and mineral soil depending on burn severity (Figure 3, top row)
Including groundwater flow increases the relative importance of hydraulic properties and decreases the relative importance of thermal properties, indicating that subsurface heat transport by advection is of greater importance than heat transport by conduction (Figures 3 and 4)
Summary
Fire frequency and severity in the Arctic are expected to increase in the future and can have large-scale and long-lasting effects on hydrological and biogeochemical cycling (Flannigan et al, 2005; Hu et al, 2015). Past modeling efforts studying postfire active layer thickness have primarily concluded that soil thermal properties are the most important control on permafrost response to fire (Jiang et al, 2012; Jiang, Rastetter, et al, 2015; Yi et al, 2009) These studies neglected the potential impacts of lateral groundwater flow on permafrost thaw by using onedimensional models (Brown et al, 2015; Jiang, Rastetter, et al, 2015; Treat et al, 2013; Yi et al, 2009; Zhang et al, 2003, 2015; Zhuang et al, 2002)
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