Permafrost degradation as a control on hydrogeological regime shifts in a warming climate

Abstract

[1] Using numerical models, we evaluate hydrogeological regime changes in high-latitude river basins under conditions of ground surface warming. These models describe transient heat-and fluid flow coupled to the hydrogeological impacts of phase-changes from ice to liquid water. We consider an idealized unconsolidated sedimentary aquifer system in which groundwater flow is driven by topography, representing a series of small drainage basins in riverine terrain of relatively subdued topography. Various temporal and spatial surface temperature conditions are considered to control the initial permafrost distributions for the simulations. The simulated rates of increase in groundwater contribution to streamflow during and after permafrost thaw, are in the order of magnitude comparable to hydrogeological regime changes over the past decades as reported for several (sub-)Arctic rivers. The simulations further show that two distinct features of the subsurface response control the temporal evolution of base flow increase: (1) shifts in aquifer permeability architecture during permafrost degradation and (2) uptake of water into aquifer storage when sub-permafrost hydraulic heads rise. Model analysis shows that the latter process delays base flow increase by several decades to centuries. In order to evaluate the relative importance of both processes in natural systems, the current hydraulic regime of sub-permafrost aquifer systems as well as patterns of permafrost heterogeneity, taliks and their hydraulic connectivity are insufficiently known.

Estimating interaction between surface water and groundwater in a permafrost region using heat tracing methods

“…Many groundwater modeling studies in permafrost regions have reported on the subsurface fluxes, including soil drainage and recharge, and suprapermafrost flow. These studies have also shown that SW-GW exchanges can increase as the 10 active layer thickening, with water uptake into suprapermafrost aquifer occurring when subpermafrost hydraulic heads rise (Bense et al, 2009(Bense et al, , 2012Evans et al, 2015;Ge et al, 2011). Although our observations did not demonstrate the impact of changes to the permafrost table, our results show increasing interactions between SW-GW with active layer thawing.…”

“…Significant hydrological changes in permafrost regions have received worldwide attention because water resources and ecosystems are particularly vulnerable to climate change (Bense et al, 2012;Woo, 2012;Walvoord and Kurylyk, 2016). Due to its hydrogeological function as an aquitard, permafrost impacts the movement, storage, and exchange of surface water (SW) and 5 groundwater (GW).…”

“…Although explanations of the linkage between permafrost thaw and hydrological processes abound, the logistical challenges of measuring and monitoring subsurface water fluxes and storage in permafrost regions limits the predictions of how future climate change may influence hydrological conditions in these regions (Walvoord et al, 2012;Walvoord and Kurylyk, 2016). Furthermore, existing modeling studies of increases in baseflow and sub-permafrost flow are based on hypothetical scenarios (Ge et al, 2011;Bense et al, 2012). 20 Heat tracing methods have been used to identify and quantify reach-specific SW-GW interactions in humid environments (Constantz et al, 2013;Irvine et al, 2017).…”

Strong degradation of palsas and peat plateaus in northern Norway during the last 60 years

“…In river hydrology, several studies suggest permafrost thawing as one contributing reason to a widely observed increase in river base flow (e.g. Bense et al, 2012;St Jacques and Sauchyn, 2009;Walvoord and Striegl, 2007), which has also been observed in areas of Fennoscandia where palsa mires are known to exist (Sjöberg et al, 2013;Wilson et al, 2010).…”

Increasing Winter Baseflow in Response to Permafrost Thaw and Precipitation Regime Shifts in Northeastern China

“…Some modeling studies have also demonstrated a phase shift between base flow response and permafrost thaw, but the results vary depending on the hydrogeologic system in question. For instance, Bense et al [75] found that the process of uptake of water into aquifer storage following an increase in sub-permafrost hydraulic heads delays base flow increases by decades to centuries. However, the modeling results of Ge et al [26] indicated changes to the maximum shallow supra-permafrost groundwater discharge lagged the maximum subsurface temperature by less than one year.…”