HGS RESEARCH HIGHLIGHT – Simulating the recession dynamics of Arctic catchments in the context of a thawing permafrost
Sergeant, F., Therrien, R., Anctil, F., & Gatel, L. (2023). Simulating the recession dynamics of Arctic catchments in the context of a thawing permafrost. In Journal of Hydrology (Vol. 623, p. 129847). Elsevier BV. https://doi.org/10.1016/j.jhydrol.2023.129847
“HGS enables to simulate surface water and river flow with more realism. It is a crucial asset considering that river hydrograph is central in recession analysis. First, HGS allows to integrate surface with subsurface flow, which avoids the need to either neglect surface flow or create an ‘artificial’ boundary condition to account for its interactions with the subsurface. Then, while most previous model applications represent the river outlet as constant head or specified pressure, HGS offers larger panels of less-constraining boundary condtions for the river outlet, such as the critical depth boundary used here.”
CLICK HERE TO READ THE ARTICLE.
In a recent study, researchers have made significant strides in understanding how climate warming is altering the Arctic's hydrological dynamics.
The study - led by F. Sergeant and colleagues at the Université Laval - delves into the complex relationship between permafrost thaw and groundwater flow. Traditionally, Arctic hydrology has been conceptualized as a local system, confined by the frozen ground. However, as the climate warms, permafrost begins to thaw, transitioning this system into a more interconnected network of regional aquifers. This transformation is crucial, as it alters the fundamental dynamics of water movement and storage in the Arctic.
The team utilized HydroGeoSphere (HGS) to unravel the complex and dynamic hydrology Artic regions with receding permafrost. Their approach distinguished between the impacts of permafrost thawing in terms of its extent and thickness on local hydrology.
One of the study's key findings is the clear increase in vertical connectivity in subsurface flow paths, a result of river-talik development and valley incision. This finding challenges the previously held notion that the recession slope of an Arctic catchment hydrograph is linearly related to permafrost thawing depth. The study shows that this relationship is far more complex, influenced by factors such as the extent of permafrost, landscape topography, and aquifer properties.
Significantly, the research aligns with the dynamics observed in 336 real Arctic catchments, strengthening the validity of their conclusions. This alignment also highlights the limitations of the Brutsaert conceptual model, which fails to accurately relate recession constant to permafrost thaw depth under varying conditions. In conclusion, the study by Sergeant et al. not only advances our understanding of Arctic hydrology in the face of climate change but also paves the way for refining the recession analysis method. This method could potentially enable a more accurate determination of the hydrological signatures of Arctic rivers, directly relating them to permafrost thawing rates under varying environmental conditions. This research is a testament to the evolving nature of hydrological science and its critical role in understanding and adapting to the impacts of global climate change.
The study also perfectly demonstrates the powerful and varied toolkit available to HGS users. The researchers make full use of a number of advanced modules such as the built in pore-water freeze thaw module, hydraulic mixing cell approach for tracking water sources and time-varying material properties among many other features.
“The flexibility provided by HGS adaptable modules allows to bring more realism to our model. It could also be used to test other factors such vegetation or snow cover by incorporating the evaporation module accordingly. Besides, the hydraulic mixing cell approach incorporated in
HGS (Partington et al., 2011), which informs on the origin of the discharging water, could complement our understanding of the hydrological mechanisms involved”
Abstract:
In cold regions, climate warming is causing permafrost to thaw, which modifies the dynamics of groundwater flow from a local system, constrained by frozen ground, to a regional system of interconnected aquifers. Under the assumption presented in Brutsaert (2005), the recession slope of an arctic catchment hydrograph is linearly related to permafrost thawing depth. The recession analysis of arctic river flow may therefore reflect permafrost thawing dynamics. In areas where permafrost observations are rare, recession analysis appears as a valuable method to be exploited since there are extensive datasets of river-discharge for the Arctic, with an exceptionally large temporal and spatial coverage. Yet, it has been shown that the linear relationship between recession slope and permafrost thaw depth may be complicated by the extent of the permafrost, the landscape topography as well as the hydraulic properties of the aquifer. The integrated surface and subsurface hydrologic model Hydrogeosphere (HGS) is used here to account for hydrological complexifications and mechanisms involved when permafrost extent decreases and landscape hillslope increases. Previous modeling studies have already tested the impacts of these factors on the hydrological signature of arctic catchments. However, few have been able to (1) simulate permafrost extent, catchment hillslope and the resulting groundwater flowpaths in three dimensions, (2) distinguish the impact of permafrost thawing in extent from those of permafrost thawing in thickness and (3) represent the connection between surface and subsurface with a coupled approach. These assets allow to conclude that river-tàlik development and valley incision both clearly increase the vertical connectivity of the subsurface flowpaths as well as the non-linearity of the reservoir. The flexibility and the realism of HGS model allow to compare the modeling outputs with the dynamics of 336 real catchments from the Arctic. The comparison corroborates our results: below continuous, assumptions behind Brutsaert conceptual model are not verified and it is no longer possible to relate recession constant to permafrost thaw depth. Finally, this study gives the keys to start elaborating on the recession analysis method to be able to relate the hydrological signature of Arctic rivers to permafrost thawing rate in any type of permafrost extent and catchment topography.