Characterizing Runoff Regimes in Subarctic Wetland-Dominated Landscapes: Application to the Hudson Bay Lowlands, Canada

In the past decades, climate warming has led to widespread permafrost thaw and subsequent land cover change in subarctic wetland-dominated landscapes found in the discontinuous permafrost zone (<90% areal extent). Long-term hydrometric records and extensive field studies in northwestern Canada have demonstrated measurable increases in runoff as a consequence of permafrost-thaw-induced land cover change. Land cover changes are largely attributed to the loss of boreal forest area that is dependent on elevated and dry peat plateaus. As permafrost thaws, the peat plateaus amalgamate with surrounding bogs and fens. This has led to both transient and permanent increases to runoff via peatland drainage and increased hydrological connectivity, respectively. However, it remains unknown whether these land cover and runoff changes are a regional occurrence or applicable to all circumpolar regions.

The Hudson Bay Lowlands in central Canadian are the world's third largest contiguous wetland complex (225,000 km²), for which many areas are underlain with permafrost. Unfortunately, the remoteness of the Hudson Bay Lowlands has made it difficult collect long-term hydrometric records and engage in intensive field studies.

In this study we attempt to better understand how permafrost-thaw-induced land cover change is affecting the Hudson Bay Lowlands. We suggest that by characterizing runoff regimes across 40 pan-subarctic wetland-dominated catchments where hydrometric records are available and land cover information is discernible using remote sensing classification techniques. We can use runoff regimes as a conceptual framework to better understand land cover controls of runoff in the Hudson Bay Lowlands where land cover information is discernible, but sparse long-term hydrometric records exist. For this study we characterize runoff regimes using runoff ratio and response time trends which reflect the sources and timing of runoff. Those trends are then sorted by land cover type prevalence to designate our proposed runoff regimes. We discuss insights and challenges to understanding the impacts of permafrost thaw on runoff in the ungauged catchments of the Hudson Bay Lowlands.