The hydrologic impacts of a subarctic landscape in transition

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Temperatures in the Arctic and subarctic are rising faster than the global average. Predictions suggest that by 2050, near-surface permafrost (permanently frozen soils) will have decreased by about 35% compared to current conditions. One documented consequence of permafrost degradation is a transformation of the hydrological cycle from a surface-water to a groundwater-dominated system-a shift which would significantly modify the terrestrial (not atmospheric) portion of the water cycle. The transition toward groundwater-dominated hydrological systems has the potential to greatly impact the water supplies of communities in northern Canada. Currently, these communities primarily rely on surface water bodies, such as rivers and lakes, for their water supplies. While these sources of water can be abundant, the water quality and volume is often variable, as they are easily contaminated and may freeze or dry up during the winter. In contrast, groundwater is generally less vulnerable to contamination and usually requires only minimal treatment. Yet because groundwater is currently stored as ground ice in permafrost, access to groundwater has historically been limited for most northern communities. While continued permafrost degradation is increasing the availability of groundwater in these areas, how the reactivation of these groundwater flow systems will impact the water cycle (and, by extension, the water supplies of northern communities) is still not well understood. Understanding the hydrological implications of continued permafrost degradation is further complicated by the extensive geomorphological and ecological transformations that often occur simultaneously with permafrost thaw. A prominent example of these linked phenomena is the impact that the greening of the tundra due to the expansion of shrubs has on groundwater recharge. The expansion of shrub populations strongly influences snow distribution; as taller vegetation traps more snow than bare land. Since the spring snowmelt is the main groundwater recharge event in subarctic environments, changes in vegetation cover are likely to alter the spatial distribution of groundwater recharge. Yet despite recent work, our ability to predict how a changing landscape will influence local hydrology is limited, due to both the complexity of the northern water cycle, as well as challenges associated with accessing the territory. This research program aims to improve our understanding of the hydrological cycle in the subarctic, in order to anticipate how climate warming and landscape evolution will impact the availability of groundwater and surface water. The research will rely on field observations in a subarctic watershed as well as advanced computer simulations. The results of this research will contribute to the sound and sustainable management of freshwater resources in northern environments, and may help northern Canadian communities to gain access to safer, more reliable drinking water supplies.