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On the seasonal hydrological and thermal regimes of Arctic hillslopes: Field and modeling investigations in the context of climate change.
Department: Geology
Specimen Elements
Unknown to Unknown
Caitlin Rushlow
Idaho State University
City: Pocatello
In upland Arctic watersheds, features called water tracks commonly drain the precipitation received by hillslopes through the shallow soils of the seasonally thawed active layer to downslope aquatic ecosystems. Little is known about the seasonal extent and controls on this hydrologic connection, and how it may be affected by the rapid changes occurring in the regional climate. I measured the runoff generated by water tracks in response to rainfall during the thaw season and found that the response was often delayed relative to the stream network due to storage within the hillslope watershed. Runoff was proportional to rainfall once it exceeded the water storage capacity near the water track outlet. Runoff generation thresholds varied by site, emphasizing the role of spatially distributed water storage and exceedance patterns in controlling the emergent response at each water track. While it is generally assumed that hydrological and ecological processes are relatively quiescent in the cold season, I found that the active layer of water tracks remained thawed or only partially frozen for months longer than the surrounding hillslope. Water tracks also thawed later than hillslopes in the spring, delaying interaction between soils and spring snowmelt. The persistence of conditions favorable to biological activity and hydrologic transport suggest that water tracks may function as hot spots of greenhouse gas emissions in the cold season. Multiple linear regression results showed that most of the variation in active layer thermal conditions was explained by air temperature, feature, and snow depth. I used numerical models to further explore how those factors affect the thermal regime of the hillslope and water track active layer. I found that under the current climate, locations with deep snow can form taliks in warmer years, while in colder years, locations with shallow snow remain frozen for the majority of theyear. Further, groundwater flow redistributes heat, moderating active layer thermal regime in areas of aggregating flow, such as water tracks. The results of this study, together with the broad spatial extent of water tracks in permafrost watersheds, suggest that water tracks may play an underappreciated role in modulating the convolved hydrologic, geomorphic, and ecological responses of Arctic watersheds to climate change.

On the seasonal hydrological and thermal regimes of Arctic hillslopes: Field and modeling investigations in the context of climate change.

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