My PhD work focuses on physical controls on water storage and flux on Arctic hillslopes. I'm going to start sharing some of this work on here in order to practice communicating this information simply, clearly, and concisely. Here it goes.
In many parts of the Arctic, mean annual temperatures are below freezing. Over time, this has caused permafrost, permanently frozen ground, to develop. In my study area in the foothills of the Brooks Range, permafrost is continuous over large spatial areas and extends below ground to several hundred meters depth. However, something changes every summer: a thin upper layer of the permafrost, called the "active layer" warms and thaws as air temperatures soar above freezing for a few months- usually from late May to mid-September. This brief time window allows plants and other organisms to flourish on and in the unfrozen soils. Water too is able to flow into and out of the subsurface, carrying with it the substances that it dissolves such as mineral salts that weather out of the glacial till that makes up the hills and valleys, as well as the nutrients that feed biotic productivity. As the active layer deepens over the summer, the amount of time that water spends in the ground and the depths and subsurface materials that it can reach grow as well. This is one seasonal component to how water storage and flux change in the Arctic.
Water enters Arctic landscapes through rain and snow and leaves through runoff, shallow subsurface flow, sublimation, evaporation, and transpiration by organisms. Unlike many places on Earth, hardly any water is able to penetrate deeply into the ground to become part of a long-lasting groundwater reservoir because the permafrost prevents it. The difference in precipitation phase is another seasonal difference in water storage and flux in the Arctic, although the change is causes is stochastic. Over winter, snow accumulates and is stored on the surface in snowpack. A small portion sublimates, but most of the stored snow is lost during spring snowmelt. This is a rapid event, where the snowpack becomes isothermal then melts away, usually within the span of a week or even a few days. Most of the water quickly flows in the stream network, causing the stream water discharge to increase dramatically too. This flood pulse is the largest in most years, but sometimes summer rainstorms can cause even greater flood events.
One of the datasets that I collect is the amount of water stored in the snowpack on the hillslopes of my study area at the beginning of my field seasons. Here's the procedure:
The amount of water stored in snowpack at the end of winter in 2013 was unusually large. For comparison, on average 12.9 cm of water were stored in snowpack in the spring each year in Upper Kuparuk River watershed in the mid-90s. From the 24 hillslope snowpits I dug, I measured an average of 23.6 cm of snow water equivalent. However, half the sampling locations I chose target features called water tracks that form in areas of convergent topography that drain the hillslopes. The other half are from non-water track locations. Comparing the two, I found that the water stored in the water track snowpack was significantly higher, likely because they form topographic lows and contain emergent shrubby vegetation that trap snow when the wind redistributes it over the winter.
In many parts of the Arctic, mean annual temperatures are below freezing. Over time, this has caused permafrost, permanently frozen ground, to develop. In my study area in the foothills of the Brooks Range, permafrost is continuous over large spatial areas and extends below ground to several hundred meters depth. However, something changes every summer: a thin upper layer of the permafrost, called the "active layer" warms and thaws as air temperatures soar above freezing for a few months- usually from late May to mid-September. This brief time window allows plants and other organisms to flourish on and in the unfrozen soils. Water too is able to flow into and out of the subsurface, carrying with it the substances that it dissolves such as mineral salts that weather out of the glacial till that makes up the hills and valleys, as well as the nutrients that feed biotic productivity. As the active layer deepens over the summer, the amount of time that water spends in the ground and the depths and subsurface materials that it can reach grow as well. This is one seasonal component to how water storage and flux change in the Arctic.
Water enters Arctic landscapes through rain and snow and leaves through runoff, shallow subsurface flow, sublimation, evaporation, and transpiration by organisms. Unlike many places on Earth, hardly any water is able to penetrate deeply into the ground to become part of a long-lasting groundwater reservoir because the permafrost prevents it. The difference in precipitation phase is another seasonal difference in water storage and flux in the Arctic, although the change is causes is stochastic. Over winter, snow accumulates and is stored on the surface in snowpack. A small portion sublimates, but most of the stored snow is lost during spring snowmelt. This is a rapid event, where the snowpack becomes isothermal then melts away, usually within the span of a week or even a few days. Most of the water quickly flows in the stream network, causing the stream water discharge to increase dramatically too. This flood pulse is the largest in most years, but sometimes summer rainstorms can cause even greater flood events.
One of the datasets that I collect is the amount of water stored in the snowpack on the hillslopes of my study area at the beginning of my field seasons. Here's the procedure:
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| Dig a snowpit to the base of the snowpack. |
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| Describe the snow profile and identify layers in the snow for sampling. |
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| Take samples of a known volume and weigh in the lab to determine density. |
The amount of water stored in snowpack at the end of winter in 2013 was unusually large. For comparison, on average 12.9 cm of water were stored in snowpack in the spring each year in Upper Kuparuk River watershed in the mid-90s. From the 24 hillslope snowpits I dug, I measured an average of 23.6 cm of snow water equivalent. However, half the sampling locations I chose target features called water tracks that form in areas of convergent topography that drain the hillslopes. The other half are from non-water track locations. Comparing the two, I found that the water stored in the water track snowpack was significantly higher, likely because they form topographic lows and contain emergent shrubby vegetation that trap snow when the wind redistributes it over the winter.
Overall, the average snow water equivalent in the water track locations was ~28 cm, while the hillslope sites contained ~18 cm. This is still significantly greater than other years and makes for an exciting peek into what could happen in the future, when climate models predict that over winter Arctic snowfall will increase. I would also predict that ground temperatures, active layer thaw, and potentially water storage in the water track may be greater than the surrounding hillslope. Next, I need to investigate the timing of snowpack formation and melt at my different field sites. Since snow shields the ground from harsh winter air temperatures, both the timing and magnitude of snowpack are important factors in determining summer active layer conditions.
