Snowpack Monitoring: The First Three Years

HIA’s snowpack monitoring project has just completed a third year in the field! Our results show that while calculating a precise amount of snow in Gartina Basin is complicated, higher elevations tend to accumulate deeper and longer lasting snow. We also look forward to deploying our new weather stations during the upcoming field season!

Background

2018 saw the Alaskan Southeast experiencing the driest and second hottest year in the historical record. These results align with climate models predicting a warmer future—the average temperature in the majority of the Southeast is predicted to rise between 1.6- and 2.3-degrees Fahrenheit by 2050. The average precipitation in the region will increase some two to five percent, but up to 85 percent of the area will no longer receive snow in the winter by the end of the century. Since all the members of an ecosystem are tied together, the changes in climate will impact not just the plant life of the region, but also the humans and animals that depend on these resources.

Historical trend for the dates of snow coverage in Alaska. While individual years show variation, the overall effect is a shorter duration of snow that arrives later and melts earlier. While we do not yet have a long enough baseline to do this sort of analysis for Hoonah, and this graph includes state-wide data and not just those from the Southeast, we can assume the general effect locally will be similar. Taken from Rick Thoman, Alaska Center for Climate and Policy.

Changing precipitation amounts and types will have a variety of ecological impacts on Hoonah and Southeast Alaska at large. These include, but are not limited to:

  • An increase of rain on snow events, which result in a frozen crust on top of vegetation that herbivores cannot break through. This leads to mass starvation and die-off events in the deer population.
  • Rising stream temperatures, which directly effect salmon lifecycles and populations, with earlier spawning and increased flow rates damaging eggs and raising mortality rates in both juvenile and adult fish.
  • Decreased subsistence resources, which will have drastic impacts on residents ability to put food on the table. 94 percent of households reported consuming deer and 100 percent consumed salmon during the 2020 food assessment.
  • Decline in yellow cedar populations, including extensive loss already documented on the western edge of Chichagof Island, as the trees need snow to insulate their roots during the winter.
  • Decreased hydroelectric energy production from IPEC; Hoonah saved $34,434 by using the hydro plant as opposed to just burning diesel in April 2022.
  • Decrease in the municipal water supply, as Hoonah gets sits water from Gartina Creek at the base of Ear Mountain

Given the number and range of the impacts of reduced snowpack, it is critical to have accurate, local data about current conditions and how they may change in the future.

To address these concerns, in 2020, the City of Hoonah worked with HIA to establish a snow pack monitoring network. The City provided funding for supplies and labor costs for the construction of the network. We now have two years of data to give us insight into snowpack conditions in Gartina Basin and will be collecting a third season of data in the summer of 2022. HIA has now secured funding to improve on the technology and will be deploying upgraded stations during the 2022 field season. This report is intended to summarize the results to date, present the data to date, and investigate how these data may be of use to the City and community for climate preparedness moving forward.

Methodology

The current snowpack monitoring network is comprised of fifteen poles on four transects, deployed at a variety of elevations and aspects throughout Gartina Basin. The elevations range from approximately 240 meters (790 feet) above sea level to just shy of 500 meters (1620 feet), while the aspects of the terrain range from 28 to 330 degrees relative to north. The poles on transect one are located primarily in muskegs, while the other transects are in woodland terrain. All sites were chosen to be relatively free of canopy tree cover that would interfere with snowfall and solar radiation.

This is an example of the snow pole stations that are currently in operation. The middle two temperature loggers are clearly visible on the pole, while the bottom-most is out of frame and the top one is hidden under the white radiation shield. More recently deployed poles are based on metal, not wooden, fence posts, as they are more likely to survive the bears and inclement weather.

Each pole is approximately 2 meters tall and contains 4 temperature loggers, located at 0.25 meters, 0.5 meters, 1 meter and approximately 1.4 meters off the ground. The top sensor is covered with a reflective solar radiation shield to minimize warming by the sun and provide more accurate air temperature readings. We assume that each logger is buried in snow when the temperature is between 30- and 33-degrees Fahrenheit and the variance (a measure of daily temperature variation) is less than one. Of the 60 deployed sensors, five were damaged by bears and four were not read due to snow coverage when the data was retrieved, resulting in a 91 percent success rate in data retrieval where attempted.

For more information about our data processing and the details of the network construction, check out our code on GitHub!

Results

Example temperature profile for a single pole. The temperature flatlining means the snow has reached that depth. The spring thaw can be seen progressively occurring in May 2021 as the top sensors are uncovered first and the lowest sensor remains buried until some two weeks after the melting begins. The downward spike in the temperatures in late January was due to higher temperatures immediately preceding those dates that melted the snow, resulting in a lack of insulation around the sensors that caused their temperatures to fall.

Sensor coverage as a function of time for pole 14, indicating light to moderate snow coverage for the first part of the winter followed by snow depths in excess of 1.4 meters after the new year. The inability to precisely ascertain snow pack levels and the relatively low maximum depth that we can measure highlights the need for our more the advanced monitoring stations.

Many of our key results exactly follow what intuition about snow would imply; higher elevations have deeper, longer lasting snow than lower locations, the first heavy snow is found in late November through mid-December and there is snow present at many locations through the end of May. Several poles failed to accumulate at least a meter of snow, and all those poles were found at or below 390 meters (1300 feet). Not all the snow behavior is dependent on elevation though, otherwise pole 11 would not have thawed prior to pole 10 and the frequency of light thawing events would decrease with increased elevation. We also found no differences in the snow accumulation on muskeg versus woodland terrain despite the on-going decomposition in the former, nor on the east versus west halves of the basin despite the difference in solar radiation on the surface, though this may have been obscured by the course resolution of our depth measurements. Finally, several poles were warmer at the base than the top, which is the sort of behavior that triggers avalanches and other dangerous conditions. While there are still unanswered questions, it is still clear that our network has shown the complexity of monitoring snowpack and is a solid first stage for future work.

Future Developments

The depth of snow pack depends on many factors, including, elevation, wind speed and direction, solar radiation, aspect and precipitation. Given the number of factors, it can be hard to understand what’s happening in the whole basin just based on a few poles in a small area. Furthermore, our current monitoring network fails to provide real depth information; while we can accurately determine if each sensor is buried and thus provide a lower limit on the snow depth, we cannot get measurements between sensor heights or above the maximum height of the pole, which are not uncommon in this area. For example, our current methodology cannot tell the difference between snow depths of 0.51 and 0.99 meters, as they would both have the same temperature profile, and we have no way of gauging the snow depth once it passes 1.4 meters. Our current methods also fail to capture the density of the snow and thus cannot be easily converted into an exact amount of water in the basin.

The current limitations in our data and the information they can provide highlight the need for improved sensors to monitor the level of snowpack near Hoonah. To that end, the Hoonah Indian Association’s environmental office is currently designing a network of upgraded monitoring stations that will be installed at the mouth of the Gartina basin during the next two field seasons. The stations will use SONAR to detect the snow depth with sub-centimeter precision and will be able to measure depths up to fifteen feet. The table shows the instrumentation we plan on installing and the motivation behind each of the measurements we’ll be taking.

As the well-being of Hoonah is tied closely to the water supply, the ability to monitor our resources will become increasingly important as the climate, rain and snow change. Our work will not just serve just our community, as we’ll also be able to report our values to the NASA-led Community Snow Observations network, a program that collates locally gathered data to look for regional and national trends in snow pack to track changes through time.

While site selection is on-going for the new sensors, we’re prioritizing a few key factors

  1. SONAR sensors must be installed over relatively flat ground in order to get accurate snow depth measurements.
  2. We need minimal tree cover, as overhanging branches will impede snowpack development, while also avoiding exposed slopes where the wind will reduce snow accumulation.
  3. A range in elevations will provide the largest base-line for snow conditions, but we must select elevations that hold snow throughout the spring.
  4. At least one station will hopefully be in muskeg, since that terrain holds more water throughout the year and provides a larger fraction of the municipal water supply than woodland soil does.
  5. Accessibility from the road system will facilitate easier and thus more frequent measurements of the Snow Water Equivalency.

The fact that the climate is changing should come as no surprise—the evidence is abundant in our own backyards. Developing a historical record and maintaining real-time data access to the status of our natural resources will be increasingly important as we adapt and prepare for the new normal. Climate change may make our weather less predictable, but the new snow stations will help us provide the most accurate forecasts and conservation efforts possible, while the existing data from our current network will help contextualize those results.

1 Comment

  1. What an interesting program! Very good data! Gunal’cheech!
    Just a thought. Tenakee Inlet Conservation Council has been gathering data on their watershed levels for the past few years. Seems like a good opportunity to contact them and share information efforts.

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