Integrated Regional Analyses of Snowmelt Processes Across Northern Alaska

1. Integrated Regional Analyses of Snowmelt Processes Across Northern Alaska We had an excellent opportunity this spring to conduct a simple regional-scale experiment in arctic hydrology and remote sensing. The "experiment" consisted of obtaining detailed ground-based observations of snow conditions during the melt from a wide variety of locations and types of snow cover, and comparing these observations to remote sensing products collected during the same period. The project was possible because there were already a number of groups who were monitoring snow melt in Alaska this past spring, and several of these groups committed to coordinating their measurements. Snowmelt in the Arctic is hydrologically important and a dramatic time of year; the land surface can change from fully snow-covered to snow-free in one week, and in some catchments, as much as 80% of the annual run-off is generated. It is also the time when the snow cover undergoes its greatest changes in properties, resulting in the most dramatic changes in remote sensing signals. Temporal and spatial patterns developed during the snowmelt are determined by the weather and the stratigraphic character of the snow. Different climate classes of snow, such as taiga and tundra snow, melt differently because both snow pack structures and climatic patterns differ in the two zones. However, common to all climate zones, the snow pack must transition through several critical hydrologic states before it is all melted: dry snow; surface-wetted snow; mostly dry snow with percolation to the base; fully wetted snow with grain-coarsening; water (or ice) ponding at base, and so on.

2. Integrated Regional Analyses of Snowmelt Processes Across Northern Alaska The purpose of this project was to begin the work of extrapolation of our knowledge of hydrologic processes across broad areas of the Alaskan Arctic. The first goal of the experiment was to observe and record the timing of the critical melt transitions of the snow pack across as wide a range of climatic conditions as possible, and to quantify how these transitions vary as a function of the energy balance and the snow stratigraphy. The second goal was to use the data collected at the widespread sites to assess how well different remote-sensing platforms can determine the sequence of critical transitions in the snow during the melt at a regional scale. The proposed "experiment" is timely; we are entering the extrapolation phase of the ATLAS project and such an integrated and collaborative effort will provide the means to extend our measurements and understanding across broad areas. Funded projects had investigators in the field at Ivotuk, Imnavait Creek, Barrow, Prudhoe Bay, Council, Kougarok, and Caribou Poker Creeks. There were also a number of projects funded to look at snowmelt in Alaska using remote sensing. Now, the plan is to develop a set of common protocols for measurements so that ground-based data will be readily comparable, and to ensure that all key snow and weather parameters are recorded.

3. Scenes from Ivotu

4. . . The wind plays a major role in snow distribution throughout Alaska.

5. Windspeed and other climatic variables are monitored at every target site where ablation processes will be monitored.

6. Snowpack distribution and melt rate is largely controlled by meteorological conditions, topography and vegetation.

7. (cm) Snowpack ablation during spring, 1999 displays remarkable variability among the many sites where snowmelt processes were monitored.

8. The spring 2000 snowmelt was unusually late all across Alaska. The spring 2000 snowmelt was typical for Resolute, Canada

9. Snowpack ablation has been monitored for many years in Imnavait Watershed, demonstrating that interannual variability at one site may be nearly as great as spatial variability across northern Alaska.

10. Shrubs can trap great depths of snow, making locomotion for wildlife and scientists very difficult. However, the greater depth of snow also provides much greater insulation from the cold winter air, perhaps making these shrub areas more habitable for rodents and lessening the probability of over-winter desiccation or frost damage of plants. The shrubs also hold the snow in the riparian areas along stream channels, yielding greater proportions of spring snowmelt runoff as compared to tussock tundra areas.

11. The arctic tundra is covered with snow for 8 to 9 months each year. This persistent snow cover directly or indirectly impacts most physical and biological processes. Even analyses of summer-time hydrologic and thermal processes must rely upon firm understanding of the precursor winter conditions. Snow distribution is one of the dominant controls of winter heat flux from the surface. This winter heat loss will be one of the controlling factors on the depth of the active layer in the following summer. This can directly impact vegetation survival, soil moisture levels and erosion of soil. The amount and distribution of snow also controls the timing of spring snowmelt on many scales and the volume and intensity of snowmelt runoff.

12. Funding for this research was provided by the National Science Foundation Arctic Systems Science Program Grant No. OPP-9818066,Larry Hinzman Water and Environmental Research Center, University of Alaska Grant No. OPP-9732077,Matthew Sturm Cold Regions Research and Engineering Laboratory, US Army

13. Larry Hinzman ffldh@uaf.edu Matthew Sturm msturm@crrel.usace.army.mil