Regional Modeling of the Glaciers of the North Cascades Mountains, Washington, USA
Glaciers in the North Cascades store winter snowfall as ice and release it in late summer as melt, providing an important regional source of water and hydroelectric energy. The future of glaciers in the North Cascades, Washington, were evaluated using a regional glaciation model driven by the Community Climate System Model 4 global climate model. The climate model was coupled with three Representative Concentration Pathways (RCPs), 2.6, 4.5, and 8.5. These RCPs provide a business-as-usual scenario (RCP 8.5), which assumes society makes little to no efforts to reduce greenhouse gas emissions, a best-case scenario (RCP 2.6) with strong attempts to mitigate greenhouse gas emissions, and a moderate scenario (RCP 4.5). Spun up from 850 C.E., modeled glacier area for 1970 was 96-102% of observed. By 2100 the predicted area relative to the total observed area in 1900 was 42% for RCP 2.6, 16% for RCP 45, and 5% for RCP 8.5. By 2100 only glaciers on high peaks, such as Mt. Baker and Glacier Peak, will remain (145.98 km2 , RCP 2.6; 70.49 km2 , RCP 4.5; 16.82 km2 , RCP 8.5) and entirely gone by 2200 in any of the three climate scenarios
Modeling of the Sensitivity of Glaciers in the Pacific Northwest and their Response to Climate Change
Glacial melt rivers feed into local drainage basins and power hydroelectric energy. Melted ice will feed into the local water supply, so as glaciers retreat the glacial discharge will increase. However after an initial surge in melt water the amount of glacier ice will lessen, as will the amount of water available for consumption, making it important to understand how glaciers respond to climate warming to understand the future of water for the nearby localities (Bennett and Glasser, 2009).
To do this a model can be used to observe how physical factors such as width variations, slope, and headwall elevation are related to a glacier’s sensitivity to climate change. A steady state, width-varying flow line model will be used to model glaciers on Mount Rainier and in the North Cascades National Park and observe how different characteristics cause some glaciers to have lower mass balances than others (Huybers, personal communication).
Higher headwall elevations, larger lapse rates, steeper slopes, and glaciers that end in a narrow tongue are related to glaciers that are less sensitive to climate, whereas lower headwall elevations, gentler slopes, and channel like width variation are related to more sensitive glaciers. Since glaciers in the North Cascades are lower altitude with gentler bed slopes than Mount Rainier glaciers and have weaker width variations or variations that open up, they are more likely to respond strongly to climate change.
Modeling Pacific Northwest Glaciers with Differential Equations
Glaciers are extremely dependent on climate, and small increases in temperature can cause changes in glacier size. Understanding what physical characteristics of glaciers, such as headwall elevation, slope, and width variations affect how a glacier's size changes in response to climate change is important since the localities around these glaciers rely on them for water, as well as hydroelectric energy (Bennett and Glasser, 2009).
In this study a model based on equations from the shallow ice approximation (Huybers, personal communication) was used to describe changes in glacier size for glaciers in the North Cascades and Mount Rainier National Parks. From the model we can see that higher headwall elevations, steeper bed slopes, and narrowing width variations contribute to lessening glacier sensitivity, potentially explaining why the Mount Rainier glaciers are less sensitive than North Cascade glaciers.
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Bennett M., and N. Glasser, (2009) Glacial Geology: Ice sheets and landforms, 2nd ed. Wiley-Blackwell, Chichester, UK
Clarke, G., Jarosch, H., Anslow F., Radic V., and B. Menounos, (2015), Projected deglaciation of western Canada in the twenty-first century, Nature Geoscience (8), 373-377, doi: 10.1038/ngeo2407
Huybers, K. (2016), personal communication
Menounos, B. (2017), personal communication