An Inventory of Canadian Rocky Mountain Glaciers

A 2011 study has found that between 1985 and 2005, Alberta and British Columbia have lost 11% of their glaciated area, while the Albertan Rocky Mountains have lost over 20%. By modeling future weather conditions, and glacier behavior, the study predicts that the Albertan Rocky Mountains will lose between 80-90% of their volume by 2100. This has potentially huge implications for water management, tourism, and ecosystem change, but perhaps most notably; it gives us a glimpse at what the future of the Rocky Mountains will look like under modern anthropogenic climate change.

Glaciated areas were put together using aerial photographs, as well as Landsat TM5 satellite imagery from 1982-1988 and again between 2004 and 2006. Focusing on the Rocky Mountain glaciers that flow eastward from the continental divide, this dataset allows us to uncover some particularly important points about the nature of our glaciers.

Size Range (km2) Glacier Count Glacier Area (%)
0.05 – 0.1 165 1.3
0.1 – 0.5 525 13.1
0.5 – 1.0 150 11.1
1.0  – 10 154 42.3
10 – 40 16 32.3

Table 1: 2005 Rocky Mountains (Eastern Slopes), adapted from Marshall et al. (2011)

The vast majority of glaciated areas in the Rockies are contained within a few large glaciers. Of note, there are actually more glaciers in 2005 than there were in 1985 (1010 vs. 926), even though we have lost roughly 25% of the glaciated area during the same period. This should give us an idea of the “life-cycle” of a continental glacier, where larger glaciers become fragmented as they shrink.

Now, although losing glaciated area is indicative of warming, as people concerned with the water resources these glaciers house, we should be more concerned with volumetric changes. Unfortunately, it’s a lot more difficult to measure glacier volume than area. For individual glaciers, a full survey of the glacier using ice penetrating radar can give you a pretty good idea of the bed topography, which you can then turn into a digital elevation model. As you can imagine, this is a very time-consuming endeavor, and isn’t practical to do for every glacier in the Cordillera. Instead, from periodically surveyed benchmark glaciers, we can form an empirical best fit relation between glacier area and volume, known as Volume-Area Scaling. Unfortunately, the number of glaciers in the Rockies that have been surveyed is only small (Rae, Athabasca, Haig, Peyto). The volume numbers are hardly definitive, however, they still give us a pretty good idea of how much ice is left.

In total, the authors use 4 methods to calculate glacier volume (regional and global relations for Volume-Area Scaling, a model that relates ice thickness to averaged and local slopes). These methods give us an average value of 55 km2 of ice left in the Rockies, 48% of which is contained in the largest 10 glaciers.

pic1

From Marshall et al 2011

Of course, the key here is what we should expect to see going forward. If this century were to experience glacier retreat similar to what we have seen in the 2000s (an optimistic scenario), the authors expect we would lose about 40% of present day glacier ice. However, if IPCC projections A1b and B1 are assumed, the authors warn that we should expect to lose between 80 and 90% of current glacier volume this century.

So if we are in fact predicting the demise of a large portion of Rocky Mountain glaciers, how does that impact the day to day in Alberta? One of the primary worries of glacier melt is the effect it will have on river systems. Right now, glaciers in the North Saskatchewan River and Bow River basins supply about 4% of the total river discharge, while between July and September glaciers that figure doubles. According to projections of ice loss, we should expect Albertan glaciers to be making about one tenth of their current contributions by the end of the century, with the vast majority of this deficit felt late in the summer.

pic2

From Marshall et al. 2011

Now, losing 8% of out river flow is hardly a “scorched-earth” type scenario, but the water that these glaciers provide is still an important part of rivers, and ecosystems. They are an important background supplier of flow, help regulate water temperatures, and contribute sediment that helps regulate water systems.  Although there is uncertainty as to the amount of ice we may lose this century, it is clear that even best-case scenarios call for a substantial glacier melt and a significant reduction in glacier contributions to stream flow.

For more reading, see:

Marshall, Shawn, et al. “Glacier water resources on the eastern slopes of the Canadian Rocky Mountains.” Canadian Water Resources Journal 36.2 (2011): 109-134.

Alberta Water, Glacier Inventory and Ice Volume Estimation

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