The lowdown on the flows

Despite predictions that under a warming scenario, melt-water contributions from glaciers would increase in the long term, water flows from glacier-fed rivers are already decreasing. Drastic reductions in the surface area of glaciers in the last century have resulted in reduced downstream water flows, despite the increased melt rates brought on by changing precipitation patterns in winter and the general warming experienced over the past several decades. It is still uncertain, however, to what degree these observed reductions are a result of an overall adjustment of the glacier cover after the "Little Ice Age" maximum (ca. AD 1850), or of more recent climate change.

Athabasca glacier in 1917. (Alberta/BC Provincial Boundary Commission)

Athabasca glacier in 1986. Climate change could result in significant retreat of large glaciers such as this, and related reduction in downstream water flows, wildlife habitat, and hydroelectricity production. (B.H. Luckman)

Impacts - fisheries habitat

Bull Trout (Paul Hvenegaard, Alberta Conservation Association)

The glacier meltwater helps preserve the habitat for aquatic species that are highly adapted to cool mountain streams. Glacier meltwaters maintain water levels and habitat that enable trout to migrate and spawn in the late summer and autumn. A reduction in glacier-derived flows during this period may already be having a serious impact on the Bull Trout population.

Impacts - reservoirs

Seasonal runoff from basins containing glaciers is characterized by longer snowmelt runoff seasons, higher discharge volumes, and peak concentrations of runoff in summer months, compared to basins without glaciers. The glaciers act as storage reservoirs that benefit downstream regions in summer months. They also act as a source of disturbance, such as when rain-on-ice persists for several days, causing extremely high flows, erosion, and flooding.

Typical glacier-fed stream flow (Source: Mike Demuth, pers. comm. , 2000)

Did you know?
There are more than 1300 glaciers in the eastern slopes of the Rocky Mountains.

References

Milner, A.M. and Petts, G.E., 1994: Glacial rivers: physical habitat and ecology; Freshwater Biology, v. 32, p. 295 - 307.

M.N. Demuth (Geological Survey of Canada - National Glaciology Programme) and A. Pietroniro (National Water Research Institute - Aquatic Ecosystem Impacts Branch) pers. comm.