Jun 26, 2012
Insight: streamflows intensify in the Fraser River Basin
The Fraser River Basin, an important watershed in western North America, is experiencing greater year-to-year fluctuations in streamflow than ever before. These variations are impacting salmon returns, as well as the transport of sediments, nutrients, carbon and contaminants. Overall water quality is also being affected.
The Fraser River is the largest Canadian waterway flowing to the Pacific Ocean and is one of the world's greatest salmon rivers. Indeed, five species of salmon populate the Fraser and up-river migrations of the fish may be being influenced by greater fluctuations in streamflow. Low flows are often associated with warmer water temperatures whereas high flows accompany strong currents but an extreme in either of these situations is detrimental to migrating and spawning salmon. Impacts on these keystone species are of concern for the many First Nations communities and to the important commercial and recreational fisheries of the Fraser River Basin.
In this study, streamflow data for 139 sites situated across the Fraser River Basin were extracted and analysed for regional patterns in areal runoff productivity and variability. The study period covered a full century (1911–2010) although data availability varied markedly across the basin. The results revealed greater runoff productivity and lower runoff variability in headwater and coastal catchments compared to those in the central portions of the Fraser River Basin. Central portions of the basin lying in the rain shadow of British Columbia's Coast Mountains appeared to have experienced relatively low precipitation amounts compared to headwater and coastal watersheds where abundant snowmelt and late-summer glacial melt moderate year-to-year runoff fluctuations.
A trend analysis revealed increasing variability in annual streamflow over time, with more prominent changes in spring and summer across the basin. As the climate continues to warm, greater variability in streamflow, and hence in hydrological extremes, may influence ecological processes and how the Fraser River Basin is used in the 21st century.
About the author
Stephen Déry holds a Canada Research Chair in Northern Hydrometeorology and has appointments as associate professor in the Environmental Science and Engineering Undergraduate Program and the Natural Resources and Environmental Studies Graduate Program at the University of Northern British Columbia (UNBC). Marco Hernández-Henríquez contributed to the article as a research assistant with Stephen Déry and the other authors who are part of UNBC's Integrated Watershed-based Science Group.