Assessing the Frequency, Severity and Causes of Extreme Droughts and Low Flows in the Winnipeg River Basin

Activity Rationale

tree-ring data

Changing hydrological conditions are the largest risk faced by hydroelectric power generators in Canada. This activity uses long river records and tree-ring data to help understand drought in the Winnipeg River, a key element of the hydroelectric power system in Manitoba.

Leader: Scott St. George

The Topic

The Winnipeg River begins at the northern end of Lake of the Woods and terminates in the south basin of Lake Winnipeg. The river is the single largest source of water to Lake Winnipeg, and influences the production of over 4600 megawatts of hydroelectricity in Manitoba and Ontario. Understanding the behavior of this river and the frequency and magnitude of hydrological drought is directly relevant to hydropower planning in northwestern Ontario and Manitoba.

The Winnipeg River is the largest river in the southern Prairies and an important source of water for hydroelectricity
The Winnipeg River is the largest river in the southern Prairies and an important source of water for hydroelectricity
Scientists from the Geological Survey of Canada collect samples from red pines near Gordon Lake, Ontario.
Scientists from the Geological Survey of Canada collect samples from red pines near Gordon Lake, Ontario.

Many geological or biological systems, including trees, lakes and glaciers, contain a detailed record of past environmental conditions and events. Paleohydrology uses 'proxy data' derived from these natural archives to describe how rivers, lakes and groundwater resources behaved during earlier periods of the Earth's history. In this activity, scientists have used tree-ring records from the Winnipeg River watershed to describe how drought has changed over the last several centuries, and how river flow in the Winnipeg River has changed during the last 100 years.

Results

Tree rings describe past drought

Studying the tree-ring record in a windblown red pine, Quetico Provincial Park, Ontario.
Studying the tree-ring record in a windblown red pine, Quetico Provincial Park, Ontario.

The tree-ring records demonstrate that the most severe droughts since the mid-1700s occurred during the 20th century, and indicate that current worst-case scenarios for drought in the Winnipeg River are likely adequate to forecast future drought risks. In contrast, tree rings show that other parts of the Canadian Prairies were recently affected by summer droughts more intense and long-lasting than those described by instrumental records. These findings contribute to improved assessments of total water resources and more accurate worst-case scenarios for water resources management.

More water in the Winnipeg River

Although the flow of many Prairie rivers has declined over the last few decades, the Winnipeg River does not follow this regional trend.  Instead, the discharge of the Winnipeg River has increased substantially since the early 20th century.  These results suggest that declining river flows observed in the western Prairie Provinces are being offset by increasing runoff in Manitoba and northwestern Ontario.  The study also showed that extreme low flows are caused by severe reductions in runoff from spring snowmelt, and follow dry weather over much of the basin during the previous summer and autumn.  These observations represent an important contribution to ongoing discussions on the reliability of water resources on the Canadian Prairies, and may be useful to improve short-term predictions of severe drought.

Study Data

St. George, S. et al., 2008.  Winnipeg River basin regional ringwidth series.  IGBP-PAGES World Data Center for Paleoclimatology Data Contribution Series #2008-065.  NOAA/NGDC Paleoclimatology Program. Boulder, CO, USA.   http://www.ncdc.noaa.gov/paleo/pubs/stgeorge2008/stgeorge2008.html

Publications

Please note that subscriptions may be required for access to some articles. To request a copy of publications, or for any more information, please contact
Scott St. George.

Check for more recent publications in GEOSCAN, the publications database of the Geological Survey of Canada and the Canada Centre for Remote Sensing.

St. George, S., Meko, D.M., Girardin, M.P., Nielsen, E., Pederson, G., Sauchyn, D.J., Tardif, J. and Watson, E.  (accepted).  The tree-ring record of summer drought in the Canadian Prairies.  Journal of Climate.

St. George, S., Meko, D.M. and Evans, M.E. 2008. Regional tree growth and inferred summer climate in the Winnipeg River basin, Canada since AD 1783.  Quaternary Research 70, 158-172.  http://dx.doi.org/10.1016/j.yqres.2008.04.009

St. George, S. 2007.  Streamflow in the Winnipeg River basin, Canada: trends, extremes and climate linkages.  Journal of Hydrology 332, 396-411.  http://dx.doi.org/10.1016/j.jhydrol.2006.07.014

St. George, S., and Sauchyn, D.J. 2006.  Paleoenvironmental perspectives on drought in western Canada – Introduction.  Canadian Water Resources Journal 31, 197 – 204. 
http://pubs.nrc-cnrc.gc.ca/cwrj/cwrj4-06.html

 

Other Materials

St. George, S., Sauchyn, D.J, Halliday, R., and Cumming, B.F. 2008.  Workshop report: paleohydrology and water resources on the Canadian Prairies.  Canadian Water Resources Association Water News.

St. George, S. and Meko, D.M. 2007: Using tree-ring data to understand summer drought in a key watershed for Manitoba Hydro; in Report of Activities 2007, Manitoba Science, Technology, Energy and Mines, Manitoba Geological Survey, p. 155–160.

St. George, S. 2006.  Hydrological dynamics in the Winnipeg River basin, Manitoba. in Report of Activities 2006, Manitoba Science, Technology, Energy and Mines, Manitoba Geological Survey, p. 226-230.

St. George, S.  2005.  A new tree-ring network for studying drought in southeastern Manitoba and northwestern Ontario; in Report of Activities 2005. Manitoba Industry, Economic Development and Mines, Manitoba Geological Survey, p. 164 – 166.