This research will provide paleo-hydrologic data for use by hydro utility companies to help predict effects of hydrologic variability. The research includes new instrumental and proxy climate networks, conducted under a funding agreement with Manitoba Hydro, that will provide primary data necessary to determine past hydroclimatic change in the Winnipeg River basin.

For more information:
Scott St. George

Introduction

Water power is the pre-eminent source of electricity produced in the eastern Canadian Prairies. In Manitoba, hydroelectric generating stations on the Nelson, Winnipeg and Saskatchewan rivers produce roughly 30 billion kilowatt-hours of electricity each year (Manitoba Hydro, 2005). This power represents both a renewable supply of energy, and a reliable revenue source through the export of electricity to other provinces and the United States. Because the amount of electricity produced by hydroelectric generation stations is controlled by the quantity of water flowing through the system, widespread and severe drought can create significant reductions in available energy, and attendant decreases in revenue.

This project examines the nature of drought in the Winnipeg River basin (Fig. 1), which is a key component of the hydrological system used to generate electricity in Manitoba. A combination of instrumental gauge records and estimated flows inferred from tree-ring evidence will be used to assess how frequently droughts occur in the Winnipeg River basin, and whether or not the lowest observed inflows are accurate estimates of the maximum severity of basin-wide drought. This information will assist in determining how and why droughts develop, and in producing more realistic assessments of future drought risks.

Figure 1. The Winnipeg River (shown here immediately downstream of Lake of The Woods) contributes nearly half of the water flowing into Lake Winnipeg and the Nelson River. larger image [JPEG, 107.8 kb, 1600 X 344, notice]

The Winnipeg River basin

The Winnipeg River basin, which drains over 130 000 km2 in Ontario, Manitoba and Minnesota, is the most important component of the hydrological system used to generate power in Manitoba. Although it covers a relatively small area, the basin receives much more precipitation than areas to the west, and consequently provides nearly half (45%) of the water flowing into Lake Winnipeg and the Nelson River. The Winnipeg River currently supports six hydroelectric generating stations in Manitoba, which collectively produce 585 megawatts of electricity, roughly 11 percent of total provincial production. Because the river also is the largest source of water flowing into Lake Winnipeg, it thereby has an important influence on the production of nearly 4000 megawatts from the Jenpeg Generating Station and other stations on the Nelson River.

Using tree rings to understand past drought

Dendroclimatology uses data obtained from the annual growth rings of trees to study climatic conditions prior to the period of instrumental monitoring. Locally, tree-ring and limnological evidence has demonstrated that the northeastern Great Plains, including southern Manitoba, experienced prolonged arid conditions circa AD 1700 that lasted for nearly a century (St. George and Nielsen, 2002). Tree-ring data are particularly well suited to provide information on past hydrological conditions in the Winnipeg River basin because of the wide distribution of suitable forest sites, fine temporal data resolution and long records, as well as the clear relationship between tree growth and available moisture.

Field collections in 2004 and 2005 have established a new network of tree-ring sites in the Winnipeg River region, most of them falling in an area roughly demarcated by the communities of Kenora, Thunder Bay and Fort Frances in Ontario (Fig. 2). Sampling concentrated on the three longest-lived tree species in this area – eastern white pine (Pinus strobus), red pine (Pinus resinosa) and eastern white cedar (Thuja occidentalis). Preliminary ring counts of samples collected in 2004 indicate that tree-ring records from most trees span the last 120 years, with the oldest specimen being 255 years old (Fig. 3).

Figure 2. Locations of new tree-ring sites in the Winnipeg River area collected in 2004 (black) and 2005 (green), as well as earlier sites developed by other investigators (red). larger image [JPEG, 106.5 kb, 800 X 761, notice]

Figure 3. Red pine (Pinus resinosa) stump in Quetico Provincial Park, Ontario. Field estimates indicated that this tree was over 220 years old when it was toppled by a strong wind storm in July 2003. larger image [JPEG, 328.7 kb, 800 X 1067, notice]

Future work

Samples collected in 2005 will be prepared for analysis at the Laboratory of Tree-Ring Research, University of Arizona. These specimens, along with those collected in 2004, will be measured during the 2005/06 academic year, and the data generated will be used to characterise tree growth in the Winnipeg River region over the last two to three centuries. Subsequent analysis will determine if these data can be used to estimate the past occurrence and severity of drought in the Winnipeg River system, and place recent droughts within a longer context.

Acknowledgements

Fieldwork in southeastern Manitoba and northwestern Ontario was ably supported by J. Balmat, E. Nielsen and staff at the Manitoba Geological Survey. Sample preparation at the University of Arizona was performed by J. Rowland. Manitoba Conservation, Fisheries and Oceans Canada, the Ontario Ministry of Natural Resources and Fisheries and the Greenwood Lake Nature Reserve granted permission to collect dendrochronological samples within their respective jurisdictions. Information on the location of old-growth sites was graciously provided by C. Bowling, W. Carmine. R. Suffling, Abitibi Consolidated and the Ontario Ministry of Natural Resources. Financial support for this project is provided by Manitoba Hydro, the Manitoba Geological Survey, the Prairie Adaptation Research Collaborative and the National Science and Engineering Research Council of Canada.

References

Manitoba Hydro 2005: 2004/05 Annual Report. (available on-line at http://www.hydro.mb.ca/about_us/ar_2004/ar_2004_report.shtml).

St. George, S., and Nielsen, E. 2002: Hydroclimatic change in southern Manitoba since AD 1409 inferred from tree rings. Quaternary Research, v. 58, p. 103-111.