This indicator tracks the trends in winter flows in selected rivers of the NWT.
Cameron Falls in winter, Taiga Shield. © S. Carrière
Winter flows are reported for 13 rivers in the NWT, organized by ecozone and catchment area. Winter flows are calculated by averaging the November to April monthly data, expressed in cubic meters per second. Trends in winter flows are estimated using decade averages. Catchment area is total drainage area of a river above the gauge site.
Some of the larger rivers include tributary sub-catchments for several ecozones. All the selected rivers have natural flow regimes without any artificial controls and generally have data records of 30 to 40 years. For more information on a regulated river, the Slave, see Indicator 11.2.
Data are obtained from the Water Survey of Canada Hydat website1 and graphs and analysis are by GNWT, Water Resources Division.
In the NWT, as in most northern regions, the lowest stream flows occurs during winter2. Summer flows can be many times higher than winter flows (see hydrograph for Peel River below). Adequate winter flows are important for overwintering fish, providing habitat with water temperatures and dissolved oxygen levels sufficient for fish survival3.
Daily mean flow (cubic metre per second) obtained from the Peel River for year 1969-2013. Multi-year average of daily flow is shown as MEAN (black line).
Current view - status and trend
In general, using decade averages, winter flow show increasing trends across all ecozones, and for large and small basins alike. The Cordillera and Taiga Plains rivers show small increases between the 1970s and 1980s and larger increases in the 1990s and 2000s over a range of catchment sizes. The two Taiga Shield Rivers (Cameron River and Baker Creek) are relatively small and have a shorter period of record but show large increases in the decade average in the 2000s. The Southern Arctic (Tundra Shield) rivers are relatively stable through the 1970s to the 1990s with an increase in winter flows apparent in the 2000s. The larger rivers, such as the Mackenzie River with tributary inflows from more than one ecozone, also show increasing winter flows based on decade averages by also possibly show some cyclical patterns.
Although the decade averages indicate an increasing trend in winter flow, rigorous statistical analyses were not done with the data for this indicator. Statistical analyses of flow gauge data are available and confirm the trends shown above. Strong increasing trends of winter flow are noted in the Mackenzie Basin1 and the Peel Watershed4. There is evidence the rate of increase in winter low flows may have been higher two decades ago (period prior to 1983) than recently4.
The timing of winter low flows has changed during the past 50 years. Ehsanzadeh and Adamowski (2010)5 found that the seven-day window of low flows is occurring later in winter in recent years for most areas north of 60 between the Yukon and the Hudson Bay5,6,7.
Possible reasons for increasing winter flows could be increased autumn rainfall and/or warmer autumn and winter temperatures that delay ground freezing. Changes in groundwater contribution (from hot or warm springs may also affect winter flows in rivers in the Cordillera8.
Monk and Baird (2010)7 have compiled trend information from a number of sources for the "Canadian Biodiversity: Ecosystem Status and Trends Report"6 and have identified similar trends in winter flows in tributaries of the Mackenzie River. Note that the minimum river flows in northern Canada occur in winter but in southern Canada they occur at the end of summer. Both significant increases in winter low flows in the north and significant decreases in summer low flow in the south are consistent with what is expected in a warmer climate.
Trends in minimal river flow in natural rivers (1970-2005) reproduced from the Canadian Biodiversity: Ecosystem Status and Trends Report6, based on Monk and Baird (2010)7.
Further investigation of the cause(s) is warranted, including possible links between these trends and decade fluctuations9,10,11 and climate change2. Climate change forecasts for the Mackenzie River Basin predict further increases in temperature and increases in precipitation (see THE BIG PICTURE: A CHANGING PLANET focal point). As this occurs, it is expect the increasing trend in winter stream flows will continue.
- Data on river flow, Water Survey of Canada, HYDAT
- Lakes and river trends in Canada, Canadian Biodiversity: Ecosystem Status and Trends Report
All results and analyses reported in this indicator are limited to areas south of the 70oN, as long-term gauge data are not available for rivers north of that latitude. A summary of how trend analyses on river flows are performed is provided in Ehsanzadeh eh al (2011)4, and references therein. For more information on how stream flows are monitored by the Water Survey of Canada NWT/NU Hydrometric Network. Locations of gauges in the NWT and Nunavut, as of 2013-14 season are shown on the map below.
Found an error or have a question? Contact the team at NWTSOER@gov.nt.ca.
Ref. 1. Water Survey of Canada.
Ref. 2. Burn, D.H., H.A. Shaverdo, and K. Zhang. 2010. Detection of trends in hydrological extremes for Candian watersheds. Hydrol Process 24:1790.
Ref. 3. Brown, R.S., W.A. Hubert, and S.F. Daly. 2011. A primer on winter, ice and fish: what fisheries biologists should know about winter ice processes and stream-dwelling fish. Fisheries 36:8-26.
Ref. 4. Ehsanzadeh, E., T.B.M.J. Ouarda, and H.M Saley. 2011. A simultaneous analysis of gradual and abrupt changes in Canadian low stream flows. Hydrol Process 25:727-739.
Ref. 5. Ehsanzadeh, E., and K. Adamowski. 2010. Trends in timing of low stream flows in Canada: impact autocorrelation and long-term persistence. Hydrol Process 24:970-980.
Ref. 6. Federal, Provincial, and Territorial Governments. 2010. Canadian biodiversity: ecosystem status and trends 2010. Canadian Councils of Resource Ministers. Ottawa, ON.
Ref. 7. Monk, W.A., and D.J. Baird. 2010. Ecosystem status and trends report: biodiversity in Canadian lakes and rivers. Canadian biodiversity: ecosystem status and trends 2010 technical thematic report No. 20.
Ref. 8. Clark, I.D., B. Lauriol, L. Harwood, and M. Marschner. 2001. Groundwater contributions to discharge in a permafrost setting, Big Fish River, NWT, Canada. Arctic, Antarctica, and Alpine Research 33:62-69.
Ref. 9. Brabets, T.P., and M.A. Walwood. 2009. Trends in stream flow in the Yukon River basin from 1944 to 2005 and the influence of the Pacific Decadal Oscillation. Journal of Hydrology 371: 108-119.
Ref. 10. Déry, S.J., and E.F. Wood. 2005. Decreasing river discharge in northern Canada. Geophysical Research Letters 32:L10401.
Ref. 11. Wang, J.Y., and P.H.C.A.J. Whitfield. 2006. Influence of Pacific climate patterns on low-flows in British Columbia and Yukon, Canada. Canadian Water Resources Journal 33:25-40.
Updated: May 28, 2015