Climate in the Lake Winnipeg Watershed and the Level of Lake Winnipeg. Gregory K. McCullough

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1 Climate in the Lake Winnipeg Watershed and the Level of Lake Winnipeg Prepared at the request of the Manitoba Clean Environment Commission Gregory K. McCullough 16 March 215

2 Historical climate and runoff Predicted climate and runoff Lake level Temperature Precipitation River discharge Greg McCullough CEC 16 March 215 2

3 Historical climate and runoff Temperature Precipitation River discharge Greg McCullough CEC 16 March 215 3

4 o C The Pas A Dauphin A Brandon CDA Morden CDA Great Falls Kenora A July-August temperature at selected weather stations near Lake Winnipeg expressed as the difference from the average for the period AHCCD data, corrected for instrument & station changes.

5 Monthly mean surface water temperature in Lake Winnipeg left: as a function of mean air temperature in the same month right : estimated as a function of the current and previous monthly mean air temperatures Greg McCullough CEC 16 March 215 5

6 Historical climate and runoff Temperature Precipitation River discharge Greg McCullough CEC 16 March 215 6

mm/y mm/y mm/y mm/y mm/y mm/y 12 9 9 6 3 SW Alberta +14% 9189 194 199 6 3 S Manitoba, N North Dakota +13% 12189 194 199 6 3 N Saskatchewan +12% 9189 194 199 9 6 3 S Dakota, NW Minnesota +9% 12189 194

7 mm/y mm/y mm/y mm/y mm/y mm/y SW Alberta +14% S Manitoba, N North Dakota +13% N Saskatchewan +12% S Dakota, NW Minnesota +9% S Saskatchewan % NW Ontario +8% Annual precipitation at selected stations in the Lake Winnipeg watershed Each point is the average at 2 3 nearby stations Values in red are % change per century At left: Locations of clusters of station with long term records corrected for instrument and station changes. (Source: AHCCD) Greg McCullough CEC 16 March 215 7

8 Seasonal precipitation and annual stream flow changes in the Lake Winnipeg watershed. Circle diameters show precipitation and discharge as percent change from the average for Red indicates increases; blue indicates decreases. Greg McCullough CEC 16 March 215 8

9 Historical climate and runoff Temperature Precipitation River discharge Greg McCullough CEC 16 March 215 9

10 Relative discharge 1% 8% 6% 4% 2% % Dauphin R Saskatchewan R Red R Winnipeg R Relative contribution of the major tributaries to inflow to Lake Winnipeg Greg McCullough CEC 16 March 215 1

11 Discharge (cfs) Discharge (cfs) Discharge (cfs) Discharge (cfs) 6 Saskatchewan R -19% 15 Dauphin R +95% Red R % Delta Winnipeg R +53% Annual discharge of major tributaries of Lake Winnipeg Values in red/blue are % change per century. Emerson At left: Water Survey of Canada stations used to reconstruct continuous inflow records. Greg McCullough CEC 16 March

12 A 2% difference in precipitation, from 55 to 66 mm/y, more than doubles the runoff, from 5 to 11 mm/y, over the eastern Red River watershed Greg McCullough CEC 16 March

13 Discharge (cfs) Pacific Decadal Oscillation Total inflow PDO Annual total inflow to Lake Winnipeg compared with the historical pattern of the Pacific Decadal Oscillation 1 2 Greg McCullough CEC 16 March

14 Historical climate and runoff Predicted climate and runoff Lake level Temperature Precipitation River discharge Greg McCullough CEC 16 March

15 Predicted monthly mean surface water temperature in Lake Winnipeg in 25 and 29 Scenarios B1, A1B and A2 describe evolution of greenhouse gas concentrations and aerosol loadings in order of increasing effects of population growth, economic development and technological change over the next century. Greg McCullough CEC 16 March

16 Ice melt/break-up Freeze-up Predicted timing of ice break-up and freeze-up on Lake Winnipeg in 25 and 29 Scenarios B1, A1B and A2 describe evolution of greenhouse gas concentrations and aerosol loadings in order of increasing effects of population growth, economic development and technological change over the next century. Greg McCullough CEC 16 March

17 Temperature ( o C) and precipitation (%) changes predicted for grasslands and forest regions in the Canadian Prairie Provinces. Temperature Precipitation Grasslands Forest Grasslands Forest Winter 25s Spring 25s Summer 25s Autumn 25s Annual 25s Annual 28s Source: Natural Resources Canada study synthesizing results from 7 global climate models X greenhouse gas emissions scenarios. (Sauchyn and Kulshreshtha 29) Greg McCullough CEC 16 March

18 Source: Natural Resources Canada study synthesizing results from 7 global climate models X greenhouse gas emissions scenarios. (Sauchyn and Kulshreshtha 29) Greg McCullough CEC 16 March

19 hange ean per cent 4 hange 2 Mean per cent change in runoff ean per cent -21 hange ean per cent Agreement among models tested Predicted change in runoff in compared with average runoff from Source: Milly et al. 25. Greg McCullough CEC 16 March

20 Greg McCullough CEC 16 March 215 2

21 Historical climate and runoff Predicted climate and runoff Lake level Temperature Precipitation River discharge Greg McCullough CEC 16 March

22 ft ft ASL ASL el l min. min. level level mean mean leve min. level mean min. min. level level max. mean mean level level level max. min. max. level level mean min. level max. level Annual min., mean and max. water level in Lake Winnipeg, Setup was removed prior to calculating annual min. and max. values, by calculating the running weekly mean level at two stations, one each in the north and south basin. Greg McCullough CEC 16 March

23 Annual peak water level as a function of total inflow Setup has been removed from the recorded water level set. Estimated peak lake level was determined by regression on 1) the mean inflow for the 12-months prior to April, and 2) the highest monthly mean inflow in the current year. Greg McCullough CEC 16 March

24 Isostatic rebound, climate and regulation Without regulation, Lake Winnipeg would have been two feet higher, averaged from , than at the beginning of the record. Isostatic rebound explains.7 ft/century of rise in the water level (of the south basin). Higher total flow from tributary watershed explains the balance. From , regulation effectively prevented a average of 1.1 ft of the expected increase of Lake Winnipeg levels due to the combined effect of isostatic rebound and climate. Water level (ft. ASL) regulated 714. unregulated Rise/century +2.1 Greg McCullough CEC 16 March

25 Water level (m A.S.L.) Setup-free level Hourly mean level Daily mean level Relationships between hourly and daily mean level recorded at Gimli, and the setup-free water level of Lake Winnipeg Greg McCullough CEC 16 March

26 Setups/year Setup (ft) Maximum setup Median of 1 highest setup events 2 Frequency of >1 ft setup events 1 Record of daily mean setup events in the south basin Setup calculated as the difference between the daily mean water level at Gimli (or Winnipeg Beach before 1966) and the previous median level measured over the previous week. Hourly mean water level along the south shore could be more than two feet higher than the daily mean level. Greg McCullough CEC 16 March

27 Water level (ft MSL) Water level (ft) MSL Maximum setup-free level Setup Water level at maximum setup Water level + maximum setup Maximum daily mean setup events in the south basin The highest setup events rarely coincide with the highest (setup-free) lake levels. Upper chart: Record of annual peak water level, showing the contribution of setup to the level at Gimli. Lower chart: Record of highest annual setup events, showing the water level at Gimli at the time of each event. Greg McCullough CEC 16 March

28 Frequency (%) Frequency (%) Frequency (%) foot setup foot 12setup Daily mean setup at Gimli Setup calculated as the difference between the daily mean water level measured at Gimli (or Winnipeg Beach before 1966) and the previous median level measured over the previous week. Hourly mean water level along the south shore could be more than two feet higher than the daily mean level measured at Gimli. Greg McCullough CEC 16 March

29 Monthly mean outflow discharge (cfs) Monthly mean outflow discharge (cfs) 2, 16, Jan-Apr Jan-Apr , 16, Jun-Nov Jun-Nov , 12, 8, 8, 4, 4, Monthly mean water level (ft MSL) Monthly mean water level (ft MSL) Winter Summer Outflow of Lake Winnipeg as a function of lake level. Greg McCullough CEC 16 March

30 Water level (ft ASL) Water level (ft ASL) Unregulated (modeled) Unregulated (modeled) Regulated (observed) Regulated (obs +/- error (2 X s.d.) +/- error (2 X s.d.) +/- setup +/- setup Observed min., max. Observed min., max. Regulated water level Recorded annual mean water level (heaviest blue line) plus/minus 95% confidence limits of the model (mid-weight blue lines) and the added effect of setup (light blue lines). The recorded annual minimum and maximum levels fall near the sum of the mean +/- model uncertainty +/- setup. Greg McCullough CEC 16 March 215 3

31 Water level (ft ASL) Regulated (observed) +/- error (2 X s.d.) +/- setup Unregulated (modeled) Regulated vs. unregulated water level Unregulated (modeled) annual mean water level (heaviest blue line) with 95% confidence limits of the model (mid-weight blue lines) and the added effect of setup (light blue lines). Greg McCullough CEC 16 March

32 Summary precipitation and inflow Average annual total inflow to Lake Winnipeg has ranged by almost 4X from 35, to 136, cfs. Over the 2 th century in the Winnipeg and Red River watersheds precipitation and outflow have increased in the Saskatchewan R watershed, precipitation has not changed significantly, but flow has decreased For the 21 st century, on balance, models predict in the Winnipeg and Red R watersheds, moderate increases in precipitation that will be magnified into larger increases in runoff in the Saskatchewan, either no change or drying, with little change in runoff All Lake Winnipeg sub-watersheds are marked decadal and longer wet and dry periods causing variability in runoff that exceeds historical or predicted century scale trends Greg McCullough CEC 16 March

33 Summary lake level Daily mean setup-free water level of Lake Winnipeg has ranged from 79.2 to ft ASL. In the south basin, setup has added over 2 ft to the top of this range. The water level record in Lake Winnipeg is marked by a succession of extended high and low water periods. Lake Winnipeg is now on average 1 ft higher than in the early 2 th century Without regulation, the combined effect of isostatic rebound and increased flow from tributary watersheds would have been to increase lake levels by another ft higher. If predicted increases in precipitation and runoff in the Winnipeg and Red R watersheds are borne out, it will be increasingly difficult to manage Lake Winnipeg below 715 ft. ASL. Greg McCullough CEC 16 March

SWAN LAKE INTEGRATED WATERSHED MANAGEMENT PLAN SURFACE WATER HYDROLOGY REPORT 1

SWAN LAKE INTEGRATED WATERSHED MANAGEMENT PLAN SURFACE WATER HYDROLOGY REPORT 1 1. General Description Figure 1 provides a map of the Swan Lake Watershed. The watershed is characterized by two major parallel