Presentation is loading. Please wait.

Presentation is loading. Please wait.

Canadian Prairie Hydrology and Runoff Generation John Pomeroy Centre for Hydrology, University of Saskatchewan, Saskatoon www.usask.ca/hydrology.

Similar presentations


Presentation on theme: "Canadian Prairie Hydrology and Runoff Generation John Pomeroy Centre for Hydrology, University of Saskatchewan, Saskatoon www.usask.ca/hydrology."— Presentation transcript:

1 Canadian Prairie Hydrology and Runoff Generation John Pomeroy Centre for Hydrology, University of Saskatchewan, Saskatoon

2 Prairie Hydrology Major river flow is primarily from mountain runoff, but prairie runoff supplies smaller rivers, streams, wetlands, and lakes Major river flow is primarily from mountain runoff, but prairie runoff supplies smaller rivers, streams, wetlands, and lakes Prairie Runoff Prairie Runoff forms in internally drained (closed) basins that are locally important but non-contributing to river systems that drain the prairies, OR forms in internally drained (closed) basins that are locally important but non-contributing to river systems that drain the prairies, OR drains directly to small prairie rivers (Battle, Souris, Assiniboine) >80% of runoff during snowmelt period drains directly to small prairie rivers (Battle, Souris, Assiniboine) >80% of runoff during snowmelt period Redistribution of snow to wetlands and stream channels in winter is critical to formation of runoff contributing area Redistribution of snow to wetlands and stream channels in winter is critical to formation of runoff contributing area Drainage of small streams and wetlands ceases completely in summer when actual evaporation* consumes most available water. Drainage of small streams and wetlands ceases completely in summer when actual evaporation* consumes most available water. Baseflow from groundwater often nonexistent. Baseflow from groundwater often nonexistent. Prairie streams are almost completely ungauged and often altered by dams, drainage, water transfers, etc Prairie streams are almost completely ungauged and often altered by dams, drainage, water transfers, etc *evaporation used here as transpiration + evaporation + sublimation

3 Prairie Hydrological Cycle

4 Prairie Runoff Generation Snow Redistribution to Channels Spring melt and runoff Water Storage in Wetlands Dry non-contributing areas to runoff

5 Non-Contributing Areas to Streamflow a Prairie Characteristic

6 Prairie Hydrology – don’t blink Smith Creek, Saskatchewan Drainage area ~ 450 km 2 No baseflow from groundwater

7 Information Needed to Estimate Runoff Snow accumulation and redistribution Snow accumulation and redistribution Melt rate Melt rate Infiltration to frozen soils Infiltration to frozen soils Infiltration excess forms runoff Infiltration excess forms runoff >80% of all runoff is snowmelt runoff >80% of all runoff is snowmelt runoff

8 Blowing Snow: Transport, Sublimation and Redistribution of Snow Pomeroy and Gray, Wat Resour. Res. (1990) Pomeroy and Male, J Hydrol. (1992) Pomeroy, Gray and Male, J Hydrol. (1993) Pomeroy and Gray, NHRI Science Report No. 7 (1995)

9 Effect of Blowing Snow Sublimation on Prairie Snow Supply (losses, mm SWE) LocationStubble-fieldFallow-field Calgary Peace River Swift Current Prince Albert Regina Yorkton Portage Winnipeg Pomeroy and Gray, NHRI Science Report No. 7 (1995) hourly simulations

10 Distribution of Blowing Snow over Landscapes Blowing snow transport, and sublimation relocate snow across the landscape from sources to sinks depending on fetch, orientation and area. Source Sink Stubble Field GrasslandBrushTrees Fallow Field

11 Shelterbelts on Prairies Winkler, Manitoba Conquest, Saskatchewan Transport to shelterbelts depends on upwind fetch and vegetation roughness

12 Spatially Distributed Snow Redistribution Snow mass balance equation St Denis, Saskatchewan

13 Results – Spatially distributed SWE Fang and Pomeroy, Hydrol Proc, in preparation

14 Spatially distributed SWE cont’

15

16

17

18

19

20

21

22 Spatial Pattern of Blowing Snow Sublimation

23 Simulations vs. Snow Surveys

24 Snowmelt Degree Day Method has problems in open environments with late melt, & in forests. Degree Day Method has problems in open environments with late melt, & in forests. Energy Balance snow CAN be estimated using reliable and readily applicable methods Energy Balance snow CAN be estimated using reliable and readily applicable methods

25 Coupled Mass and Energy Equations for Snowmelt MELT of SWE = Q M /(  w L f B i ) MELT of SWE = Q M /(  w L f B i ) Melt Energy Q M = Q* - Q E – Q H – Q G – dU/dt Melt Energy Q M = Q* - Q E – Q H – Q G – dU/dt Q* Net radiation (+ to snow surface) Q* Net radiation (+ to snow surface) Q E Evaporative energy (+ away from snow surface) Q E Evaporative energy (+ away from snow surface) Q H Sensible energy (+ away from snow surface) Q H Sensible energy (+ away from snow surface) Q G Ground heat flux (+ downward from snow) Q G Ground heat flux (+ downward from snow) dU/dt Internal energy change (+ loss from melt) dU/dt Internal energy change (+ loss from melt)

26 :004:008:0012:0016:0020:0024:00 Time Radiation (W/m²) Incoming SW Net SW Net Rad Net LW Diurnal Variation in Radiative Fluxes - clear day near Saskatoon

27 Empirical atmospheric transmittance equations Q si can be calculated directly if the atmospheric transmittence is known Q si can be calculated directly if the atmospheric transmittence is known Many similar relationships, all give similar results: Many similar relationships, all give similar results: Bristow and Campbell and Walter et al. Bristow and Campbell and Walter et al. Annandale Annandale All use a simple relationship between daily atmospheric transmittance and the range of daily air temperatures All use a simple relationship between daily atmospheric transmittance and the range of daily air temperatures

28 Edmonton

29 Snowpack Albedo Decay

30 CRHM Snowmelt Simulation

31 Infiltration to Frozen Soils Frozen soils can be permeable, but show reduced infiltration compared to unfrozen conditions Frozen soils can be permeable, but show reduced infiltration compared to unfrozen conditions ‘Frozen’ means a frost depth of at least 0.5 m ‘Frozen’ means a frost depth of at least 0.5 m Simple grouping of soil types Simple grouping of soil types Three classes of infiltrability: unlimited Inf=SWE restricted Inf=0 limitedInf = f(SWE, Saturation)

32 Snow Water Equivalent (mm) Restricted Unlimited :1 Gray’s Model of Infiltration into Frozen Soils - Prairie Environment Infiltration (mm) Saturation

33 Effect of Thawed Soils on Prairie Spring Runoff

34 Local Scale Prairie Runoff Because of frozen soils and rapidly melting snowcovers in the spring, 80% - 90% of prairie runoff is produced from snowmelt Because of frozen soils and rapidly melting snowcovers in the spring, 80% - 90% of prairie runoff is produced from snowmelt Snowmelt runoff is strongly controlled by snow drift location and size, soil moisture and mid winter thaws. Snowmelt runoff is strongly controlled by snow drift location and size, soil moisture and mid winter thaws. In wet years, there is often excess water to dryland cereal grain growing needs. In wet years, there is often excess water to dryland cereal grain growing needs. Hydrological computer simulations may tell us something about the reliability and behaviour of local prairie water supplies Hydrological computer simulations may tell us something about the reliability and behaviour of local prairie water supplies

35 Prairie hydrological modelling requires consideration of the following: Prairie hydrological modelling requires consideration of the following: Cold Regions Hydrological Model 1.Transport of water in liquid, vapour and frozen states (runoff, percolation, evaporation, sublimation, blowing snow); 2. Coupled mass and energy balances; 3. Phase change in snow & soils (snowmelt, infiltration in frozen soils, soil freezing and thawing); 4. Snow and rain interception in forest canopies; 5.Episodic flow between soil moisture, groundwater, ponds and streams. 6.Variable storage, drainage and contributing area 7.Land use change

36 CRHM Module Development Data from multiple sites Data from multiple sites Interpolation to the HRUs Interpolation to the HRUs Infiltration into soils (frozen and unfrozen) Infiltration into soils (frozen and unfrozen) Snowmelt (prairie & forest) Snowmelt (prairie & forest) Radiation – level, slopes Radiation – level, slopes Evapotranspiration Evapotranspiration Snow transport Snow transport Interception (snow & rain) Interception (snow & rain) Sublimation (dynamic & static) Sublimation (dynamic & static) Soil moisture balance Soil moisture balance Sub-surface runoff Sub-surface runoff Routing (hillslope & channel) Routing (hillslope & channel) Advection Advection DATA ASSIMILATION SPATIAL PARAMETERS Basin and HRU parameters are set. (area, latitude, elevation, ground slope, aspect) Basin and HRU parameters are set. (area, latitude, elevation, ground slope, aspect) PROCESSES

37 Creighton Tributary, Bad Lake as a typical Prairie Basin Moderately well drained plateau of grains and fallow drains into a coulee Semi-arid to sub-humid climate Typical drainage and landcover for much of southern prairies

38 Snowmelt Runoff over Frozen Soils Bad Lake: Semi-arid SW Saskatchewan Soil moisture is FALL soil moisture Snowmelt runoff is Spring Physically based Infiltration equations (Zhao & Gray, 1999) Cold Regions Hydrological Model

39 Bad Lake – Creighton Tributary Water Balance With 30% Summer Fallow Pomeroy, De Boer, Martz (2007)

40 Changed to Continuous Grain Cropping

41 Prairie Streamflow & Climate Change “first more, then less” Three most “reliable” climate change scenarios for hydrology suggest increases in annual prairie winter temperature and precipitation from the average: Three most “reliable” climate change scenarios for hydrology suggest increases in annual prairie winter temperature and precipitation from the average: ºC and +11% ºC and +11% ºC and +15.5% ºC and +15.5% Using these scenarios in the virtual upland basin results in a 24% rise in 2050 spring runoff, but a 37% drop by 2080, compared to conditions in the mid 1970s. Using these scenarios in the virtual upland basin results in a 24% rise in 2050 spring runoff, but a 37% drop by 2080, compared to conditions in the mid 1970s.

42 Prairie Climate Change – Winter Snow

43 Prairie Climate Change – Spring Runoff

44 Conclusions Prairie hydrological processes that control water balance and runoff generation have been largely quantified and described and model requirements are known, but have not been widely implemented in models. Prairie hydrological processes that control water balance and runoff generation have been largely quantified and described and model requirements are known, but have not been widely implemented in models. Major unknowns are the changing contributing area and its interaction with surface storage terms in poorly defined drainages. Major unknowns are the changing contributing area and its interaction with surface storage terms in poorly defined drainages.


Download ppt "Canadian Prairie Hydrology and Runoff Generation John Pomeroy Centre for Hydrology, University of Saskatchewan, Saskatoon www.usask.ca/hydrology."

Similar presentations


Ads by Google