Annual Freeze/Thaw Temperature Cycles in Soils on the Canadian Boreal Plain Comparison of SWAT Predictions to Measured Data

Transcription

1 Annual Freeze/Thaw Temperature Cycles in Soils on the Canadian Boreal Plain Comparison of SWAT Predictions to Measured Data Josiane A. Bélanger, Lakehead University Gordon Putz, University of Saskatchewan Brett M. Watson, University of Saskatchewan Ellie E. Prepas, Lakehead University & University of Alberta

2 Forest Watershed and Riparian Disturbance (FORWARD) Project Collaborative effort by: Researchers Forest-related industries First Nations Canadian public sectors FORWARD objectives are to adapt hydrological and water quality models to predict the effects of watershed disturbance, for application in forest management planning.

3 Objectives Test the SWAT soil temperature (ST) submodel for fine-grained soils in the cold region of the Boreal Plain. If required, modify the SWAT ST submodel.

4 Study Site

5 Vegetation wetland harvested deciduous burned conifer

6 2 m Vertical Profile Air Temperature Additional measurements include: Solar radiation Precipitation Vegetation biomass Soil bulk density 0.1 m 0.5 m Soil Temperature 1 m 0 m Soil Surface 0.1 m 0.5 m Soil Moisture 1 m

7 Soil Temperature Submodel Calculates ST at a specific depth from air temperature on the current day and ST on the previous day: soil ( z d ) = λ T ( z, d ) + ( ) { df ( T T ) T } 1 λ T +, n soil n 1 where λ is a lag factor AAir ssurf T soil (z,d n-1 ) is ST on previous day for a given depth (z) df is a depth factor T AAir is the long-term mean annual air temperature T ssurf is the soil surface temperature ssurf

8 Soil Temperature Submodel (cont d) Utilizes multiple input parameters from three categories: Soil Vegetation Climate

9 Original SWAT versus Observed ST 25 Observed Soil Temp r 2 = 0.83 Soil Temperature ( o C) o C 4.8 o C Original SWAT MAE = 3.0 RMSE = Nov-05 1-May-06 1-Nov-06 1-May-07 1-Nov-07 1-May-08 1-Nov-08 Date Conifer Site at 0.1 m Depth

10 Original SWAT versus Observed ST 25 Observed Soil Temp r 2 = 0.83 Soil Temperature ( o C) Original SWAT MAE = 3.0 RMSE = Nov-05 1-May-06 1-Nov-06 1-May-07 1-Nov-07 1-May-08 1-Nov-08 Date Conifer Site at 0.1 m Depth

11 Original SWAT versus Observed ST 25 Observed Soil Temp r 2 = 0.83 Soil Temperature ( o C) Original SWAT MAE = 3.0 RMSE = Nov-05 1-May-06 1-Nov-06 1-May-07 1-Nov-07 1-May-08 1-Nov-08 Date Conifer Site at 0.1 m Depth

12 Possible Reasons for Differences Spring and Summer Vegetation Solar radiation Autumn Vegetation Winter Snow

13 Model Testing Sensitivity analysis was conducted by varying the following parameters: Aboveground vegetation biomass and residue Depth of the soil profile Bulk density Lag coefficient Snow equation coefficients Original SWAT (default parameter values) and modified SWAT (varied parameter values) ST submodels were run for each site at 0.1, 0.5 and 1.0 m for each treatment type.

14 Modifications to ST Submodel Snow albedo (default = 0.8) was decreased: 0.66 for burned and harvested sites 0.43 for conifer, deciduous and wetlands sites Lag coefficient, λ, was increased

15 Sensitivity Analysis for Lag Coefficient 20 Soil Temperature ( o C) Observed λ = 0.70 λ = 0.80 λ = 0.96 λ = 0.97 λ = Nov-05 1-May-06 1-Nov-06 1-May-07 1-Nov-07 1-May-08 1-Nov-08 Date Conifer Site at 0.5 m Depth

16 Soil Temperature ( o C) Original and Modified SWAT versus Observed ST 20 Observed Soil Temp Original SWAT Modified SWAT Original SWAT r 2 = 0.77 MAE = 3.7 RMSE = 4.1 Modified SWAT r 2 = 0.96 MAE = 1.9 RMSE = Aug-06 1-Feb-07 1-Aug-07 1-Feb-08 1-Aug-08 Date Burned Site at 0.5 m Depth

17 Soil Temperature ( o C) Original and Modified SWAT versus Observed ST 20 Observed Soil Temp Original SWAT 15 Modified SWAT Original SWAT r 2 = 0.66 MAE = 2.3 RMSE = 2.8 Modified SWAT r 2 = 0.96 MAE = 0.7 RMSE = Jul-06 1-Jan-07 1-Jul-07 1-Jan-08 1-Jul-08 1-Jan-09 Date Wetland Site at 0.5 m Depth

18 Soil Temperature ( o C) Original and Modified SWAT versus Observed ST 20 Observed Soil Temp Original SWAT 15 Modified SWAT Original SWAT r 2 = 0.70 MAE = 2.6 RMSE = 3.1 Modified SWAT r 2 = 0.90 MAE = 1.3 RMSE = Nov-05 1-May-06 1-Nov-06 1-May-07 1-Nov-07 1-May-08 1-Nov-08 Date Conifer Site at 0.5 m Depth

19 Discussion Model efficiency was increased for all depths and treatments by increasing the lag coefficient Maximum soil temperature differences in summer and winter were reduced

20 Snow Insulation Equation Determines the insulation provided by vegetation or snow: bcv max CV + exp 4 CV SNO, ( ) CV SNO + exp( A B SNO) = where bcv is the insulation parameter CV is the above ground biomass and residue in kg ha -1 SNO is the snow depth in mmh 2 O Parameters: A = B =

21 Sensitivity Analysis for Snow Equation Parameter A 5 4 Soil Temperature ( o C) Observed A = 0 A = 0,1 A = 1,0 A = 10 A = 6, Nov-05 1-May-06 1-Nov-06 1-May-07 1-Nov-07 1-May-08 1-Nov-08 Conifer Site at 0.5 m Depth Date

22 Sensitivity Analysis for Snow Equation Parameter B 5 4 Soil Temperature ( o C) Observed -2 B = 0 B = 0,01-3 B = 0,1-4 B = 1-5 B = 0, Nov-05 1-May-06 1-Nov-06 1-May-07 1-Nov-07 1-May-08 1-Nov-08 Conifer Site at 0.5 m Depth Date

23 Conclusions The modified SWAT was able to effectively model ST in the spring, summer and autumn seasons on the Boreal Plain. Insulation by a deep snowpack is not reflected in the SWAT model. To simulate ST in winter months for northern climates, further modifications to the model must account for deep and persistent snowpacks.

24 Acknowledgements Millar Western Forest Products Ltd. and the Natural Sciences and Engineering Research Council of Canada (NSERC) for funding this research. Past and present members of FORWARD: Janice Burke Nicole Fraser Steve Nadworny Dr. Douglas MacDonald Mark Serediak Dr. Ivan Whitson The FORWARD project is funded by: NSERC Collaborative Research and Development Program Millar Western Forest Products Ltd. Blue Ridge Lumber Inc. (a division of West Fraser Timber Company Ltd.) Alberta Newsprint Company (ANC Timber) Vanderwell Contractors (1971) Ltd. Abitibi Bowater Inc. Buchanan Forest Products Ltd. Buchanan Lumber (a division of Gordon Buchanan Enterprises) Talisman Energy Inc. TriStar Oil & Gas Ltd. Canada Foundation for Innovation Alberta Forestry Research Institute Forest Resource Improvement Association of Alberta FedNor Ontario Innovation Trust Living Legacy Research Program