Q S WINDWARD, BARE GROUND, CLASS with blowing snow ... · Blowing snow sublimation and transport...
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0 0.1 0.2 0.3 0.4 0.5 0.6 Snow depth (m) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 14-Oct-08 14-Nov-08 14-Dec-08 14-Jan-09 14-Feb-09 14-Mar-09 14-Apr-09 14-May-09 Snow depth (m) CLASS with blowing snow algorithms: tests over alpine terrain Matthew K. MacDonald, John W. Pomeroy and Alain Pietroniro Centre for Hydrology, University of Saskatchewan, 117 Science Place, Saskatoon, Saskatchewan, Canada, S7N 5C8 Background Snowcover over complex terrain is highly variable due to blowing snow redistribution Field observations and modelling difficulties offer strong evidence that accounting for blowing snow transport and sublimation is necessary to simulate snowcover depletion and runoff in windswept terrain. The current versions of CLASS and MESH do not include blowing snow sublimation, transport and redistribution algorithms. Scope and Objectives Blowing snow sublimation and transport algorithms from the Prairie Blowing Snow Model (PBSM) were incorporated in the Canadian Land Surface Scheme (CLASS) version 3.4. Point simulation of snow depth using CLASS without and with blowing algorithms (CLASS and CLASS-PBSM, respectively) were compared to snow depth measurements. The next step is to produce distributed snowcover simulations over mountainous terrain (i.e. over multiple landscape units). Study Site Location: 50º 57' N, 115º 10' W Mean Elevation: 2310 m ASL Mean Annual Precipitation: 900 mm (60-75% snow) Mean Temperatures: -8 to -5 o C (September-April) Fisera Ridge, Marmot Creek Basin, Kananaskis Country, Alberta PBSM algorithms (Pomeroy et al., 1993; Pomeroy and Li, 2000) were coded into the water budget calculation routine (CLASSW). Blowing sublimation and transport calculations were performed for two of the four CLASS subareas: snow-covered ground and canopy over snow. PBSM calculations were separated into three subroutines. Discussion Acknowledgements Financial support provided through the IP3 Network funded by CFCAS. Diana Verseghy, Paul Bartlett and Frank Seglenieks assisted with CLASS model coding and parameterization. Conclusions CLASS simulations over windswept terrain are significantly improved when including physically- based blowing snow sublimation and transport calculations. Difficulties remain in simulating snowmelt in this environment. Snow transport may be underestimated due to overestimated melt. A framework now exists within MESH to distribute blowing snow transport amongst multiple landscape units. This inter-tile transport framework can be generalized for other hydrological fluxes (e.g. overland flow). Landcover: 25% needleleaf shrubs, 25% grass, 50% bare ground/rocks Model Structure Data Three years of simulations: 2006/2007, 2007/2008, 2008/2009 Meteorological and sonic now depth data was obtained from a hilltop station located on Fisera Ridge. Precipitation data was obtained from a GEONOR precipitation gauge at 1845 m ASL (2006/2007 and 2007/2008) and at Fisera Ridge (only 2008/2009). Model runs were initialized using soil temperature measurements made at 1845 m ASL Framework for inter-tile snow redistribution CLASS-PBSM provided significantly better simulated snow depth than CLASS. CLASS and CLASS-PBSM were calibrated using the Dynamically Dimensioned Search algorithm (DDS; Tolson and Shoemaker, 2007) to SR50 sonic snow depth measurements for 2007/2008 and validated for the other years. CLASS parameters calibrated: vegetation albedo, roughness length, minimum and maximum LAI, and D100 limiting snow depth Additional PBSM parameters calibrated: vegetation height and density Modelling Strategy Results CLASSW PBSMrun CLASSW Probability Threshold No Yes Flux Calculations Snow removed from pack PBSMrun: calls subroutines & calculates changes to snowpack ProbabilityThreshold: calculates probability of blowing snow occurrence based on meteorology (Li & Pomeroy, 1997) FluxCalculations: calculates snow transport & sublimation rates Thermodynamic feedback due to blowing snow sublimation is addressed empirically in PBSM vertical atmospheric profiles. No changes were made to surface energy balance calculations (CLASST) at this stage. Difficulties remain with rapid snowmelt, particularly during late winter and spring. Year RMSE (cm) MB CLASS CLASS-PBSM CLASS CLASS-PBSM 2006/2007 20.2 7.7 1.82 -0.43 2007/2008 26.1 5.4 4.03 -0.14 2008/2009 35.8 19.2 0.86 -0.37 2007/2008 (calibration) Observed CLASS CLASS-PBSM There is now a framework within MESH to redistribute snow transport amongst multiple landscape units with a grid square. The inter-tile snow redistribution parameterization requires one parameter per landscape unit. Snow redistribution factor: percent of aggregated calculated snow transport that is to be deposited within a given landscape unit. 2008/2009 (validation) MESH_driver: calls all MESH routines including data reading, CLASS and hydrologic routing CLASSZZ: performs energy & water balance checks Redistrib_Snow: redistributes blowing snow mass, calculates changes to snowpack properties MESH_driver Redistrib_Snow MESH_driver Remove “vanishingly small” snowpack & recalculate snowpack properties CLASSZZ CLASSZZ Q S Q S Q T Q T TOPOGRAPHIC DEPRESSION WINDWARD LEEWARD GRASS FOREST BARE GROUND SHRUB Q S Q T WINDWARD, BARE GROUND, GRASS LEEWARD, FOREST SHRUB, DEPRESSION BLOWING SNOW BLOWING SNOW BLOWING SNOW IF CAPACITY/THRESHOLD IS EXCEEDED Q S Q S Q T Q T TOPOGRAPHIC DEPRESSION WINDWARD LEEWARD GRASS FOREST BARE GROUND SHRUB Q S Q T Q S Q S Q T Q T TOPOGRAPHIC DEPRESSION WINDWARD LEEWARD GRASS FOREST BARE GROUND SHRUB Q S Q T WINDWARD, BARE GROUND, GRASS LEEWARD, FOREST SHRUB, DEPRESSION WINDWARD, BARE GROUND, GRASS LEEWARD, FOREST SHRUB, DEPRESSION BLOWING SNOW BLOWING SNOW BLOWING SNOW BLOWING SNOW BLOWING SNOW BLOWING SNOW IF CAPACITY/THRESHOLD IS EXCEEDED This redistribution factor algorithm can be generalized and applied to other hydrological fluxes (e.g. overland flow between landscape units). 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 Snow depth (m) 2006/2007 (validation) Year Snow transport (mm) Blowing snow sublimation (mm) 2006/2007 17.8 67.4 2007/2008 35.4 117.1 2008/2009 38.6 208.0
Transcript of Q S WINDWARD, BARE GROUND, CLASS with blowing snow ... · Blowing snow sublimation and transport...
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CLASS with blowing snow algorithms: tests over alpine terrain
Matthew K. MacDonald, John W. Pomeroy and Alain PietroniroCentre for Hydrology, University of Saskatchewan,
117 Science Place, Saskatoon, Saskatchewan, Canada, S7N 5C8
Background
Snowcover over complex terrain is highly variable due to blowing snow redistribution
Field observations and modelling difficulties offer strong evidence that accounting for blowing snow
transport and sublimation is necessary to simulate snowcover depletion and runoff in windswept
terrain.
The current versions of CLASS and MESH do not include blowing snow sublimation, transport and
redistribution algorithms.
Scope and Objectives
Blowing snow sublimation and transport algorithms from the Prairie Blowing Snow Model (PBSM)
were incorporated in the Canadian Land Surface Scheme (CLASS) version 3.4.
Point simulation of snow depth using CLASS without and with blowing algorithms (CLASS and
CLASS-PBSM, respectively) were compared to snow depth measurements.
The next step is to produce distributed snowcover simulations over mountainous terrain (i.e. over
multiple landscape units).
Study Site
Location:
50º 57' N, 115º 10' W
Mean Elevation:
2310 m ASL
Mean Annual Precipitation:
900 mm (60-75% snow)
Mean Temperatures:
-8 to -5 oC
(September-April)
Fisera Ridge, Marmot Creek Basin, Kananaskis Country, Alberta
PBSM algorithms (Pomeroy et al., 1993; Pomeroy and Li, 2000) were coded into the water budget
calculation routine (CLASSW).
Blowing sublimation and transport calculations were performed for two of the four CLASS
subareas: snow-covered ground and canopy over snow.
PBSM calculations were separated into three subroutines.
Discussion
Acknowledgements
Financial support provided through the IP3 Network funded by CFCAS. Diana Verseghy, Paul
Bartlett and Frank Seglenieks assisted with CLASS model coding and parameterization.
Conclusions
CLASS simulations over windswept terrain are significantly improved when including physically-
based blowing snow sublimation and transport calculations.
Difficulties remain in simulating snowmelt in this environment. Snow transport may be
underestimated due to overestimated melt.
A framework now exists within MESH to distribute blowing snow transport amongst multiple
landscape units. This inter-tile transport framework can be generalized for other hydrological fluxes
(e.g. overland flow).
Landcover: 25% needleleaf shrubs, 25% grass, 50% bare ground/rocks
Model Structure
Data
Three years of simulations: 2006/2007, 2007/2008, 2008/2009
Meteorological and sonic now depth data was obtained from a hilltop station located on Fisera Ridge.
Precipitation data was obtained from a GEONOR precipitation gauge at 1845 m ASL (2006/2007 and
2007/2008) and at Fisera Ridge (only 2008/2009).
Model runs were initialized using soil temperature measurements made at 1845 m ASL
Framework for inter-tile snow redistribution
CLASS-PBSM provided significantly better simulated snow depth than CLASS.
CLASS and CLASS-PBSM were calibrated using the Dynamically Dimensioned Search algorithm
(DDS; Tolson and Shoemaker, 2007) to SR50 sonic snow depth measurements for 2007/2008 and
validated for the other years.
CLASS parameters calibrated: vegetation albedo, roughness length, minimum and maximum LAI,
and D100 limiting snow depth
Additional PBSM parameters calibrated: vegetation height and density
Modelling Strategy
Results
CLASSW
PBSMrun
CLASSW
Probability
Threshold
No
YesFlux
Calculations
Snow
removed
from pack
PBSMrun: calls subroutines & calculates changes to snowpack
ProbabilityThreshold: calculates probability of blowing snow occurrence
based on meteorology (Li & Pomeroy, 1997)
FluxCalculations: calculates snow transport & sublimation rates
Thermodynamic feedback due to
blowing snow sublimation is addressed
empirically in PBSM vertical atmospheric
profiles.
No changes were made to surface
energy balance calculations (CLASST)
at this stage. Difficulties remain with rapid snowmelt, particularly during late winter and spring.
Year RMSE (cm) MB
CLASS CLASS-PBSM CLASS CLASS-PBSM
2006/2007 20.2 7.7 1.82 -0.43
2007/2008 26.1 5.4 4.03 -0.14
2008/2009 35.8 19.2 0.86 -0.37
2007/2008 (calibration)
Observed CLASS CLASS-PBSM
There is now a framework within MESH to redistribute snow transport amongst multiple landscape
units with a grid square.
The inter-tile snow redistribution parameterization requires one parameter per landscape unit.
Snow redistribution factor: percent of aggregated calculated snow transport that is to be
deposited within a given landscape unit.
2008/2009
(validation)
MESH_driver: calls all MESH routines including data reading,
CLASS and hydrologic routing
CLASSZZ: performs energy & water balance checks
Redistrib_Snow: redistributes blowing snow mass, calculates
changes to snowpack properties
MESH_driver
Redistrib_Snow
MESH_driver
Remove “vanishingly
small” snowpack &
recalculate snowpack
properties
CLASSZZ
CLASSZZ
QS
QS
QT
QT
TOPOGRAPHICDEPRESSION
WINDWARD
LEEWARD
GRASS FORESTBAREGROUND
SHRUB
QS
QT
WINDWARD,BARE GROUND,
GRASS
LEEWARD,FOREST
SHRUB,DEPRESSIONBLOWING SNOW
BLO
WIN
G S
NOW
BLO
WIN
G S
NOW
IF CAPACITY/THRESHOLDIS EXCEEDED
QS
QS
QT
QT
TOPOGRAPHICDEPRESSION
WINDWARD
LEEWARD
GRASS FORESTBAREGROUND
SHRUB
QS
QT
QS
QS
QT
QT
TOPOGRAPHICDEPRESSION
WINDWARD
LEEWARD
GRASS FORESTBAREGROUND
SHRUB
QS
QT
WINDWARD,BARE GROUND,
GRASS
LEEWARD,FOREST
SHRUB,DEPRESSION
WINDWARD,BARE GROUND,
GRASS
LEEWARD,FOREST
SHRUB,DEPRESSIONBLOWING SNOW
BLO
WIN
G S
NOW
BLO
WIN
G S
NOW
BLOWING SNOW
BLO
WIN
G S
NOW
BLO
WIN
G S
NOW
IF CAPACITY/THRESHOLDIS EXCEEDED
This redistribution factor algorithm can be generalized and applied to other hydrological fluxes (e.g.
overland flow between landscape units).
00.050.10.150.20.250.30.350.40.450.5
Sn
ow
de
pth
(m
) 2006/2007 (validation)
Year Snow transport (mm) Blowing snow sublimation (mm)
2006/2007 17.8 67.4
2007/2008 35.4 117.1
2008/2009 38.6 208.0
