Headwaters Hydrology: Principles to Policy John Pomeroy Canada Research Chair in Water Resources and...
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Transcript of Headwaters Hydrology: Principles to Policy John Pomeroy Canada Research Chair in Water Resources and...
Headwaters Hydrology: Headwaters Hydrology: Principles to PolicyPrinciples to Policy
John PomeroyJohn Pomeroy Canada Research Chair in Water Resources and Climate ChangeCanada Research Chair in Water Resources and Climate Change
Centre for HydrologyCentre for HydrologyUniversity of Saskatchewan, SaskatoonUniversity of Saskatchewan, Saskatoon
Purpose of TalkPurpose of Talk Outline the hydrological principles governing Outline the hydrological principles governing
water cycling and streamflow generation in water cycling and streamflow generation in mountain headwater basinsmountain headwater basins
Investigate the impacts on hydrological cycling Investigate the impacts on hydrological cycling of changing forest cover and climateof changing forest cover and climate
Note the challenges to preserving the Note the challenges to preserving the hydrological cycle in this regionhydrological cycle in this region
Outline some management practices to meet Outline some management practices to meet current and anticipated challenges in the current and anticipated challenges in the RockiesRockies
Suggest some policy optionsSuggest some policy options
Canadian Canadian Rockies are Rockies are
the the Hydrological Hydrological
Apex of Apex of North North
AmericaAmerica
Rocky Mountains Headwaters: Rocky Mountains Headwaters: Source of the Saskatchewan-NelsonSource of the Saskatchewan-Nelson
Saskatchewan, where it heads (if it can)Saskatchewan, where it heads (if it can)
Hudson Bay Hudson Bay (where it controls sea ice, ocean salinity (where it controls sea ice, ocean salinity and the global climate system)and the global climate system)
Cold Regions Hydrological Cycle Cold Regions Hydrological Cycle
InterflowInterflow
RunoffRunoff
SnowfallSublimation
Blowing Snow Evaporation EvaporationRainfall
Snowmelt
Infiltration to Frozen Ground
Groundwater FlowGroundwater Flow
Precipitation
Ice
Lakes
0
50
100
150
3/2 4/1 5/1 6/1 7/1 8/1 8/31 9/30 10/31 11/30
Flo
w r
ate
(m
3 /s)
snowmelt in mountains
Rocky Mountain Runoff is Mostly Rocky Mountain Runoff is Mostly Snowmelt Snowmelt
Surface Runoff
Groundwater Discharge
How Much Snow is There?How Much Snow is There?
Less and Less…..Less and Less…..US NOAA satellite US NOAA satellite measured average measured average change (days/yr) change (days/yr) in snow cover in snow cover duration (Feb.-Jul.) duration (Feb.-Jul.) over the period over the period 1972-2000. 1972-2000.
Rockies: 1 to 2 Rockies: 1 to 2 month decrease! month decrease!
Marmot Creek Research BasinMarmot Creek Research Basin 1450-2886 m.a.s.l. Kananaskis Valley, Bow River1450-2886 m.a.s.l. Kananaskis Valley, Bow River AlpineAlpine SubalpineSubalpine MontaneMontane ClearcutClearcut MeadowMeadow +600 mm+600 mm
precipitationprecipitation 70% snowfall70% snowfall ~50% runoff~50% runoff
Marmot Basin
Bow River valley
Kananaskis River valley
Airborne Airborne LiDAR LiDAR Snow DepthSnow Depth
LiDAR flights in
Aug 2007 & March 2008
Differencing of images after
correction provides depth
and basis for runoff estimates
First detailed map of
snow depth distribution
in the Rockies!
Hopkinson & Pomeroy
Snow Regimes Snow Regimes Forest Snow – Open SnowForest Snow – Open Snow
Snow Accumulation VariabilitySnow Accumulation Variability
Blowing Snow in MountainsBlowing Snow in Mountains
Inter-basin water transfer
Transport of snowto deep drifts
Supports glaciers,late lying snowfields,contributing areas
Water supply to sub-alpine forests
Melt controls summerstreamflow
Blowing Snow Entering BasinBlowing Snow Entering Basin
Alpine Tundra Ridgetop – most Alpine Tundra Ridgetop – most snowfall eroded by blowing snowsnowfall eroded by blowing snow
0
20
40
60
80
100
120
140
160
180
23-Sep 23-Oct 22-Nov 22-Dec 21-Jan 20-Feb 22-Mar 21-Apr 21-May
Sn
ow
Wa
ter
Eq
uiv
ale
nt
(mm
)
Snow Accumulation
Snowfall
Blowing Snow Transport Over Complex Blowing Snow Transport Over Complex TerrainTerrain
QSUBLIM
QSUBLIM
QTRANSP
QTRANSP
TOPOGRAPHICDEPRESSION
WINDWARD HILL
LEEWARDHILL
GRASS FORESTBAREGROUND
SHRUB
QSUBLIM
QTRANSP
WINDWARD HILL,BARE GROUND,
GRASS
LEEWARD HILL,FOREST
SHRUB,DEPRESSIONBLOWING SNOW
BLOW
ING
SNO
W
BLOW
ING
SN
OW
IF CAPACITY/THRESHOLDIS EXCEEDED
MacDonald, Pomeroy, Pietroniro
0 500 1000 1500 2000 2500 30000
500
1000
1500
2000
2500
3000
0 500 1000 1500 2000 2500 30000
500
1000
1500
2000
2500
3000
Linear simulation of westerly flow over Mountain Ridge and Valley
Windspeed Wind Direction
3 kmGridded Wind Flow Model Coupled to Blowing Snow Model
Essery and Pomeroy
3 km
Simulation of Hillslope Snowdrift
Gridded Blowing Snow Model Resulting Drifts
Essery & Pomeroy
Glacier Retreat in the Columbia IcefieldsGlacier Retreat in the Columbia Icefields
Mapped fromNASA LANDSATsatellite
Glaciers are fed byalpine snow, esp.wind drifted snow
36% loss of glaciatedarea of South Sask Basin 1975-1998
Demuth & Pietroniro
Alpine Snow ChallengesAlpine Snow Challenges Seldom monitored – valley bottom snow stations are not Seldom monitored – valley bottom snow stations are not
good indicators for the alpine, sparse snow surveysgood indicators for the alpine, sparse snow surveys 1 Environment Canada weather station in alpine zone1 Environment Canada weather station in alpine zone Observed glacier decline is associated with reduced Observed glacier decline is associated with reduced
alpine snow accumulationalpine snow accumulation Inadequate understanding of alpine snow dynamicsInadequate understanding of alpine snow dynamics Not incorporated in most climate and hydrology modelsNot incorporated in most climate and hydrology models Impacts of Climate Change?Impacts of Climate Change?
Warmer winters and more lush alpine vegetation reduce blowing Warmer winters and more lush alpine vegetation reduce blowing snow redistributionsnow redistribution
Less snow redistributed to glaciersLess snow redistributed to glaciers More snow at high elevation and less at treelineMore snow at high elevation and less at treeline
Stronger Chinooks increase sublimation lossStronger Chinooks increase sublimation loss Less snow on windward slopes and in cornicesLess snow on windward slopes and in cornices
Intercepted Snow in ForestsIntercepted Snow in Forests Snow intercepted in Snow intercepted in
canopies for weeks in canopies for weeks in cold periodscold periods
Snow does not blow Snow does not blow from forest canopies from forest canopies to clearings in any to clearings in any significant quantitiessignificant quantities
Intercepted snow is Intercepted snow is well exposed to well exposed to sunlight and dry sunlight and dry windswinds
Interception Efficiency = Interception Efficiency = interception/snowfall (I/P)interception/snowfall (I/P)
0
0.2
0.4
0.6
0.8
1
0 2 4 6
LAI
I/P
T= -1.0 °CT= -5.0 °CT= -30.0 °C
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20 25 30P (mm SWE)
I/P
Lo = 1.0 mm SWELo = 3.0 mm SWELo = 5.0 mm SWE
More snow is trapped by denser forests
Snow is trapped moreefficiently from lightsnowfalls
spruce
pineburned
Hedstrom and Pomeroy
Intercepted Snow SublimationIntercepted Snow Sublimation
Thermal Infrared Image
Intercepted snow is cool
Snow Interception & Sublimation Snow Interception & Sublimation Loss in Marmot Creek Loss in Marmot Creek
0
20
40
60
80
100
120
140
North South East West
Sno
w W
ater
Equ
ival
ent m
m
Forest
Clearing
MacDonald & Pomeroy
Interception & Sublimation of Snow Interception & Sublimation of Snow on a Weighed Hanging Treeon a Weighed Hanging Tree
0
0.5
1
1.5
2
2.5
3
3.5
4
38 42 46 50 54 58 62 66 70 74 78 82Julian Day
Inte
rcep
ted
snow
load
(mm
) .
-39-36-33-30-27-24-21-18-15-12-9-6-303691215
Air
Tem
pera
ture
(C)
.
snow load air temp
Effect of Forest Removal on Snow Effect of Forest Removal on Snow AccumulationAccumulation
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 1 2 3 4 5Leaf Area Index
Sn
ow
in
Fo
rest
/ S
no
w i
n C
lear
ing
Measured
Parametric Model
Sparsely Wooded
Medium Density, Young
Dense Mature Canopy
Deforestation Effect
Snow Interception and Sublimation Snow Interception and Sublimation in Rocky Mountain Forestsin Rocky Mountain Forests
Intercepted snow sublimation loss up to 60% of Intercepted snow sublimation loss up to 60% of seasonal snowfall in the Rockies seasonal snowfall in the Rockies
Any disturbance that reduces coniferous canopy Any disturbance that reduces coniferous canopy cover will increase snow accumulation cover will increase snow accumulation
Climate and Forest Change Impacts?Climate and Forest Change Impacts? Reduction in forest cover due to pine beetle, fire, Reduction in forest cover due to pine beetle, fire,
clearing will dramatically reduce sublimation lossesclearing will dramatically reduce sublimation losses Needle removal with standing deadwood will more than Needle removal with standing deadwood will more than
double snow accumulationdouble snow accumulation Sublimation losses insensitive to temperatureSublimation losses insensitive to temperature
SnowmeltSnowmelt
Incoming solar Incoming solar and thermal and thermal radiation radiation
Warm air Warm air massesmasses
Energy storageEnergy storage Terrain and Terrain and
vegetation vegetation effectseffects
Snow EnergeticsSnow Energetics
Alpine Snowmelt: Solar Radiation & Alpine Snowmelt: Solar Radiation & Convective Heat Transfer Convective Heat Transfer
-20
0
20
40
60
80
100
120
Mean Energy
(W/m2)
ValleyBottom
South Face North Face
Melt + InternalNet RadiationGround HeatSensible HeatLatent Heat
20o slopesSouth Face
North FaceValley Bottom
Solution: landscape units
May 8, 2007
Jul 4, 2007
Jun 2, 2007
Cirque SCA fraction
0.95
0.62
0.08
08-May
02-Jun
04-Jul
De Beer & Pomeroy
Snowcover Depletion in Alpine Basins
0
0.25
0.5
0.75
1
Date
SCA
Fra
ctio
n
MeasuredSCD curve
ModeledSCD curve
0
0.25
0.5
0.75
1
Date
SC
A F
ract
ion
MeasuredSCD curve
ModeledSCD curve
North Face
South Face
Lidar and canopy delineation Shadow simulation
Sub-alpine Solar & Thermal Radiation for Snowmelt
Essery
•Patchy forest means that traditional estimation techniques will not work•Solar radiation greatly reduced under forest canopies and in shadows•Convective heat transfer in forests is controlled by canopy temperature
Sub-alpine Solar Radiation
Simulated skyview
0
100
200
300
400
500
600
84 85 86
Day (2003)
SW
(W
/m2)
Measured
Modelled
Simulated Solar Radiation forSnowmelt
Clear Overcast
Possible to estimate solar and thermal radiation even in patchy forests if LiDARinventories of forest structure are available Essery & Pomeroy
Hot Trees – Thermal RadiationHot Trees – Thermal Radiation
Thermal Radiation from PineThermal Radiation from Pine
150
170
190
210
230
250
270
290
310
330
350
74 74.5 75 75.5 76 76.5 77 77.5 78Julian Day
Exi
tan
ce W
/m²
Needles
Trunk
Sky
Air
Forest temperatures enhanced above air temperature by extinction of solar radiationThermal radiation from forests greatly enhances melt compared to open environments
Forest Density Impacts Forest Density Impacts Snowmelt EnergySnowmelt Energy
Clearing Mature Forest
Net radiation = solar + thermal radiationEllis &Pomeroy
Snowmelt Runoff Generally Increases Snowmelt Runoff Generally Increases with Decreasing Forest Coverwith Decreasing Forest Cover
0
10
20
30
40
50
60
Meltwater Runoff (mm)
1994 1995 1996
Pine
Mixed-wood
Plantation
Clear-cut
Low forest density associated with high soil moisture, deep snow and rapid melt
Snowmelt and RunoffSnowmelt and Runoff Snowmelt in Rockies is solar and thermal radiation Snowmelt in Rockies is solar and thermal radiation
driven in forests, with wind effects in alpine and clearingsdriven in forests, with wind effects in alpine and clearings Slope and aspect differencesSlope and aspect differences SensitiveSensitive to presence of vegetation cover to presence of vegetation cover Forest melt is Forest melt is insensitiveinsensitive to air temperature to air temperature Clearing/alpine melt is Clearing/alpine melt is sensitivesensitive to air temperature to air temperature
Forest clearing on south facing slopes and level sites Forest clearing on south facing slopes and level sites acceleratesaccelerates melt melt
Forest clearing on north facing slopes Forest clearing on north facing slopes deceleratesdecelerates melt melt Higher snow accumulation and melt rates from Higher snow accumulation and melt rates from forest forest
removal cause greater runoff quantitiesremoval cause greater runoff quantities in spring in spring
Hydrological Change in the Hydrological Change in the HeadwatersHeadwaters
Need continuous Need continuous research basin recordsresearch basin records Marmot Creek – the only long term research
basin in the Canadian Rocky MountainsIHD 1962-1987IP3 2005-2009
Reconstruction of temperature and streamflow
Temperature Trends at Elevation in Temperature Trends at Elevation in Marmot Creek, 1962-PresentMarmot Creek, 1962-Present
Winters are warmer by 3 to 4 oC since the 1960s
Harder & Pomeroy
Annual Precipitation in Kananaskis Annual Precipitation in Kananaskis
Cycling but no statistically significant trend, wetter since 1960s
Harder & Pomeroy
Rainfall versus Snowfall,Rainfall versus Snowfall,Kananaskis ValleyKananaskis Valley
Warmer winters = less snowfallWarmer winters = more rainfall
Temperature Change
Harder & Pomeroy
Cycling but No Trend in Timing of Peak Cycling but No Trend in Timing of Peak Streamflow from Marmot CreekStreamflow from Marmot Creek
Day of year of peak streamflow, Middle Creek
Harder & Pomeroy
Marmot Creek Spring Peak and Annual Marmot Creek Spring Peak and Annual Streamflow Decline of ~30% Since 1960sStreamflow Decline of ~30% Since 1960s
Middle Creek June Streamflow cubic metres/second
Harder & Pomeroy
Marmot Creek Climate Change Marmot Creek Climate Change Implications for Water PolicyImplications for Water Policy
Warmer winters Warmer winters Less snowfall, more rainfallLess snowfall, more rainfall Peak streamflows 30% smaller than 1960sPeak streamflows 30% smaller than 1960s Summer streamflows 29% smaller than 1960sSummer streamflows 29% smaller than 1960s No change in timing of peak streamflowNo change in timing of peak streamflow
Less mountain streamflow available for filling Less mountain streamflow available for filling reservoirs, irrigation, communities, ecosystem reservoirs, irrigation, communities, ecosystem needs, oceans, etc. needs, oceans, etc. Requires adaptation NOW.Requires adaptation NOW.
Careful, only one site – regional variation Careful, only one site – regional variation unknown.unknown.
Deforestation Deforestation
Forest Management?Forest Management? Possible to double snow accumulation through forest Possible to double snow accumulation through forest
thinning, partial clearing or permitting disease or firethinning, partial clearing or permitting disease or fire Possible to retain low snowmelt rate by retaining some Possible to retain low snowmelt rate by retaining some
canopy structure (thinning, standing deadwood, canopy structure (thinning, standing deadwood, shelterwood)shelterwood)
Careful!Careful! At Marmot direct impacts on annual streamflow At Marmot direct impacts on annual streamflow from cutting in early 1980s were difficult to measure. But from cutting in early 1980s were difficult to measure. But it works in the Upper Colorado…..it works in the Upper Colorado…..
Careful!Careful! Can contribute to flooding, erosion, ….. Can contribute to flooding, erosion, ….. Careful!Careful! Forest cover removal will increase sensitivity of Forest cover removal will increase sensitivity of
melt timing and rate to climate warmingmelt timing and rate to climate warming Careful!Careful! We have inadequate monitoring and predictive We have inadequate monitoring and predictive
capacity to prescribe this safely and with any reasonable capacity to prescribe this safely and with any reasonable confidenceconfidence
Science Policy ImplicationsScience Policy Implications Urgent to Urgent to
confirm hydrological response from forest manipulation trials confirm hydrological response from forest manipulation trials conducted in Marmot Creek in the 1980s. Streamflow conducted in Marmot Creek in the 1980s. Streamflow observations stopped in 1986.observations stopped in 1986.
examine hydrological response to forest change in main ranges examine hydrological response to forest change in main ranges as well as front rangesas well as front ranges
better quantify and understand changes to alpine snow and better quantify and understand changes to alpine snow and glacier hydrology from changing high altitude climateglacier hydrology from changing high altitude climate
Improve and test predictive models so that virtual simulations Improve and test predictive models so that virtual simulations can be conducted of coupled climate, glacier and forest changecan be conducted of coupled climate, glacier and forest change
Restoration of network of IHD Basins in the Rockies with Restoration of network of IHD Basins in the Rockies with site selection keyed to major policy uncertaintiessite selection keyed to major policy uncertainties
Enhancement of our networks that measure, monitor and Enhancement of our networks that measure, monitor and observe hydrology and meteorology in mountains observe hydrology and meteorology in mountains especially at high elevationsespecially at high elevations
How to Better Observe and Predict?How to Better Observe and Predict? Focussed Experiment Area to couple key issuesFocussed Experiment Area to couple key issues
Mountain snow and glacier dynamics (western cordillera)Mountain snow and glacier dynamics (western cordillera) Downstream drought and water supply (intermountain interior and northern Downstream drought and water supply (intermountain interior and northern
plains)plains) International WatersInternational Waters
Rocky Mountain Hydrometeorological ObservatoryRocky Mountain Hydrometeorological Observatory Coordinated, integrated observationsCoordinated, integrated observations
Surface water, groundwater, snow & iceSurface water, groundwater, snow & ice Remote sensingRemote sensing Research basinsResearch basins
Regional Data Assimilation & PredictionRegional Data Assimilation & Prediction Information PortalInformation Portal Information InterpretationInformation Interpretation
Emphasis on water security and climate change impactsEmphasis on water security and climate change impacts
Concluding RemarksConcluding Remarks Snowpacks and vegetation, play an important Snowpacks and vegetation, play an important
role in governing Rocky Mountain streamflowrole in governing Rocky Mountain streamflow Physically-based computer models are having Physically-based computer models are having
initial successes in estimating these effects for initial successes in estimating these effects for water resource predictionwater resource prediction
Climate change is reducing snowmelt and Climate change is reducing snowmelt and streamflow in headwater basinsstreamflow in headwater basins
Forest management might mitigate some of the Forest management might mitigate some of the streamflow reduction, but has risksstreamflow reduction, but has risks
BothBoth our observation and hydrological modelling our observation and hydrological modelling capacities will require further development to capacities will require further development to meet the emerging needs of Rocky Mountain meet the emerging needs of Rocky Mountain water management and policy developmentwater management and policy development