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