Headwaters Hydrology: Principles to Policy John Pomeroy Canada Research Chair in Water Resources and Climate Change Centre for Hydrology University of Saskatchewan, Saskatoon

Purpose of Talk Outline the hydrological principles governing water cycling and streamflow generation in mountain headwater basins Outline the hydrological principles governing water cycling and streamflow generation in mountain headwater basins Investigate the impacts on hydrological cycling of changing forest cover and climate Investigate the impacts on hydrological cycling of changing forest cover and climate Note the challenges to preserving the hydrological cycle in this region Note the challenges to preserving the hydrological cycle in this region Outline some management practices to meet current and anticipated challenges in the Rockies Outline some management practices to meet current and anticipated challenges in the Rockies Suggest some policy options Suggest some policy options

Canadian Rockies are the Hydrological Apex of North America

Rocky Mountains Headwaters: Source of the Saskatchewan-Nelson

Saskatchewan, where it heads (if it can)

Hudson Bay (where it controls sea ice, ocean salinity and the global climate system)

Cold Regions Hydrological Cycle Interflow Runoff Snowfall Sublimation Blowing Snow Evaporation Rainfall Snowmelt Infiltration to Frozen Ground Groundwater Flow Precipitation Ice Lakes

snowmelt in mountains Rocky Mountain Runoff is Mostly Snowmelt Surface Runoff Groundwater Discharge

How Much Snow is There? Less and Less….. US NOAA satellite measured average change (days/yr) in snow cover duration (Feb.-Jul.) over the period Rockies: 1 to 2 month decrease!

Marmot Creek Research Basin m.a.s.l. Kananaskis Valley, Bow River m.a.s.l. Kananaskis Valley, Bow River Alpine Alpine Subalpine Subalpine Montane Montane Clearcut Clearcut Meadow Meadow +600 mm precipitation +600 mm precipitation 70% snowfall 70% snowfall ~50% runoff ~50% runoff Marmot Basin Bow River valley Kananaskis River valley

Airborne LiDAR Snow 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 Forest Snow – Open Snow

Snow Accumulation Variability

Blowing Snow in Mountains Inter-basin water transfer Transport of snow to deep drifts Supports glaciers, late lying snowfields, contributing areas Water supply to sub- alpine forests Melt controls summer streamflow

Blowing Snow Entering Basin

Alpine Tundra Ridgetop – most snowfall eroded by blowing snow

Blowing Snow Transport Over Complex Terrain Q SUBLIM Q TRANSP TOPOGRAPHIC DEPRESSION WINDWARD HILL LEEWARD HILL GRASSFORESTBARE GROUND SHRUB Q SUBLIM Q TRANSP WINDWARD HILL, BARE GROUND, GRASS LEEWARD HILL, FOREST SHRUB, DEPRESSION BLOWING SNOW IF CAPACITY/THRESHOLD IS EXCEEDED MacDonald, Pomeroy, Pietroniro

Linear simulation of westerly flow over Mountain Ridge and Valley WindspeedWind Direction 3 km Gridded 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 Icefields Mapped from NASA LANDSAT satellite Glaciers are fed by alpine snow, esp. wind drifted snow 36% loss of glaciated area of South Sask Basin Demuth & Pietroniro

Alpine Snow Challenges Seldom monitored – valley bottom snow stations are not good indicators for the alpine, sparse snow surveys Seldom monitored – valley bottom snow stations are not good indicators for the alpine, sparse snow surveys 1 Environment Canada weather station in alpine zone 1 Environment Canada weather station in alpine zone Observed glacier decline is associated with reduced alpine snow accumulation Observed glacier decline is associated with reduced alpine snow accumulation Inadequate understanding of alpine snow dynamics Inadequate understanding of alpine snow dynamics Not incorporated in most climate and hydrology models Not incorporated in most climate and hydrology models Impacts of Climate Change? Impacts of Climate Change? Warmer winters and more lush alpine vegetation reduce blowing snow redistribution Warmer winters and more lush alpine vegetation reduce blowing snow redistribution Less snow redistributed to glaciers Less snow redistributed to glaciers More snow at high elevation and less at treeline More snow at high elevation and less at treeline Stronger Chinooks increase sublimation loss Stronger Chinooks increase sublimation loss Less snow on windward slopes and in cornices Less snow on windward slopes and in cornices

Intercepted Snow in Forests Snow intercepted in canopies for weeks in cold periods Snow intercepted in canopies for weeks in cold periods Snow does not blow from forest canopies to clearings in any significant quantities Snow does not blow from forest canopies to clearings in any significant quantities Intercepted snow is well exposed to sunlight and dry winds Intercepted snow is well exposed to sunlight and dry winds

Interception Efficiency = interception/snowfall (I/P) More snow is trapped by denser forests Snow is trapped more efficiently from light snowfalls spruce pine burned Hedstrom and Pomeroy

Intercepted Snow Sublimation Thermal Infrared Image Intercepted snow is cool

Snow Interception & Sublimation Loss in Marmot Creek MacDonald & Pomeroy

Interception & Sublimation of Snow on a Weighed Hanging Tree

Effect of Forest Removal on Snow Accumulation Sparsely Wooded Medium Density, Young Dense Mature Canopy Deforestation Effect

Snow Interception and Sublimation in Rocky Mountain Forests Intercepted snow sublimation loss up to 60% of seasonal snowfall in the Rockies Intercepted snow sublimation loss up to 60% of seasonal snowfall in the Rockies Any disturbance that reduces coniferous canopy cover will increase snow accumulation Any disturbance that reduces coniferous canopy cover will increase snow accumulation Climate and Forest Change Impacts? Climate and Forest Change Impacts? Reduction in forest cover due to pine beetle, fire, clearing will dramatically reduce sublimation losses Reduction in forest cover due to pine beetle, fire, clearing will dramatically reduce sublimation losses Needle removal with standing deadwood will more than double snow accumulation Needle removal with standing deadwood will more than double snow accumulation Sublimation losses insensitive to temperature Sublimation losses insensitive to temperature

Snowmelt Incoming solar and thermal radiation Incoming solar and thermal radiation Warm air masses Warm air masses Energy storage Energy storage Terrain and vegetation effects Terrain and vegetation effects

Snow Energetics

Alpine Snowmelt: Solar Radiation & Convective Heat Transfer Alpine Snowmelt: Solar Radiation & Convective Heat Transfer 20 o slopes South Face North Face Valley Bottom Solution: landscape units

May 8, 2007 Jul 4, 2007 Jun 2, 2007 Cirque SCA fraction

08-May 02-Jun 04-Jul De Beer & Pomeroy Snowcover Depletion in Alpine Basins 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 Simulated Solar Radiation for Snowmelt Clear Overcast Possible to estimate solar and thermal radiation even in patchy forests if LiDAR inventories of forest structure are available Essery & Pomeroy

Hot Trees – Thermal Radiation

Thermal Radiation from Pine Forest temperatures enhanced above air temperature by extinction of solar radiation Thermal radiation from forests greatly enhances melt compared to open environments

Forest Density Impacts Snowmelt Energy Clearing Mature Forest Net radiation = solar + thermal radiation Ellis & Pomeroy

Snowmelt Runoff Generally Increases with Decreasing Forest Cover Low forest density associated with high soil moisture, deep snow and rapid melt

Snowmelt and Runoff Snowmelt in Rockies is solar and thermal radiation driven in forests, with wind effects in alpine and clearings Snowmelt in Rockies is solar and thermal radiation driven in forests, with wind effects in alpine and clearings Slope and aspect differences Slope and aspect differences Sensitive to presence of vegetation cover Sensitive to presence of vegetation cover Forest melt is insensitive to air temperature Forest melt is insensitive to air temperature Clearing/alpine melt is sensitive to air temperature Clearing/alpine melt is sensitive to air temperature Forest clearing on south facing slopes and level sites accelerates melt Forest clearing on south facing slopes and level sites accelerates melt Forest clearing on north facing slopes decelerates melt Forest clearing on north facing slopes decelerates melt Higher snow accumulation and melt rates from forest removal cause greater runoff quantities in spring Higher snow accumulation and melt rates from forest removal cause greater runoff quantities in spring

Hydrological Change in the Headwaters Need continuous research basin records Marmot Creek – the only long term research basin in the Canadian Rocky Mountains IHD IP Reconstruction of temperature and streamflow

Temperature Trends at Elevation in Marmot Creek, 1962-Present Winters are warmer by 3 to 4 o C since the 1960s Harder & Pomeroy

Annual Precipitation in Kananaskis Cycling but no statistically significant trend, wetter since 1960s Harder & Pomeroy

Rainfall versus Snowfall, Kananaskis Valley Warmer winters = less snowfall Warmer winters = more rainfall Temperature Change Harder & Pomeroy

Cycling but No Trend in Timing of Peak Streamflow from Marmot Creek Day of year of peak streamflow, Middle Creek Harder & Pomeroy

Marmot Creek Spring Peak and Annual Streamflow Decline of ~30% Since 1960s Middle Creek June Streamflow cubic metres/second Harder & Pomeroy

Marmot Creek Climate Change Implications for Water Policy Warmer winters Warmer winters Less snowfall, more rainfall Less snowfall, more rainfall Peak streamflows 30% smaller than 1960s Peak streamflows 30% smaller than 1960s Summer streamflows 29% smaller than 1960s Summer streamflows 29% smaller than 1960s No change in timing of peak streamflow No change in timing of peak streamflow Less mountain streamflow available for filling reservoirs, irrigation, communities, ecosystem needs, oceans, etc. Requires adaptation NOW. Less mountain streamflow available for filling reservoirs, irrigation, communities, ecosystem needs, oceans, etc. Requires adaptation NOW. Careful, only one site – regional variation unknown. Careful, only one site – regional variation unknown.

Deforestation

Forest Management? Possible to double snow accumulation through forest thinning, partial clearing or permitting disease or fire Possible to double snow accumulation through forest thinning, partial clearing or permitting disease or fire Possible to retain low snowmelt rate by retaining some canopy structure (thinning, standing deadwood, shelterwood) Possible to retain low snowmelt rate by retaining some canopy structure (thinning, standing deadwood, shelterwood) Careful! At Marmot direct impacts on annual streamflow from cutting in early 1980s were difficult to measure. But it works in the Upper Colorado….. Careful! At Marmot direct impacts on annual streamflow from cutting in early 1980s were difficult to measure. But it works in the Upper Colorado….. Careful! Can contribute to flooding, erosion, ….. Careful! Can contribute to flooding, erosion, ….. Careful! Forest cover removal will increase sensitivity of melt timing and rate to climate warming Careful! Forest cover removal will increase sensitivity of melt timing and rate to climate warming Careful! We have inadequate monitoring and predictive capacity to prescribe this safely and with any reasonable confidence Careful! We have inadequate monitoring and predictive capacity to prescribe this safely and with any reasonable confidence

Science Policy Implications Urgent to Urgent to confirm hydrological response from forest manipulation trials conducted in Marmot Creek in the 1980s. Streamflow observations stopped in confirm hydrological response from forest manipulation trials conducted in Marmot Creek in the 1980s. Streamflow observations stopped in examine hydrological response to forest change in main ranges as well as front ranges examine hydrological response to forest change in main ranges as well as front ranges better quantify and understand changes to alpine snow and glacier hydrology from changing high altitude climate better quantify and understand changes to alpine snow and glacier hydrology from changing high altitude climate Improve and test predictive models so that virtual simulations can be conducted of coupled climate, glacier and forest change Improve and test predictive models so that virtual simulations can be conducted of coupled climate, glacier and forest change Restoration of network of IHD Basins in the Rockies with site selection keyed to major policy uncertainties Restoration of network of IHD Basins in the Rockies with site selection keyed to major policy uncertainties Enhancement of our networks that measure, monitor and observe hydrology and meteorology in mountains especially at high elevations Enhancement of our networks that measure, monitor and observe hydrology and meteorology in mountains especially at high elevations

How to Better Observe and Predict? Focussed Experiment Area to couple key issues Focussed 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 plains) Downstream drought and water supply (intermountain interior and northern plains) International Waters International Waters Rocky Mountain Hydrometeorological Observatory Rocky Mountain Hydrometeorological Observatory Coordinated, integrated observations Coordinated, integrated observations Surface water, groundwater, snow & ice Surface water, groundwater, snow & ice Remote sensing Remote sensing Research basins Research basins Regional Data Assimilation & Prediction Regional Data Assimilation & Prediction Information Portal Information Portal Information Interpretation Information Interpretation Emphasis on water security and climate change impacts Emphasis on water security and climate change impacts

Concluding Remarks Snowpacks and vegetation, play an important role in governing Rocky Mountain streamflow Snowpacks and vegetation, play an important role in governing Rocky Mountain streamflow Physically-based computer models are having initial successes in estimating these effects for water resource prediction Physically-based computer models are having initial successes in estimating these effects for water resource prediction Climate change is reducing snowmelt and streamflow in headwater basins Climate change is reducing snowmelt and streamflow in headwater basins Forest management might mitigate some of the streamflow reduction, but has risks Forest management might mitigate some of the streamflow reduction, but has risks Both our observation and hydrological modelling capacities will require further development to meet the emerging needs of Rocky Mountain water management and policy development Both our observation and hydrological modelling capacities will require further development to meet the emerging needs of Rocky Mountain water management and policy development