snow accumulation, melt and sediment dynamics after ... · snow accumulation, melt and sediment...

Snow Accumulation, Melt and Sediment Dynamics After Wildfire in Rocky

Mountain Watersheds

C.Williams, U.Silins, M.Wagner, A.Martens, K.Herlein, S.Spencer, M.Emelko, M.Stone, A.Anderson, K.Bladon, & A.Collins

Outline

• Introduction – SRWP• Wildfire Trends – North

America• Wildfire & Hydrology

– Snow Accumulation– Post-wildfire Runoff– Sediment Dynamics

• Current Work (Waterton)• Conclusions

Photo source: https://torontosun.com/2014/07/16/forest-fires-continue-to-rage-in-nwt-evacuation-orders-issued-in-bc/wcm/2a4aba6f-9077-45dc-986e-929549eee7cd

Southern Rockies Watershed Project

Wildfire Trends

• Annual area burned rapidly increasing.

Wildfire Costs – U.S. Forest Service• Wildfire consuming budget of Forest Service.

• Reductions in budgets for everything else (e.g. watershed management, roads, etc.)

Source: The Rising Cost of Wildfire Operations (https://www.fs.fed.us/sites/default/files/2015-Rising-Cost-Wildfire-Operations.pdf)

Alberta Wildfire Size

Alberta Wildfires & Size Classes

• > 90% of fires are < 1 ha.

• < 0.2 % of fires account for >95% area burned.

Source: https://albertawater.com/water-yield-streamflow-analysis (Dr. Stefan Kienzle)

• Vast majority of water supply for Southern Alberta is generated in the mountains.

• Dark blue colour represents highest-yielding areas.

• 363 (m3/km2/yr) x 1000 north of Hwy 3 (Crowsnest Pass) to 1084 (m3/km2/yr) x1000 south of Waterton (Montana).

• For comparison, red areas around Lethbridge are 0 or even negative.

Water Yield – East Slopes

Wildfire and hydrology

Source: Onodera and Van Stan 2011.

Before Fire After Fire

Snow Interception & Sublimation

• Conifers capable of large degree of snow interception.

• Much of this sublimates, representing a loss of SWE.

• 40% of overwinter snowfall can be lost.

Pomeroy et al. 1998

https://cloudsat.atmos.colostate.edu/snow/Verseghy_polar_snowfall.pdf

40%

31%

Wildfire Effects on Snow Accumulation• Snow courses measured near peak SWE each

year (2005-2014… and continuing).

• 50 depth, 10 density measurements for each stand condition (burn, reference).

Peak snow accumulationSn

ow d

epth

(m)

0.0

0.5

1.0

1.5

2.0

Snow

wat

er e

quiv

alen

t (m

m)

0

100

200

300

400

500

600 ReferenceBurned

2005 2006 2007 2008 2010 2011 2012 2013 20142009

• Interception capacity greatly reduced after wildfire.

• Mean annual SWE (2005-2014): Burned stand = 347mm Reference stand = 195 mm

• 78% higher in burn (152 mm or 6”).

Post-wildfire Snow Water Equivalent

Source: Maxwell et al. 2019

• 5 studies found increase in SWE (7% –78%).

• One study found 10% decrease, and one found no change in SWE.

Maxwell et al., 2019+50% & 58%+78% (10 yr. mean)

+25%

+11% +7%

-10%

No Change

SWE in burn compared to reference

Our results 49.4 1700 m 78% Increase in burned forest

Snowmelt• 30% more energy available for melt in burn.

• Earlier date of complete snowpack removal. Burn, Reference

(2009): May 24, May 31 (7 days)(2010): May 15, May 28 (13 days)

Source: Burles & Boon 2011

Streamflow Measurement• SRWP crew has measured streamflow 12 – 18 times

per year for each of the 5 streams included here.

• Constructed new rating curves every season.

• Stream stage measured every 10 minutes with instream sensors.

Weekly Water Yields After 2003 Lost Creek Wildfire

• 52% of Apr-Oct yield produced from Apr. 2 to Jun. 10 in burn.

• Only 20% for reference streams. Takes until the Jun. 18-24 week to surpass 52% of reference yield.

10-year Mean Weekly Yields (2005-2014)

Rain on Snow

• Caveat to the “normal” snowmelt season – rain on snow.

• Can cause extreme runoff.

• Willamette Falls, Oregon City.

http://www.oregon.com/attractions/willamette-falls

https://www.oregonlive.com/history/2016/02/oregon_flood_of_1996_20_years.html

Rain on Snow

-211 mm

-48 mm

Source: Marks et al. 1998

Source: Marks et al. 1998

Melt Timing & Sediment Delivery

Large effect of fire on sediment production

Strong incremental effect of post-fire salvage logging

Exceedingly long lasting (> decade)

Silins et al. 2008, 2009a, 2009b, Wagner et al. 2014

Suspended sediment and turbidity

SedimentaryMetamorphicIgneous – intrusiveIgneous - extrusive

Bedrock geology

Fine grained sediments play a much bigger role than in many other regions.

Suspended sediment and turbidity

Phosphorus

Strongly associated with fine sediment

No evidence of “recovery” in > 10 yr.

Total Phosphorus

Silins et al. 2014, Ecohydrology

Phosphorus

Strongly associated with fine sediment

No evidence of “recovery” in > 10 yr.

Nutrient poor “oligotrophic” streams before fire – “mesotrophic” or even “eutrophic” after fire

Total Phosphorus

Silins et al. 2014, Ecohydrology

SRWP Phase III: Kenow Fire

Summary

• Wildfires trending towards larger and more frequent.• More snow accumulation in fire-affected forests.• Highly variable, but Canadian studies show 25% to

nearly 80% increase when compared with reference.• However, the snowpack melts faster in burned

watersheds moving water out 1-2 weeks faster.• 5 – 20 x higher sediment contributions from burned

catchments – long lasting.• Data set from Kenow fire in the works.

Ongoing Partnerships

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