Post on 06-Oct-2020
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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