Jeremy Littell, USGS
Alaska Climate Science Center
Don McKenzie, USFS

Climate(impacts(on(fire:(( ecosystem2dependent(non2lineari4es(
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Forested
Systems:
water deficit decreases fuel moisture, increases fuel availability
Littell, McKenzie, Peterson, Westerling (2009)
Map: R. Norheim
Climate and fuels will both change under climate change, and the relationship between them may not be linear.
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Non-forest: water- facilitated fuel availability
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Increasing temperature !
Decreasing precipitation !

Adaptation and planning for future climate impacts depends on ecologically plausible vegetation dynamics.
Projecting components of fire regimes – frequency, size, severity, intensity, rotation – is important.
The more we think we understand, the more we need to ask – “Is a statistical approach to future fire warranted?”

Water(balance(as(a(control(on(wildfire (
Water balance deficit:
Potential – actual evapotranspiration !
•   Deficit is a good correlate relating fire and climate
•   Units relate both energy / water demand (PET) and water supply (AET)
•   Direct conceptual and mechanistic link to plant performance and fuel availability
•   +Deficit = more drought; - deficit = surplus
JJA Historical Deficit
Map: R. Norheim
Elsner'et'al.'2010,'Li1ell'et'al.'2011'

JJA water balance deficit (2040s A1B)
Data:%G.%Mauger.%Map:%R.%Norheim%%Funding:%USFS,%DOI%PNW%CSC%

Projected ecosection water balance trajectories
Bailey ecosections
Map: R. Norheim
Ecosec'on!PET!and!AET!averages.!A1B,!composite!of!10!downscaled!CMIP3!GCMs,!!
VIC!aCer!Elsner!et!al.!2010,!LiFell!et!al.!2011,!Hamlet!et!al.!2013.!Data:!G.!Mauger!

Projected(summer(water(balance(deficit(increases( for(most(ecosec4ons(
Ecosec'on!PET!and!AET!averages.!A1B,!composite!of!10!downscaled!CMIP3!GCMs,!!
VIC!aCer!Elsner!et!al.!2010,!LiFell!et!al.!2011,!Hamlet!et!al.!2013.!Data:!G.!Mauger!

Fire'models:'Li1ell'and'Gwozdz,'2011.'Climate:'(36'A2'scenarios)'of'hydroclimaDc'projecDons'from'LLNL'and'USBOR.''

PNW(ecosec4on(( fire(rota4ons(
The!'me!required!to!burn!an!
area!equivalent!to!the!study!
area!(ecosec'on)!varies.!!
!
Cumula've!area!burned!
approaches!ecosec'on!area!
by!the!2040s!for!some!forest!
systems.!Some!are!radically!
exceeded!by!the!2080s.!
!
Simple!bestUfit!models!with!
only!Tmax!(M333C,!342B)!or!
PET!(342D)!subject!to!
thresholds!and/or!overU
predict.!
Fire'models:'Li1ell'and'Gwozdz,'2011.'Climate:'(36'A2'scenarios)'of'hydroclimaDc'projecDons'from'LLNL'and'USBOR.''

Projec4ng(PNW(fire:(( climate(models(and(water(balance((
Along!a!gradient!of!
historical!(1950U2000)!
water!deficit!in!the!
Pacific!Northwest,!
climate!change!would!
increase!the!area!
burned!up!to!about!
200mm!deficit.!
!
The!increases!in!area!
burned!are!less!at!
opposite!ends!of!the!
gradient.!
Fire'models:'Li1ell'and'Gwozdz,'2011.'Climate'ensemble(120+'scenarios)'of'hydroclimaDc'projecDons'from'USBOR,'LLNL.''

H a
:!Overpredict!<2040!
Reason:!Δ!fuel!sensi'vity!
H a
:!Underpredict!
Reason:!Threshold!availability!
H a
:!Good!<2040;!underpredict!>!>!
Reason:!Monsoon!precip!Δ!
H a
:!Good!<2040;!overpredict!>!
Reason:!Vegeta'on!Δ!
Statistical fire projections make qualitative assumptions similar to bioclimatic envelope models for tree species.
This leads to less than ideal statistical and ecological assumptions underlying the projections.
The time to emergence concept is useful for defining the limits of useful models into the future.

Acknowledgements: Rich Gwozdz; Phil Duffy, LLNL; Guillaume Mauger, UW-CIG; jittell@usgs.gov