Can global models reproduce the current increase in western US wildfires and project a reliable future trend? Dominique Bachelet, Conservation Biology Institute Dave Conklin, Dept Biological and Ecological Engineering, Oregon State University Brendan Rogers and Maureen McGlinchy, Oregon State University Jim Lenihan, Ron Neilson, and Ray Drapek, PNW U.S. Forest Service

Why is it important? Fire causes change in albedo, so affects climate Fire can cause vegetation shifts Fire causes change in C stocks and sequestration potential important to be able to understand, simulate and project

Outline MC1 fire model Fire events in western US during the last decade Climate indices, fire and model results PDO and PNW, CA fires El Niño and PNW, CA fires Strengths and limitations of fire model Simulated fires respond to climate cycles in climate input data Strong climate signal overwhelms human impacts Carbon sequestration linked to climate and fire

MC1 Dynamic General Vegetation Model James Lenihan, Dominique Bachelet, Chris Daly, Ron Neilson (USFS and OSU) BIOGEOGRAPHY BIOGEOCHEMISTRY LIFEFORM COMPOSITION LIVE BIOMASS CLIMATE LIVE/DEAD BIOMASS REDUCTION NUTRIENT LOSS FIRE LIVE/DEAD BIOMASS SOIL MOISTURE LIFEFORM COMPOSITION VEGETATION STRUCTURE

Fire Module Fire area and behavior Fire effects Mortality Biomass Current Aboveground Carbon Pools Current Vegetation Type Current Weather Current Soil Moisture Fuel Loading Crown Structure Live and Dead Fuel Moisture Fire area and behavior Fire effects Mortality Biomass Consumption Emissions Nutrient Loss Fire Module

Outside the historical from Schoenagel et al. 2004 Canada 11 Western States Arizona and New Mexico Observed upward trend in wildfires in North America ? by American Forest Resource Council Outside the historical range of variation?

Pacific Decadal Oscillation (Mantua et al. 1997) and fires North Pacific monthly sea surface temperature variability Active suppression fuel accumulation Post-settlement fires Increase in fires Warm PDO Cool PDO Warm PDO Source: Jeremy Littell et al. 2009. Climate and wildfire area burned in western US ecoprovinces, 1916-2003. Ecological Applications.

Effects of PDO on Winter Precipitation Positive (warm) PDO dry wet fuel build-up dry fuels Standardized Precipitation Anomaly Negative (cool) PDO Standardized Precipitation Anomaly wet dry source: George Taylor, Corvallis

Pacific Decadal Oscillation and PNW fires Years with fires > 80,000 ha between 1916 and 1997 in National Forests source: Mote et al. 1999

Dynamic Global Vegetation Model MC1 Results at 3 spatial grains for the state of California

Dynamic Global Vegetation Model MC1 Results at 3 spatial grains Oregon and Washington ?

ENSO and fires (Westerling and Swetnam 2006) Credit: Tom Swetnam and Julio Betancourt. Updated from Swetnam, T.W., and J.L. Betancourt, 1990: Fire-Southern Oscillation relations in the southwestern United States. Science 249:1017-1020.

Effects of El Nino on Winter Precipitation and Temperature fine fuel build-up for La Nina fires drought set-up (reduced snowpack longer fire season) source: G. Taylor, Corvallis

La Nina 1973 1988 El Nino 2002 1987 1975 1998 1972 1997 1965 1982 2002 1987 strong El Nino years: 1972-73, 1982-83, 1991-92, 1997-98 La Nina years: 1955-56, 1973-74, 1975-76, 1988-89

Strengths and limitations of fire models

There are clear cycles in time series of fire and carbon: climate inputs matter Strong climate signal overwhelms human impacts: simulations match observations Carbon sequestration linked to climate and fire

Dynamic Global Vegetation Model MC1 run at 3 spatial scales - CA Connection with climate index at the coarser scale

Dynamic Global Vegetation Model MC1 run at 3 spatial scales- OR&WA Similar dynamics at all scales No obvious link to climate index

Dynamics show clear cycles: drought of the 1930s, signal in the early 1970s and 1990s (La Nina?) strong El Nino years: 1972-73, 1982-83, 1991-92, 1997-98 La Nina years: 1955-56, 1973-74, 1975-76, 1988-89

Observed vs Simulated Area Burned on Western USA Federal Lands 1916-2000 in million ha Observations: MC1 simulation at 8km, Lenihan

Simulated fires respond to climate cycles in climate input data: scale matters Strong climate signal can overwhelm human impacts but human actions may affect future fire regimes Carbon sequestration linked to climate and fire

Ignition limited (wet) Fuel limited SUPPRESSION IMPACT boreal, subalpine, tropical rain forests woodlands, high elevation forests INVASIVES FIRE SUPPRESSION IMPACT RAIN Fuel limited low elevation dry forests, savannas DROUGHT SUPPRESSION IMPACT source: Meyn et al. 2007 Progress in Physical Geography 31:287-312 (LIF=large intense fires)

Simulated fires respond to climate cycles in climate input data: scale matters Strong climate signal overwhelms human impacts but human actions may affect future fire regimes Carbon sequestration linked to climate and fire

vegetation dieback and/or soil carbon depletion Response to climate signal: interannual variations in C stocks vegetation dieback and/or soil carbon depletion warm wet hot dry cool dry hot dry wet cool wet cool wet cool * * SOIL GAIN LOSSES Yosemite NP Conklin unpubl.

1: what is fixed in a year is entirely released as fire emissions Fraction of Net Primary Production consumed by fire 1971-2000 1: what is fixed in a year is entirely released as fire emissions 2071-2099 CSIRO B1 HADLEY A1B MIROC A2 source: Dave Conklin, unpub.

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