Fire and Climate Change in Washington

Jeremy S. LittellJISAO CSES Climate Impacts Group

University of Washington

Water balance and fire

• Water balance deficit is the difference between atmospheric demand for water and the water available to satisfy that demand

• As deficit increases, fuel moisture typically decreases

• Different fuel types respond differently: dead and fine fuels vs. foliage

WACCIA 12 Feb 2009

WACCIA 12 Feb 2009

Area burned in 11 Western states, 1916-2007*

Littell et al. in press

Regional fire and climate change

WACCIA 12 Feb 2009

• As temperature increases, the atmosphere evaporates more water from the landscape, plant tissues, and fine fuels

• This produces larger than normal, and more connected areas of depleted fuel moisture during the fire season

• Regional synchronization of fuel availability occurs

• Fire “blowups” are driven by extreme weather, but are contingent on climatically-driven fuel moisture.

MODIS, Northern Rockies, July 2003MODIS, Northern Rockies, July 2003

Fuels and ecosystem pattern influence

how climate affects fire

WACCIA 12 Feb 2009

• Different fuel types respond differently to climate

• Two mechanisms: drying of fuels and production of fuels

• Fuel (moisture) - limited systems

• Climate (energy) - limited systemsLittell, McKenzie, Peterson, and Westerling. In press.

Projecting future area burned

WACCIA 12 Feb 2009

• 20th century climate and fire: build a model

– Regional: precip. and temp. (1916-2006)

– Sub-regional: precip., temp., water balance deficit variables (1980 - 2006)

• Projected climate for the 2020s, 2040s, and 2080s

• Use model to project fire into future given future climate

WACCIA 12 Feb 2009

Projections of future regional area burned

• Historical average: 425,000 acres– 2020s: 0.8 million– 2040s: 1.1 million– 2080s: 2.0 million

• Probability of a year >> 2 million acres:– Historical: 5%– 2020s: 5% (1 in 20)– 2040s: 17% (~1 in 6)– 2080s: 47% (~1 in 2)

Best model (tie): summer precip + summer temp OR summer water balance deficit

WACCIA 12 Feb 2009

Future area burned: Bailey’s ecosections

Ecosection fire results

• All models had important “water limitation” terms: summer water demand, maximum temperature, or water deficit.

• Okanogan highlands, Columbia basin, and Palouse prairie all show some evidence of climatic facilitation (wetter seasons prior to fire lead to more area burned)

• Coast range/Olympics and Puget/Willamette did not yield models, but big fires have occurred in last several hundred years.

Uncertainties and implications

• Uncertainties:– Disturbance synergies, interactions with and

limitations of vegetation– West-side sensitivity is possibly “threshold”, and

statistical fire models do a poor job

• Implications:– Rate of vegetation and landscape change would

potentially be much faster than species change alone.

– Large fires are destructive, but potentially an opportunity to affect ecosystem trajectories too - if new varieties or new species are planned, conversion can be faster.

Summary: HB1303 Forest Ecosystems

• Increased summer temperatures lead to increased water deficit and increased climatic stress for trees.

• This leads to changes in species distribution, but more importantly, to:– Increases in pine beetle host vulnerability– Shifts to higher elevations of pine beetle range– Increases in regional area burned– Increases in area burned in WA ecosections

• Implications are that “stress complexes” will be strong agents of landscape change by midcentury