Fire and Climate Change in Washington Jeremy S. Littell JISAO CSES Climate Impacts Group University of Washington

Water balance and fire Water balance deficit is the difference betweenatmospheric demand for waterand the water available tosatisfy that demand As deficit increases, fuelmoisture typically decreases Different fuel types responddifferently: dead and fine fuelsvs. foliage WACCIA 12 Feb 2009

Area burned in 11 Western states, * 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 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 systems Littell, McKenzie, Peterson, and Westerling. In press.

Projecting future area burned WACCIA 12 Feb th century climate and fire: build a model –Regional: precip. and temp. ( ) –Sub-regional: precip., temp., water balance deficit variables ( ) 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