fire and climate change in washington jeremy s. littell jisao cses climate impacts group university...
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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