Climate change, growth, and California wildfire

Large wildfire occurrence and burned area are modeled using hydroclimate and landsurface
characteristics under a range of future climate and development scenarios. The range of
uncertainty for future wildfire regimes is analyzed over two emissions pathways (the Special
Report on Emissions Scenarios [SRES] A2 and B1 scenarios); three global climate models (Centre
National de Recherches Météorologiques CM3, Geophysical Fluid Dynamics Laboratory CM21
and National Center for Atmospheric Research PCM2); a mid-range scenario for future
population growth and development footprint; two model specifications related to the
uncertainty over the speed and timing with which vegetation characteristics will shift their
spatial distributions in response to trends in climate and disturbance; and two thresholds for
defining the wildland-urban interface relative to housing density. Results were assessed for
three 30-year time periods centered on 2020, 2050, and 2085, relative to a 30-year reference
period centered on 1975. Substantial increases in wildfire are anticipated for most scenarios,
although the range of outcomes is large and increases with time. The increase in wildfire area
burned associated with the higher emissions pathway (SRES A2) is substantial, with increases
statewide ranging from 57 percent to 169 percent by 2085, and increases exceeding 100 percent
in most of the forest areas of Northern California in every SRES A2 scenario by 2085. The spatial
patterns associated with increased fire occurrence vary according to the speed with which the
distribution of vegetation types shifts on the landscape in response to climate and disturbance,
with greater increases in fire area burned tending to occur in coastal southern California, the
Monterey Bay area and northern California Coast ranges in scenarios where vegetation types shift more rapidly.