Environmental Engineering Reference
In-Depth Information
in median annual averaged area burned in the western United States due to
a 1ºC global average temperature increase, using the temperature and pre-
cipitation patterns from the corresponding figures in Chapter 4. The increase
in median annual area burned ranges from 73% to over 600%, depending
on the ecoprovince. Aggregating all 14 ecoprovinces in which fire is most
sensitive to temperature variations, the net area burned by the median fire
increases from 572,000 ha for the reference period 1970-2003, to 1,800,000
ha with a 1ºC global average temperature increase.
Other investigators using different climate models and a variety also find
thata climate change will increase the risk of wildfire throughout the western
United States, so long as fuel is not limiting. For example, Spracklen et al.
(2009) used output from the GISS AGCM coupled to a slab ocean forced
by the A1B emission scenario with an empirical model very similar to that
used by Littell et al. (2009); they concluded that climate changes projected
for the mid-21st century would result in a 54% increase in total annual area
burned compare to that in the late 20th century, and burn areas doubling
in the Rockies and Pacific Northwest.
Similar studies have been done to examine how climate change will
affect forest wildfires in other regions of the world, including Australia,
New Zealand, the southern Mediterranean, and in boreal forests of Canada
(IPCC, 2007d). In general, these studies report wildfires will increase over
the course of the century due to projected climate changes from one or
more of the AR4 climate models using one or more of the marker emission
scenarios.
As the time horizon increases, a further complication arises in projecting
wildfires because of the importance of fuel availability and quality (moisture
content) for determining the likelihood and size of wildfires. Systematic
climate changes will inevitably alter the distribution of the vegetation, and
significant changes in the vegetation would greatly affect the potential for
wildfires and the wildfire area burned. For example, if climate change fur-
ther dries already arid grasslands, then the grasslands will wither to deserts
and fire will no longer be supported. On the other hand, if climate change
changes the distribution of pest and pathogens such that forests become dis-
eased, then additional fuel will be made available due to forest dieback (see,
e.g., discussion of the bugs in the BC/AK spruce) and fires will be enhanced
until the extra fuel is exhausted and replaced by woodlands or grasslands.
To date, all of the statistical models for wildfire do not admit changes in
vegetation type due to the ecosystem response to climate change.
