4. Drought increases wildfire
Fire is one of the most important disturbances in terrestrial
ecosystems on a global scale [56] and contributes significantly to
the budgets of several trace gases and aerosols [2]. It is generally
asserted that anthropogenic climate change will lead to widespread
and more frequent fires [15] and that this rise will be
related to changes in rainfall and increased temperatures,
especially as they lead to drought conditions in areas with
abundant fuel loads [62].
The relationship between drought and wildfire has been discussed
for many years. Although the connection between drought
and fire is intuitive, the mechanisms behind regional patterns of
drought are very complex [48]. It is difficult to determine how
many fires are directly caused by drought, several studies have
proven that drought is an important driving force for fire
[25,56,59]. Drought-induced wild fires have been associated with
global circulation anomalies such as the El Niño–Southern Oscillation
[55] and, more recently, the Pacific Decadal Oscillation [25]
and the SSTS in the North Atlantic [18]. In several case studies in
southern Borneo, a strong coupling between regional drought
intensity and fire emissions has been found by van Der Werf
[56]; forest loss rates and areas of vulnerable peatland both
increase in drought years. Data collected from tree-ring analyses
were used to reconstruct the PDSI and forest fire events over the
period 1700–1975 in the U.S. southwest, further supporting the
correlation of drought and fire [48]. Studies in California [30],
Washington [25], and the American Rocky Mountains [48], have
all arrived at similar conclusions.
Fire influences the climate system through the release of carbon
and atmospheric aerosols and through changing the surface
albedo. Although wildfires are usually contained to a tiny area of
the globe, they can have huge impacts on the global carbon cycle
[47]. Currently, all sources of fire create CO2 emissions almost
equal to 50% of those coming from fossil-fuel combustion
(2–4 Pg C year1 versus 7.2 Pg C year1) [11]. During the period of