Mediterranean-type Climate Ecosystems and Fire - Fire in Mediterranean Ecosystems - page 19

Box 1.3 Fire Weather Winds in MTC Regions
Regardless of where you are in the world, large uncontrollable fires usually are
driven by high winds. Most MTC regions have extreme wind events that typic-
ally last a few days and may occur many times in a year, although are usually
concentrated in particular seasons ( Table B1.3.1 ). When these winds coincide
with droughts and ignitions they are associated with extreme fire events, charac-
terized by high rates of spread, long flame lengths, long-distance spotting and
presence of fire whirls and other unpredictable wind patterns.
Katabatic or downslope winds are pushed over the leeward sides of mountains
and heat at the dry adiabatic lapse rate as they descend. They are typically
associated with a reversal from onshore to offshore airflow. Sometimes these
are localized events such as the Sundowner Winds near the town of Santa
Barbara in California (Blier 1998 ).
Other winds develop from synoptic weather conditions known as foehn wind
events where interior high pressure cells are juxtaposed with low pressure troughs
on the coastal side of mountains. Examples include the southern Europe mistral
winds and southern California Santa Ana winds among others noted in Table
B1.3.1 . Topography plays a key role in the development of these foehn winds and
their ultimate trajectory to the coast (Fosberg et al . 1966 ; Schroeder & Buck
1970 ). The mistral winds are funneled down the Rhone River Valley and the
Santa Ana winds follow the Santa Ana River Valley, although these winds follow
other drainages as well and their ultimate manifestation is a result of local terrain
(Whiteman 2000 ; Moritz et al . 2010b ).
When fires are ignited during these extreme winds they produce severe burning
conditions sometimes referred to as firestorms (e.g. Fig. B1.3.1 ). Foehn winds are
associated with extreme fire weather in many parts of the world. They contribute
to most of the area burned in regions such as southern California (Keeley 2006a ;
Moritz et al . 2010b ), in part because the winds are an annual event each autumn
(Lessard 1988 ; Raphael 2003 ). Mistral winds and the similar sharav winds in the
eastern Mediterranean Basin are also annual events contributing to extreme fire
danger every year (Kutiel & Kutiel 1991 ) and they too account for the bulk of
area burned (Levin & Saaroni 1999 ). The bergwinds of South Africa are associ-
ated with fires frequent enough to shape landscape patterns of forests and
shrublands (Geldenhuys 1994 ). Southern-ocean cold fronts in spring and
summer produce strong, hot dry brickfielder winds across southeastern Australia
and promote the rapid development of large, intense fires, which are invariably
associated with major losses of life and property (Hasson et al . 2009 ). However,
in this non-MTC region, these are not annual events (Sharples et al . 2010 ) .
Other weather anomalies appear to be equally important as foehn winds in fire
activity on the Iberian Peninsula (Milla ´ n et al . 1998 ). In southwest Australia
roughly once a decade strong hot winds associated with tropical cyclones bring
gale force winds onshore during summer and create extremely hazardous fire
conditions resulting in firestorms (McCaw & Hanstrum 2003 ).
Continued