Agriculture Reference
In-Depth Information
Box 1.1 The Mediterranean-type Climate
The mediterranean-type climate (MTC) is characterized by winter rains and
summer drought. Both winter growing conditions and summer drought con-
tribute to making these landscapes some of the most fire-prone in the world.
Coastal influence moderates winter temperatures so that rains coincide with
suitable growing temperatures (
Fig. B1.1.1
). Due to this extended winter-spring
growing season, primary productivity is moderately high for semi-arid regions
and vegetation forms dense, sometimes impenetrable thickets that, when dry,
contribute to fire spread. The annual summer drought reduces fuel moisture to
levels conducive to rapid ignition. This MTC is the result of global circulation
patterns that generate a summer high pressure cell of dry sinking air that blocks
incoming summer storms on the western sides of continents concentrated
between 32
and 38
N or S latitude. Globally there are five subtropical high
pressure cells that lie within these latitudes during the summer and migrate
toward the poles during the winter, creating a MTC in: the Mediterranean
Basin, California, central Chile, the southwestern portion of the Western Cape
Province of South Africa, and the southwestern portion of Western Australia
and South Australia plus adjoining portions of the province of Victoria.
The seasonal distribution of precipitation and temperature illustrated for
Los Angeles (
Fig. B1.1.1
) is mirrored in the other MTC regions. However,
despite the similarities, there are climatic differences (
Table B1.1.1
) that may be
expected to affect fire regimes. For example, much of California and parts of
Chile and the Mediterranean Basin have the most severe summer droughts,
often with several months of no rainfall, although there is much intraregional
variation. For example, interior parts of the western Mediterranean Basin may
have significant summer precipitation; summer rain as a percentage of annual
total is 21% for Valencia, Spain, 12% Marseille, France, or 10% Rome, Italy
(Mu
¨
ller
1982
). In Chile, the MTC spans a large latitudinal range although the
proportion of summer precipitation increases poleward. In the south, where the
Andean range is lower, the MTC may extend eastward into Argentina, as is
evident at Bariloche, Argentina (41
S latitude) with about 700 mm rainfall and
less than 10% in summer (Mu¨ ller
1982
). In both South Africa and southern
Australia summer precipitation increases eastward, although seasonal patterns
are less predictable and summer droughts occur in some years. In South Africa
the MTC region is more or less restricted to the southwestern Cape region; just
4 degrees of longitude east of Cape Town, the amount of summer rain more
than triples at Oudtshoorn (
Table B1.1.1
).
Winter precipitation likewise varies between MTC regions comprising over
two thirds of the annual total in the easternMediterranean Basin, California and
central Chile. In Seville, Spain, the autumn precipitation equals the winter total
and in Adelaide, South Australia, spring and autumn precipitation are equal and
Continued
