Agriculture Reference
In-Depth Information
“
Aseasonal” climate
Winter-drought climate
Typical year
Summer-drought climate
Anomalous year
Fig. 10.1
Schematic model of changes in drought-prone landscape under different climatic
regimes. Aseasonal climates are those that, on average, have precipitation in all seasons of the
year and droughts are not annual events but may occur multiple times a decade, whereas the
other two climates have regular annual droughts. Depending on structural characteristics of the
vegetation and seasonal distribution of lightning ignitions, these drought-prone sites are also
likely to be fire-prone sites
.
Origin of the Mediterranean-type Climate
Climatic seasonality and soil nutrient stress are key to understanding the origin of
fire-prone MTV, and these certainly precede the MTC in all regions. Such climatic
characteristics have waxed and waned with movement of the continents, changes
in ocean circulation, orogeny, earth orbital patterns and associated factors
(Parrish
1998
). The MTC, by having an annual drought in the hottest months of
the year, has greatly expanded fire-prone landscapes (Fig. 10.1).
In prior discussions on the timing of MTC origins, there has been some level of
disagreement in the scientific literature and part of this is semantic in that authors
have focused on different questions. For example, in discussing origins of the
MTC Axelrod (e.g.
1973
) considered the timing of the MTC in coastal California
regions, whereas other authors have taken a more global perspective on the
paleohistory of this climatic pattern, such as Beard (
1977
) who considered the
question of a MTC in Australia, which appears to have arisen in regions adjacent
to the contemporary MTC of southwestern Australia.
The most straightforward approach to uncovering paleoclimates is from phys-
ical models that consider changes in earth system processes such as Antarctica's
glaciation and subsequent effects on ocean currents. The advantage of this
