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M.T.K. Arroyo et al.
the Andean mountains , and the cool equatorward-running Humboldt
current. South of 30°S, the South Pacific High is displaced to around 39°
to 40°S over summer months , determining a mediterranean-type climate
with prolonged summer drought north of around 39° to 40°S. The
Humboldt current maintains cool conditions along the entire Pacific coast,
leading to humid and foggy conditions especially in coastal locations .
Along this gradient, total precipitation increases from around 1500mm at
latitude 39°S to close to 4500mm in coastal areas at latitude 47°S. Inland
from 45° to 55°S, precipitation is much lower (Figure 8.1a). In the
extreme southwest, precipitation can be around 1300mm to 1400mm
(Figure 8.1a). Mean summer and winter temperature conditions along the
southern Pacific have been well documented by Alaback (1991), who
showed that greater summer warmth is seen in relation to the Pacific
Northwest coast. Mean annual temperature trends, are shown Figure
8.1b.
A striking feature of the general rainforest region that Alaback (1991)
failed to mention in his comparison of rainforest climates is high climatic
equability . Figure 8.2a shows that the annual temperature range for
coastal stations in South America rarely exceeds 7°C. Using the mean
maximum of the warmest month and the mean minimum of the coldest
month (Figure 8.2c), the temperature range is still low-not exceeding
20°C. More interestingly , there is no increase in annual temperature
range along the entire Pacific coast in southern South America. There are
few data for inland locations in the general rainforest area . Lonquimay
(38°26'S, 900m) has an annual temperature range of 13.2°C. The corresponding value to Balmaceda (45°54' S, 520m) , which is farther to the
east than the rainforest area , is 12.1°C, suggesting that temperature
moderation is characteristic of the rainforest zone in general. This
tendency derives from the tapering southern South America landmass,
leading to a decreased land/ocean ratio with latitude . A fairly low annual
temperature range also characterizes mediterranean-type climate latitudes
and the seasonal rainforest area in western North America (Figure 8.2b,d).
However, as the perhumid and boreal rainforest regions are approached,
equability diminishes, on account of an expanding land/ocean ratio. Bailey
(1964) developed a nomogram that expresses equability in relation to a
mean annual earth temperature of 14°C. The equability rating of all
South America cool temperate rainforest types falls in the 50% to 70%
range , which comes very close to areas in southeastern Brazil and northern
Australia as illustrated by Axelrod (1992) (Figure 8.3). The corresponding
equability ratings for the seasonal and perhumid rainforest areas of
western North America overlap with those of southern South America.
However, that of the boreal rainforest is considerably lower (40%).
The South American temperate rainforest zone thus exhibits not only
a warmer winter temperature, but greater overall regional uniformity in terms of temperature extreme s than its North American
counterpart.
M.T.K. Arroyo et al.
the Andean mountains , and the cool equatorward-running Humboldt
current. South of 30°S, the South Pacific High is displaced to around 39°
to 40°S over summer months , determining a mediterranean-type climate
with prolonged summer drought north of around 39° to 40°S. The
Humboldt current maintains cool conditions along the entire Pacific coast,
leading to humid and foggy conditions especially in coastal locations .
Along this gradient, total precipitation increases from around 1500mm at
latitude 39°S to close to 4500mm in coastal areas at latitude 47°S. Inland
from 45° to 55°S, precipitation is much lower (Figure 8.1a). In the
extreme southwest, precipitation can be around 1300mm to 1400mm
(Figure 8.1a). Mean summer and winter temperature conditions along the
southern Pacific have been well documented by Alaback (1991), who
showed that greater summer warmth is seen in relation to the Pacific
Northwest coast. Mean annual temperature trends, are shown Figure
8.1b.
A striking feature of the general rainforest region that Alaback (1991)
failed to mention in his comparison of rainforest climates is high climatic
equability . Figure 8.2a shows that the annual temperature range for
coastal stations in South America rarely exceeds 7°C. Using the mean
maximum of the warmest month and the mean minimum of the coldest
month (Figure 8.2c), the temperature range is still low-not exceeding
20°C. More interestingly , there is no increase in annual temperature
range along the entire Pacific coast in southern South America. There are
few data for inland locations in the general rainforest area . Lonquimay
(38°26'S, 900m) has an annual temperature range of 13.2°C. The corresponding value to Balmaceda (45°54' S, 520m) , which is farther to the
east than the rainforest area , is 12.1°C, suggesting that temperature
moderation is characteristic of the rainforest zone in general. This
tendency derives from the tapering southern South America landmass,
leading to a decreased land/ocean ratio with latitude . A fairly low annual
temperature range also characterizes mediterranean-type climate latitudes
and the seasonal rainforest area in western North America (Figure 8.2b,d).
However, as the perhumid and boreal rainforest regions are approached,
equability diminishes, on account of an expanding land/ocean ratio. Bailey
(1964) developed a nomogram that expresses equability in relation to a
mean annual earth temperature of 14°C. The equability rating of all
South America cool temperate rainforest types falls in the 50% to 70%
range , which comes very close to areas in southeastern Brazil and northern
Australia as illustrated by Axelrod (1992) (Figure 8.3). The corresponding
equability ratings for the seasonal and perhumid rainforest areas of
western North America overlap with those of southern South America.
However, that of the boreal rainforest is considerably lower (40%).
The South American temperate rainforest zone thus exhibits not only
a warmer winter temperature, but greater overall regional uniformity in terms of temperature extreme s than its North American
counterpart.