elevations, while irrigation is necessary for agriculture on the
lowlands. The rainfall here comes largely from thunderstorms.

In South America the narrow Pacific slope has heavy rainfall (over 80
in.). East of the Andes the plains are dry (mostly less than 10 in.).
The southern part of the continent is very narrow, and is open to the
east, as well as more open to the west owing to the decreasing height of
the mountains. Hence the rainfall increases somewhat to the south,
coming in connexion with passing cyclones. Tasmania and New Zealand have
most rain on their western slopes.

[Illustration: FIG. 13.--Annual March of Cloudiness: Temperate Zones. E,
Central Europe; A, Eastern Asia; M, mountain.]

In a typical continental climate the winter, except for radiation fogs,
is very clear, and the summer the cloudiest season, as is well shown in
the accompanying curve for eastern Asia (A, fig. 13). In a more moderate
continental climate, such as that of central Europe (E, fig. 13), and
much of the United States, the winter is the cloudiest season. In the
first case the mean cloudiness is small; in the second there is a good
deal of cloud all the year round.

_East Coasts._--The prevailing winds carry the continental climates of
the interiors off over the eastern coasts of the temperate zone lands,
and even for some distance on to the adjacent oceans. The east coasts
therefore have continental climates, with modifications resulting from
the presence of the oceans to leeward, and are necessarily separated
from the west coasts, with which they have little in common. On the west
coasts of the north temperate lands the isotherms are far apart. On the
east coasts they are crowded together. The east coasts share with the
interiors large annual and cyclonic ranges of temperature. A glance at
the isothermal maps of the world will show at once how favoured, because
of its position to leeward of the warm North Atlantic waters, is western
Europe as compared with eastern North America. A similar contrast, less
marked, is seen in eastern Asia and western North America. In eastern
Asia there is some protection, by the coast mountains, against the
extreme cold of the interior, but in North America there is no such
barrier, and severe cold winds sweep across the Atlantic coast states,
even far to the south. Owing to the prevailing offshore winds, the
oceans to leeward have relatively little effect.

As already noted, the rainfall incr