ual in Europe, as was the change in
temperature, but more sudden in North America. The curves for central
Europe and for northern Asia illustrate these continental summer rains
(see fig. 12). The summer maximum becomes more marked with the
increasing continental character of the climate. There is also a
well-marked decrease in the amount of rainfall inland. In western Europe
the rainfall averages 20 to 30 in., with much larger amounts (reaching
80-100 in. and even more) on the bold west coasts, as in the British
Isles and Scandinavia, where the moist Atlantic winds are deflected
upwards, and also locally on mountain ranges, as on the Alps. There are
small rainfalls (below 20 in.) in eastern Scandinavia and on the Iberian
peninsula. Eastern Europe has generally less than 20 in., western
Siberia about 15 in., and eastern Siberia about 10 in. In the southern
part of the great overgrown continent of Asia an extended region of
steppes and deserts, too far from the sea to receive sufficient
precipitation, shut in, furthermore, by mountains, controlled in summer
by drying northerly winds, receives less than 10 in. a year, and in
places less than 5 in. In this interior district of Asia population is
inevitably small and suffers under a condition of hopeless aridity.

The North American interior has more favourable rainfall conditions than
Asia, because the former continent is not overgrown. The heavy rainfalls
on the western slopes of the Pacific coast mountains correspond, in a
general way, with those on the west coast of Europe, although they are
heavier (over 100 in. at a maximum). The close proximity of the
mountains to the Pacific, however, involves a much more rapid decrease
of rainfall inland than is the case in Europe, as may be seen by
comparing the isohyetal lines[5] in the two cases. A considerable
interior region is left with deficient rainfall (less than 10 in.) in
the south-west. The eastern portion of the continent is freely open to
the Atlantic and the Gulf of Mexico, so that moist cyclonic winds have
access, and rainfalls of over 20 in. are found everywhere east of the
100th meridian. These conditions are much more favourable than those in
eastern Asia. The greater part of the interior of North America has the
usual warm-season rains. In the interior basin, between the Rocky and
Sierra Nevada mountains, the higher plateaus and mountains receive much
more rain than the desert lowlands. Forests grow on the higher