The Seasons of the Desert Belt.—The third type of rainfall, calms in our diagram, is that of the desert belts 25 to 30° from the equator. When the sun's rays are vertical near the equator these latitudes in both hemispheres lie in the belt of subtropical high pressure or else on the borders of the trade winds. Hence they re ceive no rain. They are warm, or more often hot, at these times, because the sun's rays are only slightly oblique, and the sky is un clouded. In January the climatic belts swing so far south that the northern desert belt may be touched by the edge of the westerlies, and hence occasionally receives a little rain. At the same time the southern desert belt is touched by the edges of the equatorial rainbelt. Thus the desert belts have two brief periods of slight rain. This gives four seasons, (1) a slightly rainy winter with pleasant tem peratures, (2) a hot, dry spring or "fore-summer," (3) a hot summer with a little rain, and (4) a dry, hot autumn, or "after-summer." Southern Arizona and central Arabia are good examples of this type.
Why Subtropical Regions Have One Wet and One Dry Season.— In the next diagrams we come to the subtropical regions. Here in latitudes 30 to the belt of high pressure and aridity rules during the summer of each hemisphere, while in winter the belt of westerlies swings equatorward and gives rain from frequent cyclonic storms. Notice how the curves for the two hemispheres in this and all other cases are really the same except that the seasons are six months different. Thus the subtropical rains of the northern winter in Jan uary correspond to the rains of the southern winter in July. Cali fornia and such Mediterranean countries as southern Italy, Greece, and Palestine are good examples of the subtropical type in the north ern hemisphere, while Cape Colony and central Chile are of the same kind in the southern hemisphere.
The Seasons of Temperate Regions.—The next diagrams represent the fortunate temperate regions where westerly winds and cyclonic storms prevail, and there is plenty of precipitation, that is, either rain or snow, at all seasons. There the seasons depend upon changes of temperature and not of rainfall. The northern and eastern United States and western Europe, together with Japan and New Zealand, are the chief examples of this type. The people who live there are always talking about the weather because it keeps changing. This is quite unlike the dry belts, where little is said about the weather, because it is almost always clear. There the water supply is one of r the chief subjects of conversation. The abundance of water at all seasons in regions of cyclonic storms makes it possible for farmers to live everywhere. People do not have to be crowded into compact villages near the central water supply as they do in dry countries. They live where they choose, even though it be miles from neighbors. This has helped to make the people of such regions more resourceful and better able to take care of themselves than are those of other parts of the world.
Even Distribution of Polar Precipitation.—Finally well toward the poles we find precipitation throughout the year, but chiefly in summer, as may be seen in Fig. 70. The amount is small because cold air cannot hold much moisture.
With certain modifications due to the continents and their relief the rainfall of any part of the world belongs to one of the types shown in Fig. 70. When these types are understood one can easily judge of the probable nature of the seasons in any part of the world. Thus one can appreciate the effect which the seasons are likely to have upon farming and other industries about which he reads, and also upon his own pleasure if he travels in distant regions.