Part 3 (1/2)

In the western highland region of the United States considerable areas already have been made productive by irrigation, and it is estimated that about two million acres of barren land can be reclaimed by impounding the waters of the various streams now running to waste.

The distribution of rain with respect to the season in which it falls is quite as important as its distribution with respect to quant.i.ty. In tropical regions the ocean winds, and therefore the rainfall, come from the east. The eastern slopes of such regions, therefore, have a season in which rains may be expected daily, and another in which no rain falls for several months. In the temperate zones seasonal rains for a similar reason are on the western coasts.

Thus on the Pacific coast of the United States the rainfall varies from about one hundred inches in southern Alaska to about twelve in San Diego, Cal. Practically all the rain falls between October and the following May; very little or none falls in the interval between May and October. As a result, ordinary turf-gra.s.s, which will not withstand long droughts, grows in only a few localities of the Pacific slope. It is replaced by hardier gra.s.ses whose roots, instead of forming turf, grow very deep in the soil.

Common clover will not grow in this region unless irrigated; it is replaced by burr-clover, a variety of the plant that will not thrive in moist regions. Now the quality of the merino wool clip of California depends in no slight degree upon the burr-clover and other food-products that thrive in regions of seasonal rains; that is, a great commercial industry exists because of this feature of rainfall, and it could not long survive in spite of it.

[Ill.u.s.tration: CLIMATICALLY ADAPTED TO CULTIVATION--THE LOWLANDS PRODUCE BREAD-STUFFS AND FRUIT; THE MOUNTAIN-SLOPES ARE GRAZING REGIONS]

The seasonal rainfall also affects other agricultural industries. The sacked wheat-crop may be left in the field without cover or protection until the time is convenient for s.h.i.+pping it. The absence of summer rains makes possible in California what would be out of question in the Mississippi Valley, where a rainstorm may be expected every few days.

The quality of certain fruits depends largely on the season during which the rainfall occurs. Apples, pears, and grapes grown in regions having dry summers have usually a very superior flavor. The raisin-making industry of California also depends on the same condition, because, in order to insure a good quality of the product, the bunches of grapes, after picking, must be dried on the ground. To a certain extent this is also true of other fruits, such as dates, figs, and prunes, which frequently are sun-dried.

The presence of large bodies of water, which both absorb and give out their heat very slowly, tempers the climate of the nearby land and to that extent modifies the commerce of such districts. The grape-growing industry of central New York is a great one and its product is famous.

Its existence depends almost wholly upon the lake-tempered climate.

Elsewhere in the State the industry is on a precarious basis, and the product is inferior.

=Effects of Inclination of the Earth's Axis.=--The inclination and self-parallelism of the earth's axis is undoubtedly a very important factor in climate. Practically it more than doubles the width of the belts of ordinary food-stuffs by lengthening the summer day in the temperate zone. Beyond the tropics the obliquity of the sun's rays are more than balanced by the increased length of time in which they fall.

Thus, in the lat.i.tude of St. Paul, the longest day is about fifteen and one-half hours long; at Liverpool it is nearly seventeen hours long; a greater number of heat units therefore are received in these lat.i.tudes during summer than are received in equatorial regions during the twelve-hour day. Moreover, the summer temperature is higher in these lat.i.tudes than in the torrid zone, because the sun is s.h.i.+ning upon them for a greater length of time.

The result of these various influences is far-reaching. Because of the long summer days and short nights, wheat can be cultivated to the sixtieth parallel. Corn, which gets scarcely enough warmth and light in the torrid zone to become a prolific crop, attains its greatest yield in the lat.i.tude of fourteen-hour days.

These factors, it is evident, carry the grain and meat industries into regions that otherwise would not be habitable. Because the long summer days produce these great food-crops, commerce and its allied industries have reached their maximum development in these regions. Human activities are greatest in the zones bounded by the thirty-fifth and fifty-fifth parallels, the zone that includes the greater parts of the United States, Europe, China, j.a.pan. They are greatest, moreover, because of their geographical position.

QUESTIONS FOR DISCUSSION

What would be the probable effect on the food-crops of the United States were the main body of the country moved twenty degrees north in lat.i.tude? Which would then be the wheat-growing States, the cotton-producing States?

Ill.u.s.trate the connection between occupation and alt.i.tude above sea-level.

What difference would it make to the corn-crop were the days and nights always twelve hours long?

What would be requisite to make Canada a centre of silk production?

Why is not cod-fis.h.i.+ng an industry off the east coast of Florida?

Why is the greater part of the Russian Empire destined to be spa.r.s.ely peopled?

FOR COLLATERAL REFERENCE

A rain chart of the world.

A chart of isothermal lines.

CHAPTER V