Dry-farm area of the world

Dry-farming is a world problem.  Aridity is a condition met and to be overcome upon every continent.  McColl estimates that in Australia, which is somewhat larger than the continental United States of America, only one third of the whole surface receives above 20 inches of rainfall annually; one third receives from 10 to 20 inches, and one third receives less than lO inches.  That is, about 1,267,000,000 acres in Australia are subject to reclamation by dry-farming methods.  This condition is not far from that which prevails in the United States, and is representative of every continent of the world.  The following table gives the proportions of the earth’s land surface under various degrees of annual precipitations:—­

Annual Precipitation Proportion of Earth’s Land Surface
Under 10 inches 25.0 per cent
From 10 to 20 inches 30.0 per cent
From 20 to 40 inches 20.0 per cent
From 40 to 60 inches 11.0 per cent
From 60 to 80 inches 9.0 per cent
From 100 to 120 inches 4.0 per cent
From 120 to 160 inches 0.5 per cent
Above 160 inches 0.5 per cent
Total 100 per cent

Fifty-five per cent, or more than one half of the total land surface of the earth, receives an annual precipitation of less than 20 inches, and must be reclaimed, if at all, by dry-farming.  At least 10 per cent more receives from 20 to 30 inches under conditions that make dry-farming methods necessary.  A total of about 65 per cent of the earth’s land surface is, therefore, directly interested in dry-farming.  With the future perfected development of irrigation systems and practices, not more than 10 per cent will be reclaimed by irrigation.  Dry-farming is truly a problem to challenge the attention of the race.

CHAPTER IV

DRY-FARM AREAS.—­GENERAL CLIMATIC FEATURES

The dry-farm territory of the United States stretches from the Pacific seaboard to the 96th parallel of longitude, and from the Canadian to the Mexican boundary, making a total area of nearly 1,800,000 square miles.  This immense territory is far from being a vast level plain.  On the extreme east is the Great Plains region of the Mississippi Valley which is a comparatively uniform country of rolling hills, but no mountains.  At a point about one third of the whole distance westward the whole land is lifted skyward by the Rocky Mountains, which cross the country from south to northwest.  Here are innumerable peaks, canons, high table-lands, roaring torrents, and quiet mountain valleys.  West of the Rockies is the great depression known as the Great Basin, which has no outlet to the ocean.  It is essentially a gigantic level lake floor traversed in many directions by mountain ranges that are offshoots from the backbone of the Rockies.  South of the Great Basin are the high plateaus, into which many great chasms are cut, the best known and largest of