Rainfall and Population.

New Zealand Graphic, Volume XLVII, Issue 5, 31 January 1912, Page 41

Rainfall and Population.

Dr VV. J. McGee, in examining the widelydiffering estimates of the ultimate population of the United States—which the latest computer, Henry Gannett, puts at 250,000,000 ninety years hence—points out that a practical limit to the productivity and habituality of a country is fixed by limitation in its water supply. In arid lands like Egypt careful calculations have been made of the amount of ■water necessary to make land productive. An acre requires so many inches of water a year. Het us say 30, before it will raise enough vegetable food to keep one person. Thirty inches is under the mark, because man does not live by bread alone, but on meat, and the animals which give him that have also to be sustained by vegetable food. The man who eats 2001 b of bread, and 2001 b of beef a year, and drinks in the same time a ton of water, and the equivalent of 400 tons of water which have gone to make the bread, and 4000 tons of water which have gone to rear the beef—44oo tons of water in all. Consequently, the water supply of a country in which man is to live must always be equal to something over 4000 tons per individual. The annual rainfall of the countries of the northern hemisphere is about 30 inches, only half enough to fertilise one acre to a sufficient extent to keep a man. Roundly speaking, perhaps, one might say that the world’s water supply is sufficient to keep a population of one man to every two acres.