Torrential Rains as a Serious Handicap in the South

Abstract

I N the South (the South-Central and South Atlantic States) rainfall has seldom been considered an outstanding environmental influence. One reason for this is that there is much less variation from year to year in the total yield of the cotton crop than of the crops of the semiarid and subhumid regions, where rainfall is obviously of critical importance. However, recently available evidence that soil erosion is especially serious in the South invites attention to its climatic basis. And here the comparative frequency of torrential rains is really startling. An analysis of the records of the rainfall totals in short periods for each of the 208 United States Weather Bureau stations with recording gauges was made by Yarnell.' He found that falls of half an inch in 5 minutes normally occur in half of the years in the South, or five times as often as in Wisconsin and Indiana. Nearly an inch falls in 5 minutes once in a century in all parts of the South, whereas such a heavy downpour is almost unknown in the North (the NorthCentral and Northeastern States). An inch of rain in IO minutes is received once in about 7 years in the South, or about eight times as often as in the North. Two inches in half an hour falls once in about 7 years in the South, or about ten times as often as in the North. Three inches in an hour falls once in a decade in the South; the North does not get such a rain once in a century. The South has a 3-inch rain in 2 hours once in about 5 years; the North, once in 50 years. Four inches of rain in 4 hours occurs once in about 5 years in the South, but only once in a century in the North. Five or 6 inches in 8 hours occurs once in a decade in the South, but less than once in a century in the North, much of which has never received more than 4.5 inches in 8 hours. The South has falls of about 8 inches in i6 hours about four times in a century; the North in a century has maxima of less than 6 inches. The amount of rainfall in 24 hours to be expected once in 5 years is about twice as great in the South as in the North. For storms of a severity that normally