Discuss in detail the regional and seasonal distribution of precipitation in the world.
Answers
Explanation:
Much has been written on the subject of precipitation in the United States, and a number of charts have been prepared and published showing its geographic distribution. Most of these, however, have represented the average annual amount, the only other available chart, where more than a very limited number of records were used, being that for the summer-half year.
The need for a series of charts based on all available records, showing the seasonal distribution of precipitation in this country has long been recognized, and the accompanying series is presented to meet this need. Those here shown consist of 12 monthly charts, and 1 for each of the 4 seasons, together with auxiliary maps for the seasons showing the percentage of the annual precipitation that occurs in each. The monthly and seasonal charts are based on all available records of sufficient Length for such use, about 3,600 in number, reduced to a uniform 20-year period.
There are, in addition, a number of graphs showing for selected stations representing various rainfall types, the total precipitation in each season for each of the 20 years on which the maps are based. These show the relative variations in amount that may be expected from year to year in different sections of the country, and also give an indication of the dependability of the averages. In localities where the dispersions about the mean value are small, the latter is more indicative of the amount likely to he received in a particular year than in those where wide variations are shown by the graphs.
Departures from year to year from the average precipitation vary in magnitude inversely with the length of the season considered. The relative variations from the mean for the annual, the summer-half year, each of the 4 seasons, and for each of the 12 months, are graphically shown in figure 1, in such manner as to admit of direct comparison, as the scales are drawn on a comparable basis.
In addition to an indication of the variations from the mean precipitation that are likely to occur, it is important in considering the representations of precipitation charts to take into account the frequency with which significant amounts occur, the intensity of falls, and the subnormal frequency and duration. Auxiliary charts for use in this connection are presented as follows: Showing the average number of days annually with precipitation from 0.01 inch to 0.25 inch in 24 hours; the average number of days annually with 0.26 to 1 inch; the average annual number with more than 2 inches; the average annual number with more than 1 inch in an hour, and the maximum precipitation in 24 hours for the entire 20-year period. Also. the percentage of years east of the Rocky Mountains with 30 consecutive days or more, without 0.25 inch of rainfall in 24 hours from March to September, inclusive, and the greatest number of consecutive days without 0.25 inch in 24 hours for the same months. These auxiliary charts are based on the records of all regular reporting stations for the 20-year period from 1895 to 1914.