Regional amount of precipitation, over many portions of the habi table earth, has been observed for long periods substantially as follows : In the polar regions there is no rainfall. Precipitation there is con gealed in snow and icy particles. In the tropics there is little snow except on the highest moun tains and most precipitation is in the form of rain. In the upper latitudes of the temperate zones there are both rain and snow. Over the Sahara, Arabia and other desert regions and in the desert regions in Australia and South America there is but little precipitation, while along windward coastal regions the annual precipitation is abundant, as found along the Atlantic and other continental coasts facing eastward. Usually those sides of mountain ranges that face oceans, or large bodies of water, have a much larger rainfall than do the opposite sides, which face inland areas, There is more rainfall on the slopes of the 'Sierra and Coast ranges where many glacial lakes and ponds exist in the ranges themselves, such as Tahoe, Clear Lake and others, there is rainfall on their eastern East of some of these and of the Mountains the annual precipitation is light and large desert areas had existed, but for irrigation. No one law has been deduced from all these varied phe nomena, affecting precipitation over all parts of the habitable globe to determine its amount. Much data has been collated from actual meas urements. Some of these will indicate the amount of in those regions and at various altitudes.
E. S. Bellasis, sometime engineer of the Pub lic Work in India, in substance stated that athe rainfall in India varied from 2 or 3 inches in Scinde to 450 inches at Cherrapunji in the eastern Himalayas and that at two sta tions in the Bombay hills, only 10 miles apart, the annual rainfall were respectively 300 inches and 50 inches and that in England at Hem stanton, it was about 20 inches, while at Seath waite it was about 200 He stated that athe annual rainfall at Mercara in South India was 119 inches, in King William's Town in Cape Colony 27 inches, at Melbury Moor, in England 50.7 inches, at Newport in the Isle of Wight 32 inches, in the basin of the Cataract River in New South Wales from 33.7 inches, in 1896, to 56.4 inches, in 1898 in the basin of the Nepean River in New South Wales 44.3 inches and in 1905 in the valley of Sudbury, Mass., 42.3 inches.) The water supply of a country is largely conditioned upon its water resources and the latter are dependent to a large extent upon its rainfall, or rather precipitation, which includes rain, hail, sleet and snow. The amount of annual precipitation over a given territory in successive years is not constant, nor is it uni formly distributed, except over a few such States as Wisconsin and Michigan, and over some foreign limited districts.
The annual precipitation in the State of Washington ranges from 12 to 120 inches in different localities, though in Seattle for a period of 19 years it averaged 38.8 inches.
In different parts of Oregon it ranged from 8 to 138 inches and in Texas from 9.3 inches at Pasco to 48.2 inches at Houston. Nor is the annual precipitation over a locality constant from year to year. The Weather Bureau's report shows that theprecipitation at Dodge City, Kan., has ranged from 9.9 to 33.7 inches. There are dry and wet years as there are dry and wet seasons. In the drought of 1894 and 1895. the deficiency in precipitation measured in the upper Mississippi Valley from 7.8 to 12 inches, in New England from 5.3 to 8.1 inches and in the south Pacific watershed from 4.4 to 4.6 inches. In three months of 1905, there was an excess of 2 inches in the rainfall at Yuma over its mean annual precipitation. In 1900, the rainfall at Bay Saint Louis, Miss., was 101.5 'inches which was an excess of about 50 inches over normal precipitation for the State. The difference between the maximum and mini mum rainfall on the Croton watershed (New York) in a period of 43 years was 26.8 inches and in Pittsburgh (Pa.) that difference was 25.3 inches in a period of 71 years.
Mean Annual Precipitation in the United States and Canada.- The United States main tains several hundred observation stations in addition to those maintained by the States them selves and by individual and corporate enter prise, where meteorological and climatological observations are made and for half a century have been made and records kept of the annual precipitation at those stations. From all such official and authentic observations and the com putations made therefrom, climatological tables have been compiled, showing in most cases over periods of years the mean annual precipitation at scores of stations in the United States. Foreign countries have made similar observa tions and records. In nearly all of the tables, the measurements are the resultant of many observations and are denominated athe mean annual precipitation?) From such official and from other well-au thenticated measurements, the writer has sr lected some and averaged others from approved records to ascertain and state the mean annual precipitation over the United States and Canada. The following represent the mean annual pre cipitation over the localities mentioned, or they are aggregated from a number of stations over large areas, showing such precipitation. Many of these are from the reports of the United States Weather Bureau, extending over a num ber of years and others from authentic data. The mean annual precipitation in the coastal region of Alaska varies from 60 to 110 inches.
United States.- The greatest annual pre cipitation in the United States is over the west ern slopes of the mountains forming the Con tinental Divide which intercept the vapor-laden clouds from the Pacific and precipitate their moisture in some localities to an average of 70 to 135 inches.