Evening Star Newspaper, September 14, 1930, Page 96

SUNDAY STAR, WASHINGTON, D. C, SEPTEMBER 14, 1930. ENIGMA of the Great DROUGH'T W hen warm moisture-laden air ascends to a high altitude it expands, cools, be- comes saturated and is forced to per cipitate some of its water vapor as rain. “The second way to get the warm air up is to have a mountain chain, up the sides of which Errant Behavior of Arctic Air Currents, HE Summer of 1920 will long be re- membered as a “humdinger,” when heat over half the United States was violent and continuous, when our fields and lawns lay parched, when crops were burned up, when forest fires raged and cattle thirsted for water. When the area affected by the drought, its jength in months and deficiencies in precipi- tation are considered, it becomes the greatest drought in the climatological history of the country. An official report characterizes it thus: “Up to August 1 the deficiencies in rainfall in gen- eral has extended over a period of eight months in Maryland, Virginia and West Virginia; five months in Kentucky, Ohio, Indiana, Illinois and Missouri, and two months in Tennessee, Arkansas, Texas and Oklahoma. The enormity of the deficiency in water from that normally received in the form of rain for these 12 States for tk~ iaonths named is shown by a calcula- tion . at the actual shortage exceeds 300,000,- 000,000 tons of water.” It didn’t rain becauseé air currents which ordinarily flow down the central part of the country became wayward and gay. They un- expectedly took a Summer jaunt over Europe and parts of Asia—just why nobody knows. Heat and drought tend to perpetuate them- selves from day to day and from week to week, according to officials of the United States ‘Weath: ~ Bureau. But a drought such as that of 1930 is a much more serious thing than the more violent mani- festations of Nature. It means more than immediate discomfort and inconvenience. It has long and far-reaching consequences which will possibly affect our national life for several years. IN geographical area, the drought extended over more than half of the United States; broadly speaking, from the Atlantic seaboard to the Rocky Mountains. That means that the great corn and wheat growing regions of the country were affected. During the early part of the Summer New England did not suf- fer particularly, but during August the drought spread out its parching and burning fingers to close down on the picturesque New England hillsides and over New York and Michigan. For once in recent years Florida has_had a real “break.” There has been enough rainfall from North Carolina southward through Ala- bama to the Gulf Coast to keep that area from feeling the. worst effects of the drying and parching air. The region around the Western Great Lakes was saved by local conditions, too, but in general the broad expanse of country from* Texas. and Colorado eastward through Kentucky, Indiana, Ohio, Illinois, Missouri, Ar- kansas, Oklahoma to the Atlantic seaboard throvgh Virginia and Maryland and Pennsyl- vania has borne the brunt of the worst drought in the history of the country. “What was the cause of this devastuting drought?” the one man in Washington who probzbly knows most about the whys and whercfores of weather all over the world was asked, Dr. W. J. Humphreys, meteorologist - physicist of the United States Weather Bureau, smiled and gave the typical cautious answer of the scientist, “There wasn’t any one cause,” he said. “I can give you some causes and the causes of those causes, but finally we will reach a point where there will be a cause that we can’t ex- plain. “Bu¢ you know, of course, that rain falls be- tause of the water that got into the air as a re- sult of evaporation over both the land and the ocein. Water is evaporated from rivers and streams, from plants and from everything on tk- earth. When water vapor isn’t in the afr, W hich Normally Flow Down Into Missis- sippi Basin and Produce Rain by Cooling Moisture-Laden Breezes From the South, Largely Responsible for Parched Conditions of the United States This Summer. naturally there can’t be any considerable rain- fall. This Summer has been dry because there was little or no rainfall in the Spring. Since there was little rainfall in the Spring, there was little water to be evaporated, hence little to form clouds and none for Summer rains. ‘““The water supply upon which the parts of the country suffering from the drought are now dependent is, in small part, water which came down as rain a year or so ago. It is the reserve supply which fell some time ago and sank deep into the earth which is now feeding our wells, springs, streams and rivers. It took that water a long time to reach the sources from which it is now coming. “The supply furnished by the last rainfalls we had have been evaporated long ago. The first rain to fall upon the parched and thirsty earth will be immediately soaked up by thirsty plants, animals and people and evaporated into the dry atmosphere. Little or none of it will sink deep into the earth to replenish the supply which during the period of the drought has been gradually called upon to supply the fam- ishing earth. “Thereafter, for pbobably a year or two, there will be less of a reserve supply of water in the earth, less in our rivers and streams to evap- orate into clouds and, therefore, less for rain- fall. “That is a superficial reason for the drought of the Summer of 1930. We can go back of that.” He then explained the scientific cause of rainfall in general. As the water evaporates from land and sea and passes into the atmosphere, the tempera- ture of the atmosphere determines the amount of water vapor which can be held in suspension. The higher the temperature the larger the amount of water vapor the atmosphere can hold. This warm air must be cooled to a point where it becomes saturated with moisture before it will give up this vapor in the form of rain, There is only one effective method of cooling air in order to produce rainfall, and that is for it to travel to considerable heights. As it is pushed up high, it expands, because in the up- per reaches of the atmosphere the pressure is less, but it expands at the expense of its heat. When it becomes so cool that all its water vapor cannot be retained, we get clouds and rain. “But the point is,” Mr. Humphreys explained, “to get the warm, vapor-laden air up. There are three main ways in which this is done. First, by having the surface air strongly heated by the sun so that there is plenty of convec- tion. Then the cumulus clouds form and rain will fall. But this Summer the water wasn't at the surface of the earth because there had not been sufficient rains in the!Spring to furnish water for any considerable amount of water vapor. : Map room of the United States Weather Bureau, where data received from more than 200 stations are entered on charts to be studied by expert forecasters. it must travel in order to flow to the other side. Cooling takes place near the mountain tops. The Sierras, in California, the highest moun- tains in the United States, are responsible for a great deal of rainfall in the Summer and for heavy falls of snow in the Winter, the drifts sometimes piling as high as 40 feet. But there are no very high mountain chains in the East- ern or Central portions of the country to aid the process of precipitation. “The third way, and that which is most ef- fective in causing rainfall throughout the Cen- tral and Eastern parts of the United States, is brought about by air circulation. The warm, moist air from the tropics, more directly from the vicinity of the Gulf of Mexico and the Caribbean, moves along the line of least re- sistance up the broad Mississippi Valley region to meet the cooled air from the Arctic, which is moving southward down the central part of the country. “Naturally, where the two come together the warm, moist air rises as the cooler air sinks and a circulation is produced. This tendency is greatly increased by the rapid movement air caused by the rotation of west to east on its axis. The is lighter, would more easily east, while the cool, heavier to the west. Eitg i Sefis “THESE air currents behave and I might if we tried balance on a swiftly rotating tumble over themselves and The warm air slides up to becomes cold and releases its vapor as In this interchange of air currents, storms general and widespread develop. Local tions make the circulation of the current vigorous in onc place than in another, which in a measure determines the local character of certain rains. “During the average year Central Uni States and Canada are the happy hunting ground of the air currents that travel down EE@E&E H region. But this year the interchange of cold and equatorial air has been limited over the Central United States. The cold air has drained down from the Arctic over other parts of the world—over Europe, East China, Korea— and the rainfall has been exceptionally heavy in those places. The usual circulation of air around the United States has been absent. The stagnation best explains both the lence and the persistence of the drought. “Why it happened that way we do not ki Why those countries got the rainfall and we failed to receive our mormal supply may mnot be known for many years to come, when our knowledge of meteorology, weather conditions, air currents from the Arctic and Antarctic is much more comprehensive than it is today. “The heat we have had during the Summer of 1930 is a result of the drought. The drought is not the result of the heat. When a region has not been rained on, it heats up. As long as water is there the evaporation tends to cool it off, but if it is already dry it simply gets hotter. If you put a wooden bucket of water and a ball of metal out in the sunshine, the water ir the bucket will remain fairly cool because of the evaporation, but the metal gets hotter the longer the sun shines upon it. So it is with the surface of the earth. “That in a measure explains why it has been almost as hot in the Northern sections of the great central valley of the United States as it has been in the Southern parts. Where there have been local conditions which might cause some evaporation and cooling of the air, the showers have been local in character. If you bring a large block of ice into a warm room, some circulation of air is created in the immediate vicinity of the block of ice. The warm air from the far corners of the room does not rush over toward the ice block, how- ever. The same principle holds true with the circulation of air in the immediate vicinity of Continued on Fourteenth Page