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III ~l" '!f~ .. U~....':,.J'4j,Iria HISTORICAL SETTING HISTORICAL SETTING 3 The 1976-77 drought in the United States affected a larger part of the country more se- verely than other droughts in the 20th century. Yet archaeologic and tree-ring evidence indi- cate that, meterologically and hydrologically at least, droughts in the past have been more severe and have lasted longer than the 1976-77 drought. In southern California, tree rings for the past 560 years show dry periods ranging from 6 to 40 years (Troxell, 1957) and periods that are predominantly wet last, on the ave- rage, 12.5 years, and those that are predomi- nantly dry last about 14.5 years (Thomas and others, 1963e). An extended drought occurred in the South- west from about 1276 to 1300. It is considered to be one of the prime reasons leading to the abandonment of the cliff dwellings and other community sites of several Indian groups in New Mexico and Arizona. The more notable droughts in the 20th cen- tury are: 1910 1924-34 1930-40 drought in the Great Plains drought in California drought in Oklahoma and the Midwest (the Dust Bowl) drought in the Southwest drought in the Midcontinent drought in the Northeastern States 1942-56 1952-56 1961-67 In 1910, the Dakotas, Nebraska, Kansas, and Oklahoma were hit by a drought. Precipi- tation in the Great Plains area was 71 percent of normal (Hoyt, 1938), but the area affected was large. Hoyt ranked the drought of 1910 as the third worst in semiarid States and as the seventh worst in humid States among the 15 worst droughts between 1880 and 1936. The period 1924-34 in California was pre- dominantly dry. This drought acted as a cata- lyst in the development of the State Water Plan and the Central Valley Project. The drought started abruptly in 1924, which was the driest year on record in the State until 1977. Runoff values for 1924 or for all or parts of the period 1924-34 were used as an- nual or multiyear criteria for the design of projects that required carry-over storage to provide firm low flows. The "Dust Bowl" that resulted from the drought of 1930-40 in western Oklahoma, par- ticularly in the Panhandle, and in eastern Colorado, and surrounding States is probably the drought that many people think of when a drought is mentioned. Now that the old-timers who lived through those days are not so numer- ous, the drought of 1976-77 may take its place as a conversation piece. Precipitation in Okla- homa was below normal in 7 of the 11 years, but only 3 of them had less than 85 percent of normal. The cumulative departure from the average for the 11 years was -19.79 in. which is almost the amount of rain that might be ex- pected in 8 months, on the average. Nearly half the Great Plains area had a desert climate in 1934 that produced arid and semiarid conditions in places that are normally subhumid. Seven weather observers in Okla- homa reported no rainfall during a calendar month in the sum mer of 1934, and rainfall was less than 0.25 in. at about 25 locations in Kan- sas. The deficient rainfall during the growing season from April through October was bad enough, but the area was the hottest in more than 40 years. High temperature records were set for June or July or for the April-August period. ~onthly temperatures ranged from 2.50 to 4.5 F above normal, and new daily high temperatures occurred at many places. Winds were frequent and strong enough to cause wind damage to structures. During the previous decade, rainfall had been above average and sufficient to encour- age farmers to plow up and plant land that was marginal without an ample water supply. With the cover of grass removed, the combination of deficient rainfall, the hot summer, and the wind easily converted the area into the "Dust Bowl." The parched soil was blown into drifts that buried what crops managed to sprout and made life miserable for the residents. About 50 million acres was affected at the height of the drought. It was this drought that caused an exodus from the farms in the stricken area and that was the impetus for soil conservation programs and better farming methods. An interesting perspective on the "Dust Bowl" is that though it was certainly dusty, there have been more recent periods of drought in Oklahoma that meterologically and hydrologically were more severe. Precipita- tion in 1956 in Oklahoma, New Mexico, and Kansas was 35 percent of normal, and the ave- rage flow of the Washita River near Durwood,