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, . ~~1'),,)Q ~',.,;-' r,.> '<.o!, ~J.J CHRONOLOGY OF THE 1976-77 DROUGHT 29 According to his index, drought conditions 1976. Single very dry years occurred in existed 32 percent of the time, and extreme Missouri in 1901 and 1947, but usually dry, or drought occurred 6 percent of the time. The wet, years occurred in groups. most extreme conditions occurred during the The Governor's task force in Wisconsin 15-month drought from June 1933 to August studied precipitation records at five locations 1934 when his index dropped to -6; but the in the State where records started in the longest drought period was 36 months from 1870's or 1880's (Upper Mississippi River Basin June 1955 to May 1958. The second lowest Commission, 1977). Precipitation was below index value, -5.5, occurred during the latter 85 percent of normal at one or two locations in drought, but 16 of the 36 months were classed many years; but in only 6 years, 1895, 1910, as extreme drought; whereas, only 5 of the 15 1939, 1948, 1958, and 1976 was a drought months of the earlier drought were classed as almost statewide. About half the years since extreme. The Palmer index values are signifi- 1890 were below normal in some part of the cantly higher than the value of -8 computed State, and only three periods since 1871, 1876- for the drought in 1976-77 (fig. 7b) which indi- 84, 1902-07, and 1968-75, had no years with cates that conditions in 1976-77 were worse less than 85 percent of normal precipitation. than during the earlier droughts. These records prove that meteorological Palmer also computed his index for six droughts are fairly common occurrences in counties in the Sour is River basin in north- parts of Wisconsin, and even statewide western North Dakota between 1931 and 1962. droughts are not rare events. In this area, drought conditions existed 42 per- cent of the time, and extreme drought occur- red 7 percent of the time. The lowest index, -6.7, occurred during the 21-month drought from August 1933 to April 1935. This indi- cates that the drought of 1933-35 was more severe in this area than the drought of 1976-77 for which the minimum Palmer index was -5. The longest drought lasted 47 months from October 1955 to August 1959. The earlier drought had 12 months classed as extreme and the latter drought had just 4 months classed as extreme. October 1964 was very dry over both re- gions. There was no rain during the month near the eastern edge of Iowa near the Illinois- Wisconsin State line. An all time record for minimum monthly precipitation was set at Burlington, on the Mississippi River in south- eastern Iowa, where only 0.06 in. fell. Records for October were set at Moline, Peoria, and Cairo, Ill., where 0.01, 0.03 in. and a trace were recorded. Dubuque, Iowa, about 70 mi southwest of Madison, Wis., also recorded only a trace; whereas the average for the month is 2.74 in. New minimum temperature records for several days were set at Madison, Wis. The drought in Minnesota during 1976 was ranked as one of the four worst droughts since precipitation records began in 1891 (Upper Mississippi River Basin Commission, 1977). In 1910 the worst drought was in the southeast, in the northeast in 1934, in the northwest in 1936, and in the west-central and southwest in Precipitation and Runoff Annual precipitation in 1975 was above normal over both regions except for a band roughly 150 mi wide with its axis running from Green Bay, Wis. to Kansas City, Mo. in which precipitation was between 75 and 100 percent of normal. Precipitation in January and February 1976 varied radically in both time and space from less than 50 percent to more than 200 percent of normal. Above normal precipitation occur- red in March with more than twice normal in several areas. The above normal pattern con- tinued in April except for central and north- eastern Minnesota where precipitation was less than 50 percent of normal. Much below normal conditions spread to North Dakota, Iowa, and Wisconsin in May 1976 and into il- linois and Missouri in June. Rainfall in July in North Dakota was less than 25 percent of normal. The pattern of deficient rainfall con- tinually shifted and lasted through December 1976. A critical factor was the distribution of rainfall during the growing season as exempli- fied by data from Minnesota. The rainfall deficiency during April-August 1976 ranged from 2 in. in the north to 12 in. near the head- waters of the Minnesota River. Corn produc- tion was less than 20 bushels per acre where rainfall was less than 5 in. to more than 90 bushels per acre where rHinfall exceeded 11 in.