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~ ~ ~~. t~ '",' '.;' J" !9 DROUGHT AND ITS RAMIFICATIONS 11 ;;;-7 ~ ~ . , ~ - oj 0 W ~ <;) ~ C '" Q) ~ ... m ~ ... 0 R ..., m '" Q) ~ m .<:: ~ ..., ~ ::l 0 '" ~ '" Q) ~ - .~ E M '" ~ M m .:I N Q) ~ Q) ~ ... 0 oj ~ ::l ~ ..., C oj 0 0 ~ ... ~ oj Q) C m .... 00 ~ Z .... M w I 00 '" ~ .... --- CD ~ .... 00 ~ - - Q) ~ 00 00 .5 ~ t- m t- oo I ~ 0 CD 0> . .... 00 ~ - Q) :> M Q) 00 - ~ ... Q) +-' N oj ~ ~ ... 0 :;; c ~ .S +-' oj 0 ::l +-' ~ <! ::l - 0 ~ 0 0 0 0 0 0 0 0 ~ ~ 00 0 . 00 ~ ffi 0 ~ M . . . 00 J.33::1 NI '3:)\1:l8nS ONV" or; MOl38 83.l\1M OJ. H.ld30 Q) ... ::l bD j:;:; between the actual precipitation and that required to meet the demands of evapo- transpiration is a fairly direct measure of the departure from normal. Palmer (1965) computed indexes for many droughts prior to 1963 mainly in Kansas and Iowa. He concluded that a value of -4 corre- sponds reasonably well with "extreme" drought, and the minimum value that he tabu- lated is -6.2 for September 1956 in western Kansas. Therefore, the values of -7 to -9 determined for the drought in 1977 are rare extremes. In fact, early editions of maps showing Palmer indexes in this range described the conditions as "Too dry to measure!" Figures 6 and 7 are a series of maps of the United States showing the isopleths of the Palmer index for selected dates in 1976 and 1977. As of May 1, 1976 (fig. 6a), the Palmer index indicated severe drought conditions only in California and western Virginia. By July 3, 1976 (fig. 6b), extreme drought conditions had developed in California and the eastern Dakotas-western Minnesota area. The severe drought in Virginia had eased, but eastern Maryland and Delaware were now affected as was northern New Mexico and much of Wiscon- sin. These same general areas shifted, changed shape, and enlarged by August 28, 1976 (fig. 6c). Early fall rains alleviated the drought conditions in all areas but the upper Midwest (fig. 6d). The lowest indexes computed in 1976 were -6 in California and -7 in South Dakota. By February 1, 1977 (fig. 7a), the Palmer index had dropped to -5 in three areas of Cali- fornia, Oregon, and Washington and to -7 near the middle of Minnesota and Wisconsin. In the next 3 months (fig. 7b), the index had dropped to -7 or -9 in parts of the Pacific Coast States, southeastern Idaho and in the Minnesota-Wis- consin area. Also an area covering parts of Colorado, Utah, and Wyoming became dry enough to develop indexes between -4 and -6. The July 2, 1977 map (fig. 7c) shows about the same indexes in the same general areas though the index dropped to -8 in central California. By October 29, 1977 (fig. 7d), the area west of the Great Lakes changed from severe drought conditions to normal or even moderately wet; whereas, the drought lingered in a large part of the 11 western states though the minimum drought index was now -6. Shortly after the last map was prepared, rains came to most of