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!\1'r'l<!l"l l~ :) ,~.;; Ii GENERAL EFFECTS OF DROUGHT ON WATER RESOURCES B3 sources is"likely to pass through the soil before doing so, Most of the precipitation in the Southwest gets only as far as the soil zone and then returns to the atmosphere; only a small proportion of it becomes ground water or surface water. Satisfactory techniques for measuring and recording fluctuations in the volume of soil water have not been developed for areas larger than small experimental plots. Thus, by contrast with fluctuations in amount of ground water and especially of surface water, quan- titative data concerning soil water are practically non- existent. Qualitative data on the effects of drought upon soil water are based for the most part upon the effects upon the vegetation whose supply of soil water is derived directly from precipitation. A description by Bonnen and Ward (1956, p, 2-6) of the effects of drought upon rangeland as shown by data collected within a hundred-mile radius of San Angelo, Tex., is applicable also to most of the western half of Texas and probably to other areas in the South- west drought area: Rainfall records for Sonora. Ozona, and San Angelo reveal subnormal precipitation 8 of the 11 years from 1943 through 1953. The average rainfall for this ll-year period was 15.6 inches at San Angelo, as compared with 24 inches for the pre- ceding ll-year period aDd a SO-year normal of almost 20 inches. Rainfall during the 8 dry years averaged almost 7 inches below normal. The accumulated deficit at San Angelo over the 1l~ ~real' period Is the equivalent of 60 inches of rainfall. The entire western half of Texas has been affected severely. Over much of the area, very little new grass was produced during the 3-year period [1951-53]. Clipping studies at the Ranch Experiment Station near Sonora show 20 pounds per acre of air-dry grass produced in 1951 and none in 1952 or 1953. During the latter part of this period, ranges have been relatively bare of lJalatable grass. Range feed has been mainly dry tobosa grnss, browse, bUrned pear and sotoI plus some annual weeds. Year-round feeding has been common on many ranches * . * Livestocl{ numbers reached a peak in 1943 just as the long period of dry years began and have decreased about 50 percent during the ll-year period. The only interruption in this trend tame following the one wet year (1949). An associated factor contributing to the upturn in numbers was the sharp rise in prices following 1049, due largel;y to the outbreak of war in Korea. Anticipating a continuation of the peak prices prevail- ing in the spring of 1951-, most ranchmen made strenuous efforts to maintain and, in some cases, to increase stoclting rates despite the rapidly decreasing range feed supply. Although ranges deteriorated during the drought, data in- (Heating the nature and extent of deteriorating of the range are SCRn'e und difficult to obtain. One crude measure of the effect of the drought on forage yields is the trend in livestock numbers and in the size of the feed bill. The extreme bareness of the rnnge during the winter and spring of 1954 suggests that adjustments in livestock numbers did not keep step with the decline in forage yields. Further evidence of this lack of ad- justment is the large amount of feed purchased from the fall of 1950 to the fall of 1953. An average of $25 was spent for feed per animal unit on 45 ranchoo which were well distributed over the area most affected by the drought, while the normal expenditure is approximately $3. The quality of the forage on the range, as indicated by plant composition, also deteriorated. Range management specialists base the classification on range conditions mainly on the extent to which climax species make up the plant population. Climax species are those species of plants that are most productive under a given set of soil and climatic conditions. Excellent range is made up of 75 to 100 percent of plants of the climax species. Good range contains 50--75 percent; fair range 25-50 percent and poor range 0-25 percent plants of the climax species. According to studies made on 8 of these 45 ranches by the Soil Conservation Service, the general condition of- the range was "fair" in 1950 and "poor" by 1954. At the Texas Range Station near Barnhart, where range management practices are being studied intensively, it was reported in Texas Agricultural Experiment Station Bulletin No. 786 that forage production was extremely low and plant density was seriously reduced during the low rainfall period 1951-53. The composition of the forage also was changed. High death losses occurred in an grasses except tobosa grass. At the same time, invader plants, such as mesquite trees and prickly pear, increased in number. These changes occurred in ungrazed exclosutes but not to the same extent as they did in heavily grazed pas-tures. California receives most of its precipitation during the winter, and its dependence on direct precipitation for cultivated crops is therefore less than in Texas, Nevertheless, soil moisture derived directly from pre- cipitation is an important part of the water resources in California, as a supplement to the surface and ground water applied to irrigated lands and as the only source of water for forests and rangelands, There are also ex- tensive areas of nonirrigated farming, chiefly of grai!1s, although the aggregate is small in comparison with the acreage of irrigated crops, Yearly yields from non- irrigated farming are related to yearly precipitation, but the relation is rather obscure because the timing of precipitation in relation to crop maturity is an im- portant element governing yield (p. B47). A more detailed statement concerning the effect of drought upon soil moisture would require data on the water-storage capability and the fluctuations in storage in the soil; these in turn would require data on the physical and chemical character of the soil, which may vary widely from place to place on a single farm. It may be presumed that fluctuations in soil moisture at any locality correlate to some degree with the qnantities made available by precipitation. But the intensity of precipitation is a factor that must not be overlooked. Rain may be so distributed throughout the year that all the water remains in the soil until it returns to the atmosphere; it may occur at such a rate as to result in some ground-water recharge; or it may occur in a few intense storms that cause overland runoff.