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<br />r <br />I <br /> <br />i <br /> <br />rn"i' r, ., rJ <br /><..,I -' -,~ '"y' , d <br /> <br />GENERAL EFFECTS OF DROUGHT ON VVATER RESOURCES <br /> <br />TABh('J 4.-Adjustments for converting yearly logarithmic standard- <br />deviation ~mit8 computed on 7wsis of the period 1930-53 to those <br />computed on basis of the base period 1904-53 <br /> Station Adjustment <br /> in jogarith- <br />No I micstand- <br /> Name ard:devia- <br /> tion units <br /> Pacific border <br />1 Kill~S Hlver nt Piedra, Calif_________n__nn__________________ -0.072 <br />, Arroyo Seco near Soledad, CaUL_________________nnH_____n_ -,158 <br />3 Kuwoah River Drar Three Rivers, Callf-un_ _______un_n___ +.028 <br />4 Tlllc Hlvcrncar Portervillc, Callf____ ___n__nn__________n__ -.010 <br /> Central California, mean Ilsed for group_ _______u________ -.053 <br /> ~-- <br /> -~--- <br />8 Sunta Ynl1z RiVl'f above Gibraltar Dam near Santa Barbara, <br /> Calif______u___________________ ______u_ _______u_uu_____ -.297 <br />11 Arroyo Sl'CO near Pasadena, CaliL_ ________uu_____ ______u -.111 <br />14 San Hllbrid Hivl'r IWllr A7...sa, CllliLu__u_ ___u_u______ -.170 <br />2rl Sautl). Ann River Ilear Mentane, CaliLnu_ _____nn_n_______ -.299 <br />28 Santa YS!tbcl Cr{'ek lll'ar Mesa Grande, Calif ____nn_u_u___ -.263 <br /> Southern California, Ilwan used for group_ ___________ _____ -.228 <br /> Sonoran border <br />37 Vprde River below Bartlett Dam, Arlz________~___u_n____u__ -0.496 <br />40 Salt Hivpr at Roosevelt, AriL_______n________n__n_n_u____ -.297 <br /> ~- <br /> Mogollon Rim, mean used for groupn_nuu_ ______nu_ -_396 <br /> --~ <br /> ~~ <br />45 Oila RiV{'rnear Hed Hock, N, M{'x__nuu____~_ _n._n______ -.254 <br /> Uppcr Olla River, mean used for groupm ________n_u___ -.254 <br /> ~-~- <br /> ---- <br /> :\fiddlc Gila Hiver, mean used for group loon_n_ ____nn_ -.297 <br /> Great B/lBin-Colorado Plateau <br />29 <br />30 <br />31 <br />M <br />" <br />60 <br />02 <br />66 <br />71 <br />72 <br /> Great Plains <br />74 Colorado Rivcr at Ballinger, Texmnnnu__n____ ___nn_n_ -0.157 <br /> West-central Texas, mean used for groupnnu _u_ ------ -.137 <br /> ~~- <br /> -- <br /> South-central Texas, mean used for group2____uu________ -.157 <br /> -- <br /> --~- <br />80 Brazos River at Waco, Texu_u__unn_n____ _____nn_______ -.007 <br /> Central Texas, mean used for groupnu__ ______nnunn -.007 <br />1 No station in group with record for 1904-.53. Mean for Salt River near Roosevelt, <br />!\.riz., was used. 2 No statiollln group with record for 1904-.53. Mean for Colorado River at Ballinger, <br />ex., was used. <br />By expressing the year's runoff in terms of logarith- <br />mic standard-deviation units, the effects of differences <br />n size of drainage area, in yield per square mile and in <br />ercentage of average yearly runoff, are offset or greatly <br />reduced, These units also tend to offset the effects of the <br />variation between basins caused by differences in nat- <br />ral storage that result from different topography, ge- <br />logy, v,egetation, and effects of man's occupancy. Thus <br />ompa.rIson between two streams is possible in spite of <br />hese differences, because the logarithmic standard- <br /> <br />Beaver Riwr near Devver, Utab___________n________u________ <br />Sevier River at Klngstonij Utah________________n____a________ <br />Virgin River at Virgin, tnlL____u__uuu__u____n_n______ <br />Southwestern Utah, mean used for group__._ _uunu____ <br />Animas Hiverat Durango, Colo__________~___n_a_u___ <br />H.io Orunde near Del Norte, Colo__un____n_~nunnu____ <br />San Juan River at Rosa, N. Mex__nnnnun_"___nUnU_H_ <br />COllejas River near Mogote, Colo_"nn~_nun_u______nnuu <br />Hio Orandc at Otowi Bridge, near San IIldefonso, N. Mex______ <br /> <br />-0.340 <br />-.499 <br />-.441 <br />-.427 <br />.428 <br />-.453 <br />-.379 <br />-.324 <br />-.423 <br /> <br />Sall Juan Mountains, mean used for group___ <br /> <br />-.401 <br /> <br />(Jallinas River at Montezuma, N. Mex.____n__au__u____n__ <br />Pecos River near Pucrta de Luna, N. Mex_____nnnnnu____ <br /> <br />-.245 <br />-.156 <br /> <br />Upper Pecos, mean used for group___ <br /> <br />-.200 <br /> <br />T <br /> <br />p <br /> <br />u <br />o <br />c <br />t <br /> <br />B25 <br /> <br />deviation units reflect primarily the effect of the varia- <br />tion of precipitation on the year-to-year runoff from the <br />basins. Figure 5 illustrates runoff expressed in loga- <br />rithmic standard-deviation units in graphs for the six <br />stations whose records form the basis for figures 1 and <br />2. The same deductions drawn previously (p. B13) re- <br />garding severity and length of drought can be drawn <br />again, but in addition figure 5 shows the degree to which <br />year-to-year variations of flow in the six streams are in <br />unIson, <br />If there is sufficient unison of variation, Or homo- <br />geneity, among the record" from the 85 gaging stations <br />given in table 2, they can be the basis for evaluating the <br />drought for extensive areas in which the drainage basins <br />whose runoff was measured are representative. If ho- <br />mogeneity is lacking, the drought can be described only <br />by specific areas, and overall conclusions are unwar- <br />ranted. To determine whether there is unison of vari- <br />ation, or homogeneity, among the streams, statistical <br />correlative techniques were used. The yearly runoffs, <br />in logarithmic standard-deviation units, of pairs of <br />streams were correlated and the degree of homogeneity <br />was determined from the coeflicient of correlation-a <br />coefficient of unity indicating perfect homogeneity and <br />zero indicating no unison of variation whatsoever. A <br />correlation coefficient of 0.7 was adopted as the mini- <br />mum required to indicate homogeneity between two sta- <br />tions, The 24-year period 1930-53 was used, because it <br />is the longest period for which concurrent records are <br />available for all 85 stations used in the study. The min- <br />imum accepted coefficient of 0.7 is well above the sig- <br />nificance level of 0.41 for 24 independent events and <br />indicates that about half the variance between stations <br />has been accounted for. Because runoff is persistent <br />and not truly random, the number of independent run- <br />off events in 24 years is undoubtedly less than 24, but <br />even if the number is as low as 10 a correlation coeffi- <br />cient of 0,62 is still significant at the 5-percent level. <br />As a rule, the coefficients of correlation are highest <br />between nearby streams and decrease with increasing <br />distance. Among 22 stations in California, high coeffi- <br />cients of correlation indicate that the yearly deviations <br />of the streams from their medians are in remarkable <br />accord. The correlation of these streams with more dis- <br />tant ones resulted in lower coefficients; correlations with <br />streams in Arizona sometimes gave coefficients lower. <br />than would be expected by chance. Poor correlations <br />made it evident that not all streams in the ,Southwest <br />fluctuate in any semblance of unison, and the Southwest <br />cannot, therefore, be considered as a homogeneous unit. <br />However, by grouping those stations whose correla- <br />tions indicated a high degree of unison of variation, <br />regions were delineated such that the regional mean <br />