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<br />MARCH 1973 <br /> <br />140 <br /> <br />Q; 120 <br />.. <br />"- <br />.. <br /><.> <br />.. 100 <br />'0 <br />~ <br />'0 <br />e <br />c <br />~ 80 <br />" <br />~ <br />.... <br />e <br />. 60 <br />0 <br />;;: <br />g <br />;: 40 <br />c <br />.. <br />Ul <br />.. <br />"" <br />:; <br />.... <br /> <br />H. J. MOREL-SEYTOUX AND F SAHELI <br /> <br />330 <br /> <br />. Seeded Season <br />. Unseeded Season <br /> <br /> <br />I." <br />. <br /> <br />19)"0 19:7 <br />1967 <br />19'6~ 195j, ,,961 1943 <br />,.,~ . <br />1964. <br />1946 <br /> <br />I." <br />. <br /> <br /> <br />Target: Alomosa Creek above Terrace Reservoir, C.olorado <br />ContrOl: Piedra River neor Piedro, Colorado <br />Regression Line Based on 27 Years of Record <br />Significance Level:96% (one-tailed test) <br />Apparent Relallve Increase: 17 % <br />Apparent Mean Seasonal Increase: 11,000 ocre- ft. <br /> <br />-1955 <br /> <br />. <br />1963 <br /> <br />00 <br /> <br />120 160 200 240 280 320 360 400 <br />Control Seasonal (April-August) Flow In Thousands of Acre - Feet <br /> <br />440 <br /> <br />480 <br /> <br />40 <br /> <br />80 <br /> <br />FIG. 8. Regression line between target seasonal runoff and control seasonal runoff. <br /> <br />a. Estimation of the mean runoff changes <br /> <br />Though various aspects of research on cloud modifica- <br />tion have been conducted successfully, it is still difficult <br />to determine accurately its quantitative effect. Indeed, <br />one of the purposes of the Colorado River Basin Pilot <br />Project is to determine the exact magnitude of the <br /> <br />increase in precipitation on a large areal scale. Following <br />this experiment, it may be possible to isolate the majQr <br />factors that determine the magnitude of the increase <br />of precipitation. At present it is a somewhat accepted <br />opinion that the mean increase of precipitation by <br />cloud seeding is proportional to the natural mean <br /> <br />900 <br /> <br /> 800 <br />Q; <br />., 700 <br />La.. <br />, <br />~ <br />v <br />.. <br />'0 600 <br />~ <br />.., <br />e <br />:i: <br />" 500 <br />0 <br />.c <br />I- <br />,!; <br />;0 400 <br />0 <br />;:;: <br />g <br />0 <br />on 300 <br />0 <br />., <br />Ul <br />Q; <br />'" <br />~ 200 <br /> 100 <br /> <br />-' <br /> <br />'1..: I <br /> <br />. <br /> <br /> <br />· Seeded Season <br />. Unseeded Season <br /> <br />'965 <br />. <br /> <br />. <br /> <br />1961 <br />. <br /> <br />. <br /> <br />Combined Ison Juan River at Pagosa Springs, Colorado <br />Targets South Fork Rio Grande at South Fort<, Colorado <br />Alamosa Creek above Terrace Reservoir, Colorado <br /> <br />Combined ILake Fork at Gateview, Colorodo <br />Controls Animas River ot Howardsvllle, Colorado <br />Piedra River near Piedra, Colorado <br /> <br />Regression Line Based on 26 Years of Record <br />Significance Level: 99 % (one - tOiled test) <br />Apparent Relative Increase: 20 % <br />Apporent Mean Seasonal Increase: 78,000 acre-feet <br /> <br />o <br />o 100 200 300 400 500 600 700 800 <br />Control Seasonal (April-August) Flow in Thousands of Acre-Feet <br /> <br />FIG. 9, Regression line between total target seasonal runoff and total control seasonal runoff. <br />