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<br />20 <br /> <br />U) <br />~ <br />:c <br />~ <br />z <br />.... <br />I <br />z <br />o <br />.... <br />~ <br />c <br />~ <br />.... <br />~ <br />.... <br />~ <br />~ <br />D: <br />~ <br /> <br />SEASONAL RAINFALL VARIABILITY <br /> <br />Seasonal rainfall in South Dakota can vary several inches <br />from year-to-year as shown below. Drought conditions are <br />characterized by persistance, from month-to-month, of high <br />temperatures ,and low rainfall. Looking at the dry years <br />natural pr~cipitation and precipitation expected with seeding, <br />it is immediately apparent that cloud seeding will not eliminate <br />droughts. In fact, the seeding effect is masked by the much <br />larger year-to-year precipitation variations. <br /> <br />, <br />! <br /> <br />I <br />I <br /> <br /> <br /> <br />4 <br /> <br />2 <br /> <br /> <br />40 <br /> <br />55 <br /> <br />70 <br /> <br />1974 <br /> <br />60 <br /> <br />65 <br /> <br />45 <br /> <br />50 <br /> <br />YEARS <br /> <br />Total May-August precipitation, averaged over South Dakota, <br />from 1930 to 1974~ is shown as a solid line. The dashed <br />line represents the precipitation expected with a 10% increase <br />through cloud seeding. The 45 year average natural precip- <br />itation is shown as a heavy solid line. As precipitation <br />was augmented through cloud seeding in 1972-1974, the solid <br />line during these years represents the precipitation which <br />would likely have been recorded in the absence of seeding. <br /> <br />24 <br />