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Appendix to Question No. 11 F"r"..... 'tf'c Pro>fl4cc L...~,..I..J h, Lf "1/,<:. I""'f".....h l:[ 51"',..... E......t....,...,<::......._-.-f.. Lt!-o.. L...J, wr!..s bc~ 1::.1"::...' I Lf7~ The computations of increases due to se~dinb were cx~mlned to see if the augmented amount tended to be relatively large when the natural snowfall was large, o~ conversely. This set ot datu is shown in Figure 14(a). Although limited in size, the sample indicates that there is a positive relationship. The natural snowfall and amounts produced by B~eding have a linear correlation of 0.6. The increases were also co~uted as s percentage of the natural snowfall. Fi.gure 14(b) shows that this per- centSl;e is not dependent on natural snowfall.: Thf:!refore. the sadie percent- BEe snow augmentation may be used in both low and hi~h years of natural snowfall. We ~y sUmmarl~e the dls~usslon of snowlall augmentation as follo""'s: (1) The most probabLe increase in snowfall at elevations above 8000 ft that can be re31i%cd by s~cding 15 in the range from approximately 20 to 25 p~rcent, as _ an average figure fOT the basin over a period of at least several years. In our judgment the chance that subsequent, iong-term data will show that this figure is less than 10 percent or great~r than 35 percent is less than one in ten. This assumes that state of the art cloud seeding is done in an optilllal lIlanner. If it is not done optimally th~n the percent increase in snowfall will be less. (2) The increases are produced mninly by changing hours in which little snowfall ~ould have occurred naturally into hours of significant snowfall. As a result, the days with relatively large amounts of snow (e.r.. amounts greater than one half inch of water equiv31ent) w111 be one and n h~lf to twice as frequent (see figure II). (3) .Thc proportional incre~se in snowfall produced by seed.1n~ will be the same whether the season ls lI'et or dry. (4) The kernel of the effect of seeding is that it will make the snowfall amounts of the target area similar to the natural snowfall that exists at elevations 500 to 1000 ft higher in the mountains. As a simple but reasonably accurate rule for computing ~u_~~nted seasonal snowfall, one may apply percent~gc increases to the sea.:.o~al Snowfall averages. However, the percentage incrc3scs that should be applled to thc differcnt localltles are not well known at this time. In the light of diSCUSSions wlth Professor Grant and our cOlllputa- Uons given c3rlier, lI'e selected the percentage Increases shown In Fll;ure 15 3S the PlOSt probable estimates. These percentage Increases were then applied to the seasonal snowfall of Figure 7 to obtain the average snowfall (water equi.valent) that would be produced by seeding methods that C:ln be implemented within the next five years (Figure 16'- This map, and the h..o that follow, were used extenSively in the study to ('stim~tc hydruloglC COlHlitions and the effects on ecological, social, ~nd {'CUIlOmlC sy.:ncms; there/ore. tlley arc C1Itremel}' important.