WMOD00271

• Sponsor Name: North American Interstate Weather Modification Council
• Project Name: Fiscal Year 2008 Request
• Title: Fiscal Year 2008 Request
• Prepared For: NAIWMC
• Prepared By: JM McClintock Consulting, Inc
• Date: 2/24/2007
• Bill Number: HR2995 & S.517
• Weather Modification - Doc Type: General Information

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North Aml'f'kan Inh.'r.'\hllt.' \\'('0111)('1' l\]ndifkatiuII Coundl
ww......nuiv,nll.:.tlrg

"Facilitating the exchange of Interstate/Interprovincial atmospheric
resource management information."

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Answcrs to Frc1lucntly Askcd Qucstions about
Cloud Sccdin/.: to AU/.:Illcnt Mountain Snowpacks*

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Q. DOlOS doud "t.'t."(linJ: for .o.nowpuck aUJ.:mt.'nlallnn feall)' "ork?
A. Yes! The W('illhl'r I\1oditkaliun A~so....iati()n. World Melt"Orological Organization (WMO). American
Meteorological Society (A:\1S) and the National Academy of Sciences (NAS) all slale thallhere is strong evidl'ncc
for seasonal prl'Cipilalion incrca..cs o\'l:r nalUral prt.'Cipilation. The A1\15 further ...talcs thai increases of about
1O~ aa' fca.-.iblc. To achieve !o.uch increases, wcll~dcsig.m-d and conducted projl'Cts muM ht' open/fl'tJ Oil II /(11/1<.
reml Of/d cmllilluing hll.li.\", /lot jll.\'l during drol/ghts. Such projl.'Ch will help fill reservoirs for use during times of
greater need, such a\ drou!jhts. Expcrimenh in Colorado, Montana and Australia ..howoo stati"tically "ignificant
incrcllsC's of 101K or greater .2.3.

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Q. Whllt an' tltl' l'mlronnwntal and hl'aUh dTl'cls or sel'din/.: mllll'r1al and Its dfl"l.'1 on clouds and
prt.'t'lpitation?
A. Minimal. The most common sel-ding material. !>>ilver iodide, is U\l.-d in very minute amounts. The typical
concentration of silver in rainwater or !>>now from a !>>el.-'dt-d cloud is less than D.I microgmm per liter (one part in
]0.(0),000,000). This is well heiow the acceptilb]e concentration of 50 micrograms per liter, Sl't by the U. s.
Public Ilcalth Sl'rvice. r..lany region!>> have much higher concentriltions of !>>i]Vl'r in the soil lhan are found in
prt'l'ipilation from ..et-'dl-'d clouds. Thl' concentration of iodine in iodill''{1 salt u..ed on food i.. far above the
concenlnllion found in prtocipitation from a set>dt>d storm. National Environmental I'olky Act compliance for all
cloud sel.-'ding environmental impacb has Ot.'Cn demonstratl.-'d by pa\t studie\. The Uureau of Rl.'Ctamation
(Rl.'Clilmation) extensively studied l.'nvironmental and health impactsOJ'. The toxicity of silver and silwr
compounds (from silver iodide) was shown to bc of tow order. According to Rl.'(:lamation. the tiny amounh of
silver uSt'd in cloud !\Cl.,(\ing are ]00 time!>> Icss than industry emissions into the atmosphere in many pam of the
country, or individual exposure from tooth fillings. Accumu]ations in the soil. vegetation, and surface runoff have
not bcl'n large l'nou~h to measure above natural background7. A 1995 en\'ironml'ntal assesslTk.'nl in the Sierra
Nevada of California and a 2004 !'>lUdy in Au\tratia conl1rmt-'d these earlier findings.

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Q, Whllt art.. lhl" impal'l<\ of additional !Ono,","!
A. An environmental assellsment report in California~ investigated the impach of an assumed weather
modification-induced prt'Cipitation increase of 5 - 7.51K on weather dementll. hydrologic and phy!'>iographic
phenonll'lla. plant and anima] communitie!'>, (he hum.iIl environment, and land and water rl'Sourcc usc. The rl'port
concludl.-d that there would he no significant impact on thl'se environmental sectors. The percentage increasl's
from wcathl'r modification are much smalll'r than inter-annual variability of natural prl.'l'ipitalion. which can be
severa] hundred percl'nt~. Research conducll.-'d in the Uinta ~lountains of Utah indicall.-'d that "An increa!>>e of I DI1
in the a\'eragl' snowpOlck is clltim;l1l.'(\ to prolong thl' 75% snow-free date by 0.7-].5 days"lO. An exhau!'>live l1\'e-
yl'ar el'ologicalllludyll in Ihl' SOln Juan Mountain!'> of Colorado condudl.-'d that .....thl're should he no imml'diate.
large-scale impacts on the tt'rre!'>tria] t'Cosystems of these mountains following an addition of up to 30 pcrcent of
the normal snowpack..:' Furthermort', all opl'raling projl.'Cls in lhe We!'>tem U.S. have SU\I)Cnllion crileri;t
designed to slOp cloud sCl.'ding anytime there i\ a flood threat. Additionally. watl'r manageml'l1I personnel from

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