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<br />properties of segmemed snow profiles show considerable promise (I.\' possible means of <br />qu(mtijj:ing precipitation ulIJ{mentation OWl' basin-sized target areas. <br /> <br />American l\leteoroloeical Socicl\' (1998) <br /> <br />"Precipitation Increase <br /> <br />There is statistical e\'idence that precipitation }rom supercooled oroJ{raphic c!ollcl\' <br />(clouds that dewlofJ over mountains) has been seasonal(r increased by about 10%. The phy.~ical <br />cause-and-effect relationships. however, have not beenful(v documented Ne\'ertheless, the <br />potentialfor sllch increases is supported byfield measurements tlnd nllmerical model <br />simulations .. <br /> <br />World I\leteoroloeical On!anizlltion (200.J) <br /> <br />"Precipitation (Rain and Snow) Enhancement <br /> <br />This section deals with those precipitation enhancement tedlt/i'll/es that haw a scientific <br />basis and that ha\'e been the subjects of research. Other non-scientific and unprol'entechniques <br />that (Ire presellfed from time to time .\'hould be treated with the required suspicion and calltion. <br /> <br />Orographic mixed-plw.w: cloud ,\y-\.tems <br /> <br />In our present .Hate of knowled[{e. it is considered that the glaciogenic weding ofclom/s <br />fi)rmed by air flowing on'r mountains 0.0;"1'5 the best prospects for increasing precipitation in an <br />economical(J'-viable manner. 111ese types ofcloll(b. attracted great intere,\.( ill their modification <br />because of their potential in terms of water management, i_e. the possibility ofsloring water in <br />resen'oirs or in the snawpack at higher c:lemlions. l1/ae is statistical e\'idence Ihat, under <br />(.'erlain conditions, precipilalion from supercooled orographic clouds can be increased with <br />exi.5ting lee/lIli'll/es. Stalistical ana(vses of surface precipitation records from some long-IeI'm <br />projects indicate Ihat seasonal increases haw been realbed. <br /> <br />Physical studies ".\.ing new ohservational lools and supported hy numerical modeling <br />indicate that supercooled liquid Inlier exists in amounts suJ)icient to produce Ihe ohsen'ed <br />precipitation increases and could be tapped ifprol'cr seeding lee/mologies u.ere applied The <br />processes culminating in incn'used precipitation hm'e also been direclly obserwd during <br />seeding experiments conducted (H'er limiled spatial and temporal domains. While .weh <br />obsl!n'alions further .mpporlthe re.wlts of statistical af1(l(~'ses. they haw, 10 date, been of limited <br />scope. The cmlse and effect relationships hm'e nOl bl!enfull)' documented. and ,hus the <br />economic impact qfthe increases cannot be assessed. <br /> <br />This does not imply that thl! problem of precipitation enham'('menl in slIch Sil/wliom. is <br />so/l'ed. .\llIch work remains 10 be done 10 strengthen the result.\. and produce slronger statistical <br />and physical evidence that the increases occurred o\'er the target area ami m'er a prolonged <br />period of lime. us well as to search for the existence of any extra.area efft!CI.\'. Existing method~ <br />