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<br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />II <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />t <br />t <br />t <br />t <br />t <br />. <br />t <br />t <br />. <br />. <br />. <br />. <br />t <br />t <br />t <br />t <br />t <br />t <br />. <br /> <br />Chapter <br />2 <br /> <br />Precipitation enhancement technology <br />A scientific technology for obtaining additional water <br /> <br />The current status of precipitation enhancement technology <br /> <br />The current status of precipitation <br />enhancement technology has been addressed <br />by four of the major organizations that have <br />dealt with weather modification during the past <br />50 years: American Society for Civil Engineers <br />(ASCE), Weather Modification Association <br />(WMA). American Meteorological Society <br />(AMS), and Wor1d Meteorological Organization <br />(WMO). The position of these organizations on <br />weather modification. with specific references <br />to convective glaciogenic and hygroscopic <br />seeding. are summarized below. <br /> <br />American Society of Civil Engineer.; <br /> <br />The ASCE Policy statement #275 was <br />approved by the ASCE in May 2003 (ASCE <br />2003). The policy stales: <br /> <br />The American Socie~ of CMI Eng;nee<s (ASCE)_ <br />and encourages the protection and ~ de~f <br />r:J the Nation's atmospheric water {also known as <br />'Neare modification. '" .d<Jud seedngl for benelidal <br />uses. Sustained suppa! fer alJ"Tlostileric water data <br />CXJIIecI:ioo, research. and operatia'lal progr<rn5. and !l1e <br />careU evaluations of such efforts indudiog the <br />assessment of extra-area and Iong-telm enviraYnental <br />effects. is essential for prWenl develqmenl <br /> <br />Weather Modification Association <br /> <br />The WMA's position on summer precipitation <br />augmentation is provided below \'NMA 1986). <br /> <br />The capaljlity to augment summertime IXOOpitation in an <br />area-'Nide fashioo is prorrising. Assessments from some <br />operational and some research projects are encouraging <br />especially when a seeding mode is ~yed whidl <br />allows seIedive seeding of indMdual cbuds. <br /> <br />Evaluations of operationally oonducted summer <br />IXOOpitation atqnet1tation J)'Ojects present a diffioJ~ <br />problem due to ll1eir not'l-i'andoo'ized naltire and !l1e <br />normally high varialjlity (Iempctal and spatial) present in <br />summer time rainfall. Recognizing these evaluation <br />limitations, !l1e results of many of these evaluations have <br />indicated a positive area-wide seeding effect in <br />precipitation. <br /> <br />American Meteorological Society <br /> <br />The AMS's position on precipitation increase <br />by glaciogenic and hygroscipic seeding <br />techniques of convective douds is provided <br />below (AMS 1998). <br /> <br />Heavy gladogenic seeding of sorne warm-based <br />convective doods (bases at ., OCC or wanner) can <br />stimulate ufXitatls thrcugh added latent heat release (a <br />dynarric effeel) and consequently ro.ase ~pitation. <br />I-k:JoNever. convincing evideoce that such seeding can <br />increase rainfall rNef E!ClJI'101lcaIIy significant areas is not <br />yet available. Seeding to enhana:! coalescence or affect <br />other warm rain ;:rocesses within clouds having surrrrWt <br />temperatures ~ than alx\rt ere has projuced <br />statislically aa::eptable evidence of accelerated <br />~tion formation 'Mthin drJLKjs. but evidence of <br />rainfal ~ at!l1e ground has not been obtained. <br /> <br />14 <br />