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Last modified
7/28/2009 2:27:13 PM
Creation date
10/1/2006 2:10:45 PM
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Template:
Weather Modification
Applicant
Western Weather Consultants
Project Name
San Juan
Date
11/1/1984
Weather Modification - Doc Type
Application
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<br />-Lower Soil Te~erature <br /> <br />A noticeable decline in forest populations of small <br />mammals occurred fOllowinp; winters of heavy snowfall. <br />This was most evident in the numbers of deer mice <br />(Peromyscus maniculatus) but it was also found in <br />chipmunks (Eutamlas mlnimus) and in Microtus spp. <br />The basic reason for the population decline derives <br />from the delayed 2rowth of p-ssp.nrial sDring fnon~ ~nn <br />results primarily from a delay In breedin2 so that <br />.;ewer litters are produced. The delayed growth of <br />plants was a function of lower soil temperatures and <br />the lon~er snow cover. No similar effect was found <br />on the toad (Bufo boreas), or pocket gopher (Thomomys <br />talpoides) populations. <br /> <br />-Deeper Snowpack <br /> <br />As snow depth increased. elk (Cervus candensis) ~ <br />to areas where snow was shallower than 40 em. They <br />avoided re ions with more than 10 em at penetrasr,e- <br />snow depth. A 15 percent increase n snowpac may <br />decrease available elk winter range by H percent. <br />SprinR movement of elk was more stron~ly associated <br />with the.start of new Rrowth in mountain meadows than <br />directly with the recedinK snowline. Ample habitat <br />was available for elk calving below the snowline and <br />without reRard to snow deoth. <br /> <br />~lcrobes <br /> <br />Plant litter in the tundr8 decreased in areas of <br />deeper snowpack. This nresumablv reflects removal by <br />the additional flux of water through tbe system rather <br />than an increase in decomposition rates. <br /> <br />Abiotic Factors <br /> <br />The effects of the snowpack on soil erosion resulted <br />from the greater area of bare soil left by the decrease <br />1n vegetative cover around snowbanks. Those predicted <br />for the tundra area of the San Juan MOuntains derive <br />from either the additional snow depth or the additional <br />meltwater produced by cloud seeding. <br /> <br />-Deep~r Sno~~ck <br /> <br />If the area of lon2-lastinR snowbanks expand after an <br />increase in snowfall. local chanKes in the rates of <br />soil erosion on the bare surface around them may in- <br />crease by a factor of 10. This effect should not <br />extend beyond the immediate vicinity of already ex- <br />isting snow dritts and 80 should not be important re- <br />donallv. <br /> <br />-Additional Meltwater <br /> <br />Theoretical considerations SUP;Kest that an increased <br />streamflow generated by cloud seediag should be <br />assoc1ated with an increase in the total amount of <br />dissolved material removed from the target area. This <br />is supported by empirical observations of rock weather- <br />ing rates and stream 'Water quality in th.:! tundra <br />environment. However. this effect will h~ ~lighr ~nd <br />should not be concentrated spatially. <br /> <br />-HistorIcal Climato10&y <br /> <br />Temperature fluctuations over the last 120 years in- <br />dicate a cooling trend from the late 1960'~ to about <br />1930 when a reversal occurred; precipitatiun trends <br />are inversely relati!d to temperature tr"i:nds. TheS.~ <br />trends .Ire quit:: diff~r<!nt fror:! t:-l('s~nvted in :\:1'-0:: <br />parts of the :\'orther"11 HE"'lisphe".~. -:;''''.''0'1;1.!. ;).....~ 't.,. <br /> <br />tion fluctuations show rapid transitions from relative- <br />ly dry to relatively wet modes. <br /> <br />-Silver <br /> <br />No significant increase in stIver concentration were <br />found in the target area. except in small areas near <br />generator sites. after four winters of seeding. ~ <br />deleterious effects of silver iodide additions have <br />been noted at concentrations which could be egpected <br />due to cloud seeding. <br /> <br />HISTORY AND DESIGN <br /> <br />The San Juan Ecology Project was established as one of <br />a complex of investigations arising from the need to <br />explore the possibilities of increasing the availabil- <br />its of water in the United States Southwest. In 1968 <br />Congress authorized the Bureau of Reclamation to <br />initiate weather modification pilot projects to test <br />the feasibility of large scale winter cloud seeding <br />which showed promise of being an economical technique <br />for augmenting the flow of the Colorado River (Division <br />of Atmospheric Water Resources Management 1970). <br />Analvsis of previous research findin~s indicated that <br />th~ most likely chance of success would come from <br />winter seeding of orographic storms over some of the <br />high mountain areas situated in the Upper Co~orado <br />River Basin. Grant et al. (1968) tested this approach <br />on a limited scale at Climax, Colorado, and found <br />significant increases in snowfall when seedin~ exper- <br />timents were performed under specific weather situations. <br />'Knowled e accruin from this study~ and from two others <br />in Colorado Steamboat Springs and Wolf Cree Pass. <br />and from a National Academy of Sciences Report (1964), <br />led to the conclusion that care tully managed Wlnter <br />cloud-seedin~ techniques could prOduce a 10 to JU <br />percent increase in mountain snowfall. The Bureau of <br />Reclamation designed the Colorado River Basin Pilot <br />Project (part of Project Skywater) to test this <br />possibility on a sub-operational scale. The most re- <br />cent statement on the effectiveness of this design is <br />given in summary form by Howell (this .Chapter). <br /> <br />The San Juan Mountains of southwestern Colorado were <br />chosen as the site of the cloud seeding pilot project <br />because of their strategic location for intercepting <br />winter orographic storms deriving from the southwest <br />which would also ensure relatively frequent occurrence <br />of a cloud-top temperature condition calculated to be <br />within the mast effective seeding range of above -26C. <br />The original area destined ~o receive ~he cloud-seed- <br />iog experiment was 8.550 km (3,300 mi ) on the west- <br />ern side of the Continental Divide. and above 2,900 m <br />(9,500 ft) elevation (Fig. 1)., <br /> <br /> <br />."~ <br />.::; 1.i"11 <br /> <br />. :.. .. <br /> <br />U~I.l "TU <br /> <br />'_ll......C... <br />1-",,,..... c." <br /> <br />~OIIU' IOTU <br /> <br />1-..........,..... <br /> <br />~ <br /> <br />J <br /> <br />r.-;:~ur,. 1. Sa;., Juan cl....ud :ieeding target area, and <br />tn::t>usiv2 .3 [l.:d_,' sit-=s. <br /> <br />-27- <br /> <br />A-13-3 <br />
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