WMOD00246

• Contract/Permit #: #95-1
• Applicant: Western Weather Consultants
• Project Name: Vail/Beaver Creek
• Date: 11/1/1995
• Weather Modification - Doc Type: Application

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-Lower Soil Te~erature

A noticeable deeline in forest 'populations of sm3ll
mammals occurred . followin~ \linters of heavy snowfall.
This \las most evident'in the numbers of deer mice
(peromvscus -maniculatus) but it was also fou~d in
chipmunks (Eutamias minimus) and in Microtus spp.
The basic reason for the population decline derives
from the delaved 2rovth of p.98p.nrial goring fnnrlR ~nrl
results primarily from a delay in breedin2 so that
.fewer litters are produced. The delayed growth of
plants was a function of lower soil temperatures and
the 10n~er snow cover. No similar effect was found
On the toad (Bufo ke.!.!.!!), or packet gopher (Thomomvs
talpoides) populations.

-Deeper Snowpack

As snow depth increased. elk (Cervus candensis) ~
to areas where snov vas shallower than 40 cm. . They
avoided re ions with ~re than 70 em at penetra~
snov depth. A lS percent ncrease n snowpac may
'decrease available elk winter range by H percent.
Sp~inK ~~ement of elk was more stronRlv associated
with the-start of new Rrowth in. mountain meadows than
directly with .the recedinR snowline. Ample habitat
was available for elk calvin~ below the snowline and
without re2ard to snow deDth.

'Microbes

Plant litter in the tundrA decre..ad in areas of
deeper anowpack. This nremumablv reflects removal by
the additional flux of water through the system rather
than an increase in decomposition rates.

Abiotic Factors

The effects of the 8no~ack on soil erosion resulted
from the greater'area 0 bare soil left b the decrease
. n vegetat ve cover around sno an a. Tho.. predicted
for the tundra area of the San Juan Mountains derive
from-either the'additional snow depth or the additional
meltwater produced by cloud seeding.

-Deep!!r Sao1l,P.8ck,
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1/ the areA of'''lonJl:''lastlnJl sno",banks expand after an
increase io-:anovfall. local chanRes in the rates of
. soil er08ion; OQ' .'the bare surface around them may in-
crease by a factor of 10. This effect should not'
'extend-beyond the~immed1ate vicin1t of alread ex-
SC og snow r t.'an so 8 au d not be important re-
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.-.\dditlonal Keltwater ~
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Theoretical considerations su est that an increased
streamflow senetated by cloud see ing should be
associated with an increase in the total amount of
dissolved material removed from the target ar~a. This
is supported by empirical observations of rock weather-
ing rates and stream. water,'quality in the tundra
environment. However. chis effect ~ltl he ~lt~ht and
should not be concentrated spatially.

~istoricaL Climatolo&v

.temperaturil fluctuations over the last 120 yti!ars in-
dicate a cooling trend from the late 1860's to 3bout
1930 vhen a reversal occurred; precipitatiun trends
are inverselY relate:! to temi>eroture tr.;uds. T"~g~
trends arc qult.3 differo.!nt f:-or:! t:I(~~<!Il'Jt<,~d In ;.,1:1:..
parts vi the ~orthern He.:'lij'lph~r.:. ;".1 ',.loa 1 p"'. ': t,~ 1 :,.\"

tion fluctuations show rapid transitions from relative-
ly dry to relatively wet modes.

-Silver

No significant increase in silver concentration were
found in the target area. except in small areas near
generator sites. after four winters of seed in . No
eterious effects of silver iodide additions have
bee ted at concentrations. which could be expected
due to cloud seeding.

HISTORY AND DESIGN

The San Juan Ecology Project was established as one of
a complex of investigations arising from the need to
explore the possibilities of increasing the availabil-
its of water in the United States Southwest. In 1968
Congress authorized the Bureau of Reclamation to
.initiate weather modification pilot projects to test
the feasibility of large scale winter cloud seeding
which showed promise 9f being an economical technique
for-augmenting the flov of the Colorado River (Division
of Atmospheric ~ater Resources Management 1910).
Analysis of previous research findin~s indicated,that
:the most likely chance of success would come from
winter seeding of orofraphic storms over some of the
high mountsin areas s cuated in the Upper Colorado
River'Basin. Grant et al. (1968) tested this approach
on a limited scale at Climax, Colorado, and found
significant increases in snowfall when seeding exper-
'imenta were performed under specific weather situations.
'Knowled e accruln from this study, and from tWO others
in Colorado Steamboat Springs and Wol Cree Pass,
and from a National Acsdemy of Sciences Report (1964).
led to the conclusion that caretully managea wlnter
cloud-seeding techniques could produce a 10 to JO
percent increase in mountain snowfall. The 8ureau of
Reclamation designed the Golorado River Basin Pilot
Project (part of Project Skrwater) to test this
possibility on a sub-operational scale. The most re-
cent Btatement on the effectiveness of this design is
given in Bummary form by Ho~ell (this ~hapter).

Tbe San Juan Hountains of southweatern Colorado were
chosen as the aite of the cloud seeding pilot project
because of their strategic location for intercepting
winter orographic storms deriving from the southweat
which would slso ensure relatively frequent occurrence
of a cloud-top teQperature condition calculated to be
within the most effective seeding r~Dge of above -26C.
The original area destined ~o receive ~he cloud-seed-
ing experiment was 8,550 km (3,300 m1 ) on the west-
ern side of the Continental Divide, and above 2.900.
(9.500 ft) elevati~n (Fig. 1)..

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