WMOD00258

• Applicant: Western Weather Consultants
• Project Name: Vail & Beaver Creek
• Date: 11/1/1987
• Weather Modification - Doc Type: Application

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-Lower Soil reo~erature

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A noticeable decline In forest populations of small
mammals occurred followinll. ....inters of heavy 5nololfall.
This was most evident In the numbers of deer mice
(Peromvscus maniculatus) but it was also found in
chipmunks (Eutamias minimus) and in Microtus spp.
The basic reason for the pODulatjon decline derives
from the delayed 2rowth of p~~p.nri~l ~nrinv fnn~~ ~nn
results primarily from a delay In breedine so that
~fewer litters are produced. The delayed gro....th of
plants ....as a function of lower 5011 temperatures and
the lonll.er snow cover. No similar effect ....as found
on the toad (Buro boreas). or pocket gopher (Thomomys
talpoldes) populations.

-Deeper Sno~ack

As sno.... dePth increased, elk (Cervus candensis) ~
to areas where snow was shallower than 40 cm. They
avoided regions with more than 10 cm ot penetrasre-
snow depth. A 15 percent increase 1n snowpacK may
decrease available elk winter range by 8 percent.
Sprin~ movement of elk was more strongly associated
with the start of new ~rowth in mountain meadows than
directly with .the recedinR snowline. Ample habitat
was available for elk calving below the snowline and
without reRard to snow depth.

l"Iicrobes

Plant litter in the tundra decreased in areas of
deeper snowpack. This presumably reflects removal by
,the additional flux of water through the system rather
than an increase in decomposition rates.

Abiotic Factors

The effects of the snowpack on soil erosion resulted
from the greater area of bare soil left by the decrease
,in vegetative cover around snowbanks. Those predicted
tor 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 Sno~flck

If the area of 10n2-1a5tin2 snowbanks e~pand after an
increase in snowfall. local chanRes in the rates of
soil erosion on the bare surface around them may in-
c~ease by a factor of 10. This effect should not
extend beyond the immediate vicinity of already ex-
isting snow drifts and so should not be important re-
donallv.

-Additional Meltwater

Theoretical considerations su est that an increased
streamflow generated by cloud see fng should be
associated with an increase in the total amount of
dissolved l:l3terial removed fro::l the target area. This
is supported by empirical observations of rock ~eather-
ing rates and stream ....ater quality in th~ tundra
envlronrne~t. However. this effect ~ill ~e 31i~hr ~nd
should not be concentrated spatially.

-Historical Clirr.~tolo&y

'!'el:lperature fluctuations o....'cr tho:!: last 1~0 y~ars in-
dicate a cooli~g trend from the late 1860's to 3bout
1930 \.:hen a reversal occu.rred; pr(!cipic:tcion crends
are inversely n~late:l to te::l;c>cr:1ture t.,:rods. Thes."
trends are quit~ dif~0r~nt from t.ir~C:'Jted irl
parts ~..,f the S,jrt":1o::rn !-!e;:'lisphe~~. .;;'.~ 'L,:l:c1; ;~' _L.'~.'-

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

-Silver

~o significant increase in silver concentration were
found in the target area, except in small areas near
generator sites, after four winters of seedin~. No
deleterious effects of silver iodide additions have
been noted 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 ....ater 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 ....inter cloud seeding
....hich sho....ed promise of being an economical technique
for augmenting the flow of the Colorado River (Division
of Atmospheric Water Resources Management 1970).
Analysis of previous research findin~s indicated that
:the most likely chance of success would come from
winter seeding of orographic storms over some of the
high mountain areas situated in the Upper Colorado
River Basin. Grant et .'11. (1968) tested this approach
on a limited scale at Climax, Colorado. and found
siKnificant increases in snowfall when seed inK exper-
liments were performed under specific weather situations.
'Knowled e accruing from this study. and from t~ others
in Colorado Steamboat Springs and Wolf Creek Pass .
and from a National Academy of Sciences Report (1964),
led to the conclusion that care tully managed w~nter
cloud-seeding techniques could produce a 10 to JU
percent increase in mountain snowfall. The Bureau of
Reclamation designed the Colorado River Basin Pilot
Project (part of Project Skywater) to test this
possibility on a sub-operational scale. The most re-
cent Statement on the effectiveness of this design is
given in summary form by Ho....ell (this ~hapter).

The San Juan Mountains of southwestern Colorado ....ere
chosen as the site of the cloud seeding pilot project
because of their strategic location for intercepting
winter orographic storms deriving from the southwest
which would also ensure relatively frequent occurrence
of a cloud-top te~perature condition calculated to be
within the most effective seeding range of above -26 C.
The original area destined 20 receive 2he cloud-seed-
ing experiment was 8.550 km (3,300 mi ) on the west-
ern side of the Continental Divide. and above 2.900 m
(9.500 ft) elevation (Fig. 1)..

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