WMOD00071

• Applicant: Western Weather Consultants
• Project Name: Vail Pass
• Date: 11/1/1984
• Weather Modification - Doc Type: Application

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CHAPTER It

y
A DISCUSSION AND SYNTHESIS

INTRODUCTION

NeJ CallH' - . C. P. Patrick Reid, P_ J. Webb.er. and Donald A. Klein
,

This chapter Is intended to dra~ to~ether the main
conclusions of Chaot€r IV of this report vith
regard to the influence of cloud seedin~ on the
terrestrial ecosystems of the San Juan Mountains~
:Following a brief description of the field area. the
ecosystem components are considered separately and
then the possibility of linked interactions among
them. vhich may lead to either"damped or amplified
responses to snawpack augmentation. Is discussed. .
This treatment requires some speculation about poten~
tial impacts, especially long term oneS, since not all
of the predictions made hare are based upon statis-
tic:.aJ.ly' proven relationsh.1ps_ The 'speculation is.
. however. that. of scientlsts who have 'WOrked in the
'.-; San Juan Kounu.iD8 for 5 years and so is usefully
included in a general discussion of ecological
effects. bearing in mind the increased risk of error
whi..ch such speculation entails.

During: the 5 yeat: life of t.he -re.search. ~epo-rted
bere (1910-1975). the San Juan Mountains have
. ; been the site of a pilot project designed to test
the- .operational effectiveness of snowpack augmenta":,' .
tlon through a randomized seeding experiment.
Originally. it was anticipated that the project
vould ~ive e. 15 ~e'rcet\t inC'rease. in vinte-c snovpac.u;
that is ahout one half of the expected full poten-.
tial of vincer cloud seeding 10 the area. ~ubgequent
evaluation of t.he cloud deeding eX{Jed.l1lenc has led to
the conclusion that actual snowp8ck augmentation vas
below the anticipated 15 percent level (Howell. this
vol~ p. 5). Any aytlficially caused increase in the
saawpack of the San Juan Mountains has been imposed
on a region in which prec1p1tation and snow
accumulation is naturally n1ghly var1able: annual
snowfall there ranges between 35 percent less and
~~U ercent greater than the annual mean ot 4U cm
'Water equivalent V.e-. measured ove-r a year
period. ~ny of the estimates of ecologic impact
made in tbis study are based on the potential 30 per-
cent increase in me-an snovpack accumulation that vas
originally ass~ed to be possible in an operational
phase .o:f winter cloud seeding.

TIlE FIEUl AREA

In southwestern Colorado. tbe Continental Divide
makes a wide bend to the west around the headvaters
of the Rio Grande and through the San Juan Mountains.
The target area for cloud seeding has been a 3400 km2
area in the southern and eastern part of the range,
extending from the Colorado-New Mexico state line to
the Needle Mountains. Most of the field ..investiga-
tions of the San Juan Ecology Project have been
conducted in this target area (Figure 1. Chapter I).

In the target area. the Continental Divide runs almost
east-west and subsidiary ridges extend from it to the
south or southwest betveen tributaries of the San
Juan River. The topography of the area is generally
rugged with some of the peaks ~xceeding 4250 m ele-

vation. With the exception of Wolf Creek Pass, no
all-weather roads cross the mountain area and ~uch
of it lies within the Weminuche ~ilderness.

Geologically. this is a young pa'rt of the southern
Rockies and is. composed 1a'rgely of Tertiary volcanic.
tuffs and lavas, although metamorphic mater13ls of
Precamb'rian age are exposed extensively in the ~eedle
Mountains and G'renadier Range at the ~estern end of
thp. target area. Mesozo~c sedimentary materials are
found only at lover elevatlons.- This diversity of
paren~ materials, combined with the changes of
cl1ms~e and vegetation due to elevation and a his-
tory of multiple late-cenozoic glaciations, has-
pyoduced a complex pattern of 8011s and surficial
deposits; however. this complexity is typical of
th:e southern Rocky Moun~ains. , .ff'
Sec.,-r""n4: _,Q"... ed..,-
- cm~:Ct..iJsiONS . 'd" .

. ~ :;i;.",: :):~ .....--::. .-"

The results of-the San Juan Eco!o~Y Proiect sU~Rest
that there should be no. in::mediate. larlOl:e-scale
l~oacts on the terrestrial ecosyst~ of these .
mountains followi~ an addition of up to 30 percent
of the. normal snowpack, but wit no ad t on to
:- r.axitDUtlI. sno\lj)8cks.. ..Further. ouch of the vork re-
.;ported here SUl:!:l:!:ests that compensating Dec..~an1sms
'~itnin the studied ecosysteQS Rre such that any
i~?acts vould be buffer~d. at leas~ fur short periodS
~. of time. and of lesser.ma~nitude than the changes
,~, in snow conditions required to produce them.
~-:"i .' :'; _ ", '"__ ..' .
HoYever~ some parts of the mountain ecosystem ~re
much more susceptible to chanRes in 9noy conditions
~han others. so important local effects are ~ossible.
In general. these susceotible components n~e very
small parts of tbe entire system but their economic
or esthetic value may be much greater than their
mass or area SURRest. Remedial action is possible
in most. of these cases but has not been studied ln
this project., Our work has shown three eCOsystem
c onBnts to be most susceptible to inc'reased
snowfall: snowbank situations at elevations above
treeline; (2f elk herds (in other mountain ranges
~other big game spec1es may be simil~rly affected);
and 3) some-small mammal populat!ons~ especially
the deer mouse. Not all of these impacts are
. necessarll deleterious; an increase in the area of
snowbank edge habitats in alpine area may~ or examp e,
increase the niches available for rare plant species.

,.

ina!l even ln the small 8'reas where 'we predict
rea test impacts from inereased snow ate c anges
nvolved a're un i e y to approac t e magn u e 0
at e'r man-ma e mpacts on mounta n ecosystems. ow-
eve'r. it 6nou~d be rememberea tnat tney may act in
phase vith other man-made impacts and with natural
climatic changes. in which case the total effect
could be much greater than our studies suggest.

.~ . -,....- -~,._~'--

:-' .ll ~ Ste-l1'1ho-ff~:-Harold-Y-"':,and':Jack-D:-lVe6--{Ed~.)~1976-.- Ecp:l!>8-ic~l impacts of snO\lPack augr..en~<!.tit,l', i.n l'\~
. San Juan Kountains.-- Colorv.do: Final Report, San Juan Ecology Project, Colorado State Univer:!dty l'u::l.;
Fort Collins.
!I Present Address: INSiAAR. University of Colorado. Boulder. Colorado 80309.

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