WMOD00593

• Contract/Permit #: 14-06-D-7052
• Title: Ecological Impacts of Snowpack Augmentation in the San Juan Mountains, Colorado
• Date: 3/1/1976
• State: CO
• Weather Modification - Doc Type: Report

+.10
+.08 x X
+.06 0
0
X
+.04 A
+.02 A >>
A
(mean) 0
-.02 0
-.04
-.06
-.08
-.10
Tree-Ring Sites
SJS I - A
SJS 2 - 0
SJS 3- X
T.IO
....08
+.06
+.04 0
+.02 A
("!ean) 0 0
-.02 X l(
~
-.04 0 A
-.06 X
-.08
-.10
Summer Winter Spring Summer
(Jly.,Aug., (Nov., Dec., (Mar.,Apr.~ (Jly.,Aug.,
I Sep.,Oct.) ... Jan.,Feb.) I I May,Jun. ... Sep.,Oct.) I
Prior to Growing Growing
Season Year

PRECIPITATION

TEMPERATURE

Figure 6.

Serial regression coefficients for SJS-1, SJS-2, and SJS-3 for Durango seasonal precipitation
and mean seasonal temperature.

the results of the stepwise multiple regression
that its variance is due to other than climatic
factors (as recorded in Durango).

A dendroclimatic evaluation of historical climate
and a prediction of tree growth response were
attempted.

-Historical Climate

Using tree growth layer measurements for 1941-1945,
1951-1955, and 1961-1965 and the prediction
formulae the climatic trend was approximated and
supported when compared to the actual climatic
record.

-Prediction Of Tree Growth Response

Using the prediction formulae with the climatic
data for 1971, 1972, and 1973 the-tree growth
ranges of each of these years in stations SJS-1
and SJS-2 were projected. This was followed by
measurements of tree growth. The two agreed
remarkably within the confidence limits.

In general, stations SJS-1 and SJS-2 appear to be the
best indicators of change and possibly could be used
to monitor any future weather modification in the
area. This is not to say that changes due to weather
modification have been detected. Rather the tree

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growth response is correlating with the recorded
data. No significant departure in actual growth
response from the predicted growth response has been
noted. This indicates the general climatic trend of
the coring sites is paralleling the climatic trend
of the recording station, and the soil moisture regime
has not been altered. This could be interpreted as
the growth response of the trees has not been sig-
nificantly affected by the extent of this
weather modification program. However, the success
in predicting growth increments when compared to
actual growth tends to discount this possible
interpretation. Two possibilities remain: 1) the
coring sites are outside of the target area, or
2) weather modification has not altered the climatic
regime of the coring sites. The investigators can-
not state which is correct because of a lack of
climatic data near the coring sites.

Summary

Historical climatological data and tree ring
chronologies from three sites within the San Juan
study area have been used in the development of
regression models for the prediction of annual
tree growth increments. The general approach of
the study involved the application of two such
models based on climatological data from a site out-
side of the target area, to predict values of tree
growth increments for the years after the initiation
of the snow augmentation project. Since the tree

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