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

Table 6. Serial regression coefficients used in prediction equations
Site a Var b Var c Var d Var C
summer
prior winter spring summer
SJS-l +.0166 precip +.0317 precip +.0406 precip +.0001 precip 1.3854
SJS-2 -.0177 same +.0671 same +.0592 same +.0243 same 1.3291
SJS-3 +.0499 same -.0789 same +.0840 same +.0250 same 2.1537
Equation for above coefficients:
Annual tree ring width = a(x -x ) + b(xb-xb) + c(xc-xc) + d(xd-xd) + C (2)
a a
Where: a, b, c, and d are regression coefficients

xa' xb' xc' xd are seasonal precipitation totals for the growth year
- - - -

xa' ~, xc' xd are mean seasonal precipitation values
C(onstant) is the mean ring width

Table 7. Predictions of tree ring widths (mm) for 1971, 1972 and 1973 from equations in Tables 5 and 6
Equation 1 Equation 2
Predict S.E. Actuala Resid. Predict Actual Resid.
SJS-l 1971 1. 20 1.16 + .04 1.02 1.16 - .14
1972 1.21 + .32 1.84 - .63 1. 24 1.84 - .60
1973 1.37 1. 35 + .02 1.25 1. 35 - .10
SJS-2 1971 2.32 .99 +1.33 1.96 .99 .97
1972 2.48 +- .49 1.03 +1.45 2.47 1.03 +1.44
1973 2.71 .77 +1. 94 2.63 .77 +1.86
SJS-3 1971 4.48 1.07 +3.41 3.22 1. 07 +2.15
1972 4.65 +1. 58 1.36 +3.29 3.88 1.36 +2.46
1973 5.53 1.08 +4.45 6.35 1.08 +5.27

aAdd +0.10 mm, the estimated error of measurement.

ring sites are within an area which theoretically
is being subjected to a change in moisture regime
due to cloud seeding effects; a significant diff-
erence between predicted and actual annual tree ring
growth increments would be interpreted as evidence
of this change in climate. A major handicap in the
application of this method to the San Juan Ecology
Project is the small sample of post-seeding cases.

The experimental design is based on four categories
of data: tree growth within the target area, tree.
growth outside the target area, climatic data within
the target area, and climatic data outside the target
area. Correlation analyses of climatic data as the
dependent variable are done for the period prior to
weather modification. Using the results of each of
four multiple stepwise regressions, tree growth ranges
are predicted within the target area and outside the
target area. The climatic data used in the prediction
formula is for the period of weather modification.
The actual growth responses are then compared with
the predicted ranges.

Correlations of tree data and climatic data from
within a target area and from outside the target
area may lead to a system to:

a. determine which climatic parameters have
had the greater influence on tree growth;

b. determine the. degree of influence by each
parameter;

c. determine the collective influence of these
climatic parameters in an interacting
system;

d. predict tree growth during the period of
weather modification as a means of detecting
whether there is or is not an influence due
to weather modification; and

e. evaluate the degree of influence if any
is detectable.

Because this process approach is based on a model of
interacting parameters, several assumptions must
be made.

a. A responsive tree species showing a variable
growth sequence is located in the area.
Most species of pine are good for this
purpose.

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