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

monthly data into meaningful categories for the
growth response of trees in the final detailed
analyses. Parallel trends indicate a direct re-
lationship of growth layer thickness with the
climatic factor. Opposite trends indicate an
inverse relationship of growth layer thickness with
the climatic factor.

A sample of the results from the trend method is
given for monthly precipitation using six recording
stations and one coring station for 15 months
(Table 2). Only the trend coefficient is included
but the preliminary evaluation also considered the
index values and ratios. From the data sets the
Durango and Pagosa Springs weather records w~re
selected for use in subsequent analysis. Pagosa
Springs correlations are high and relatively
consistent.

The complete trend analysis for monthly precipi-
tation from the Pagosa Springs weather station with
tree ring data from station SJS-1 is given in
Table 3. For the previous December precipitation,
the variation is mainly parallel and highly corre-
lated. For August precipitation, the amplitude of
opposite trends is greater than that of parallel
trends.

The results of this preliminary evaluation provided
a means for the selection of potentially important
monthly data of precipitation and temperature for
more detailed analysis. Pagosa Springs and Durango
weather data sets were chosen and specific groupings
of monthly data were selected.

-Descriptive Statistics

Table 4 presents the means and standard deviations of
tree ring widths for each study site and for each of
the three time spans corresponding to the period
of record for the climatic stations. In addition
the correlation coefficients between the tree rin~
chronologies for the three study sites are presented
for each time span.

For the period 1896-1970, the time period used in
the bulk of the analysis, growth layer widths at
SJS-1 and SJS-2 have a correlation coefficient of
0.18. This lack of regional correlation indicates
that the climatic environment may not be uniformly
represented by the tree ring sequence exhibited by
the three study plots. This emphasizes the need
in size selection for near-optimum or relatively
dry sites for studies of this nature. Station SJS-3
has a relatively high and uniform soil moisture
throughout the year and is not characteristic of
the area as a whole.

-Detailed Analysis

Two parametric statistical approaches were used in
the final phase of the data analysis: stepwise
multiple regressio~and bivariate techniques in-
cluding the calculation of serial regression co-
efficients. Individual monthly temperature and
precipitation values, as well as seasonal aggre-
gates of these figures, served as independent vari-
ables in the regression analysis.

Table 2. Summary (trend coefficient) of preliminary analyses using the trend method for precipitation
with tree growth of station SJS-l.
Preceding Growing Season
July Aug. Sept.
Ouray 0 + 0
-Lake City 0 +
Telluride 0 0 0
Durango 0
Pagosa Springs +(.51) +
Silverton 0
Winter Prior to Growing Season
Oct. Nov. Dec. Jan. Feb. March
Ouray 0 +(.53) +(.49 ) +(.89)
Lake City +(.61) + +(.46) +.49) +(.65)
Telluride 0 + +(.57) + + +
Durango 0 + +(.53) +.59) 0 +
Pagosa Springs 0 + +(.91) + ( . 68) + +(.62)
Si1verton + +(.48) +(.61) + 0
During Growing Season
April May June July Aug. Sept.
Ouray + 0 0 0 - (.64) +
Lake City 0 +(.54 ) 0 0 0 0
Telluride 0 0 0 0 + 0
Durango + + +(.66) + 0 0
Pagosa Springs 0 +(.58) 0 -(.73) +
Si1verton 0 + + 0 + +

,

0=</.25/

+ = >/.25/ < /.50/

Value when> / . 50/

Length of record used (years): Ouray 23 (1943-1966); Lake City 61 (1905-1966); Telluride 55 (1911-1966);
Durango 72 (1894-1966); Pagosa Springs 27 (1939-1966); Si1verton 60 (1906-1966).

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