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

Roger

HISTORICAL CLIMATOLOGY l/
2/
G. Barry - and Raymond S. Bradley

ABSTRACT

Historical climatological data for the San Juan area
have been examined for the purpose of assessing the
regional climate of the last century. This effort
provides an information base with which to compare
the records representing the 1970-75 winter snow
augmentation program.

Temperature fluctuations during the period indicate
regional cooling from the late 1860's until about
1930, when a reversal of the trend occurred. These
temperature trends are the opposite of those noted
for many areas in the Northern Hemisphere. Precipi-
tation variations tend to be inversely related to
temperature trends in the San Juan region.

An analysis of weather types affecting the area
indicated that most situations favorable to cloud
seeding have occurred during a small number of
broad-scale synoptic types. The historical record
shows that the monthly frequency of these types
varied considerably with the highest frequencies
near the beginning and end of the winter period, and
the lowest during the month of December.

Rapid transition between relatively dry and
relatively wet precipitation regimes is a feature
exhibited by several stations within the area. This
aspect of the climate should be considered if pre-
cipitation augmentation projects are to be resumed
in the San Juan region.

INTRODUCTION

"We often hear the statement made that the climate is
changing, and the popular belief that such is the
case can only be explained by the generally short
and defective memories of people who, through
exposure to a few severe storms in the past...
exaggerate the severity and frequency of their
occurrence. Although large fluctuations occur in
different years, especially in Colorado...there seems
to be no progressive change... In the meteorological
data of the last 100 years there is nothing to
support the idea of any permanent change in the
climate having taken place or that any change is
about to take place...and the mean temperature shows
no indication of any permanent change either warmer
or colder.... We often hear it stated that the rain-
fall is changing, that the settling up of the
country and the planting of trees and building of
reservoirs, forming lakes and wet places throughout
the country is causing an increase in the amount of
our precipitation, but long series of observations
taken at different places over the world do not bear
out that claim." (Trimble 1918)

The Historical Climatology Project is designed to
examine all available documentary material which may
be relevant to assessing climatic conditions in the
San Juan area over the last 100 years and hence to
provide a background against which the 1970-75

winter precipitation augmentation program can be
assessed. This involves two main tasks: examin-
ation of reports written by laymen in the area,
and analysis of climatic data kept by authorized
agencies.

Examination Of Lay Reports

Initially, visits were made to the State Historical
Society in Denver and the Center for Southwestern
Studies in Durango to determine the amount and
quality of information available from documentary
reports. Examination of pioneer reports, news-
papers, magazines, and historical data connected
with mining activities in the San Juan Mountains
all indicated that little useful information could
be obtained from such sources. References to climate
are frequently vague qualitative assessments and
occasionally written so as to encourage settlement
in the area:'

...its climate, in spite of its altitude,
owing to its southern latitude is free from
extreme cold and heat, malaria and disease,
and the insect and vermin of lower altitudes.
Though, owing to its altitude, snow falls
to a greater depth than anywhere else, its
inconvenience and annoyance is less
noticeable than four inches of freezing
and thawing mud at lower altitudes.
(Bruns 1897)

Occasionally, an event is noted which indicates in
a relative sense the magnitude of a climatic
event, e.g.

In 1885, there was the most snow on Cumbres
known until the past winter of 1931-32,
and no train got over the pass for three
months. (Cornelius 1933)

However, such events generally refer to the period
for which instrumental records have been kept and
therefore only reflect in a qualitative sense
events recorded quantitatively elsewhere. The
only weather diary found for the area was that
kept by Mr. Bill Davies in Durango from 1916-66 but
more comprehensive Weather Bureau records for the
city are available in a more accessible form.

Examination of Agency Data

Data on microfilm from the National Archives in
Washington, D.C. indicate that few climatological
records are available for useful lengths of time
prior to 1880 in the State of Colorado.

Army posts began regular observations in the 1820's,
but these ~ere principally restricted to the states
east of 95 W longitude. Data collection for western
states began in the 1850-1860 period by the U.S.
Army supplemented by individual observers under the
direction of the Smithsonian Institution and the

l/ In Steinhoff, Harold W. and Jack D. Ives (Eds.) 1976. Ecological Impacts of Snowpack Augmentation in
the San J~an Mountains, Colorado. San Juan Ecology Project, Final Report. Colorado State Univ. Publ.,
Fort Coll~ns.
~/ Present Address: INSTAAR, University of Colorado, Boulder, Colorado 80309.

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