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

Nineteenth Century Precipitation Data

The principal record for the 19th century is that of
Fort Massachusetts/Fort Garland on the eastern side
of the San Luis Valley, on the lower slopes of the
Sangre de Cristo Mountains. This record extends.
from 1852 to 1883 but is by no means complete.
Numerous problems of data interpretation exist. For
example, in some months precipitation values are
entered in cubic centimeters and in other months in
inches, but occasionally the values are not made
clear. Another difficulty arises in deciding when
observations were moved from Fort Massachusetts to
Fort Garland, since frequently the two names are
used interchangeably with the same location being
given for the station (Table 4). In view of the
change in observer and station name in August 1858,
it seems likely that the station location was moved
to a new site, the accurate position and elevation
of which was gradually ascertained and improved upon
over the subsequent 25 years. It thus seems reason-
able to assume the observations after 1858 represent
one site at Fort Garland. Figure 2 shows the annual
precipitation observations for the two Forts and
also includes data from Hermosa and Fort Lewis.
Doubtful values and those years with missing data
are indicated. By examining seasonal values the
problems of missing months can partly be offset. In
most cases, the missing data occur in the winter
months whereas summer and spring seasons are reason-
ably complete. An analysis of these seasonal values
suggests that the period 1863-72 was slightly drier
than the period 1873-82 for both summer and spring
periods (Figure 14). However, this does not
necessarily also apply to the winter months. The
Fort Lewis record indicates a rising trend of
precipitation up to the early 1890's when it would
appear that precipitation fell to the 1900-1901 low
already noted for other stations. It appears,

25

65

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1855 1860 65

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95 1900 1905

70

75

80 85

90

Figure 14. Nineteenth century records of annual
precipitation, 1858-1905. Solid line z
Fort Garland, dotted line = Hermosa,
small dashed line = Montrose, two dots
and dashed line = Fort Lewis, one dot
and dashed line = Durango, starred =
data of doubtful quality.

therefore, that precipitation may have followed a
rising trend from the 1860's to the 1890's followed
by a marked low period around the turn of the
century.

When seasonal fluctuations are examined, the records
indicate that the largest seasonal increases in
precipitation occurred during winter and summer
months.' At Fort Garland, for example, the mean
winter precipitation 1858-68 (6 years due to missing
data) is 2.7 cm (1.08 inches) and for 1873-1882
(10 years) is 6.9 cm (2.7 inches). In terms of
contemporary climate it has been suggested that
conditions in southern Colorado in the 1860's were
drier than, or at least as dryas, the period
1931-60 (Bradley and Barry 1973).

Table 4. Apparent changes in location and elevations of meteorological recording stations at Fort
Massachusetts and Fort Garland

Period Location Noted Elevation Station
(feet)
Oct 1852-Jul 1853 37030'N, 105040'W 8,000 Ft. Massachusetts
Aug 1853-Jul 1858 37031'59"N, 105040'W 8,100 Ft. Massachusetts
(no change in observer)
Aug 1858-Nov 1867 37031'59''N, 105040'W 8,100 Ft. Garland
(observer changes)
Dec 1867-0ct 1874 37022'N, 105023'W 8,365 Ft. Garland
(observer changes)
Nov 1874-Sep 1878 37023'N, 105027'W 7,681 Ft. Garland
(no change in observer)
Oct 1878-May 1879 37023'N, 105023'W 7,937 Ft. Garland
(no change in observer)
Jun 1879-0ct 1883 37022'N, 105023'W 7,937 Ft. Garland
(no change in observer)

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