WSP08775

• File Number: 8056
• Description: Drought Preparedness
• State: CO
• Basin: Statewide
• Date: 1/1/1979
• Author: USGS
• Title: Hydrologic and Human aspects of the 1976-77 Drought
• Water Supply Pro - Doc Type: Report/Study

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CHRONOLOGY OF THE 1976-77 DROUGHT

43

content of the poor snow pack in 1977 ranged
from 20 to 45 percent of normal in March,
April and May.
Below normal runoff occurred in all but one
or two months in periods as long as 18 months,
and flows were generally less than those in
1934. New low records were set for daily,
monthly, and annual flows. Storage in reser-
voirs was severely reduced.
Withdrawals of ground water increased by
as much as 60 percent, many new wells were
drilled, and water levels declined in several
areas. Changes in water quality of either
ground water or surface water were not
significant. Water use was restricted in
several communities.
The Upper Colorado Region was affected
by drought from 1931-35. The effect was
more pronounced in the lower part of the
Colorado Plateau and in the Gunnison River
valley in Colorado southeast of Grand Junction
than in the San Juan River basin (Thomas and
others, 1963d).
The average precipitation in Colorado and
in Utah for the 5-year drought was 85 percent
of normal. That for 1934 was 66 percent of
normal in Colorado and 74 percent in Utah.
The year 1933 was the warmest in 32 years in
Colorado, but 1934 was even warmer with an
unusual departure of plus 4.5oF. A similar
departure was observed in Utah.

Precipitation and Runoff

Precipitation during 1975 was slightly be-
low normal in the lower part of the region and
normal to about 115 percent of normal in the
upper part of the region. Monthly pre-
cipitation in 1976 exhibited a continually
changing pattern ranging from less than 50
percent to more than 150 percent of normal
for one month or another over most of the
region. The lower values started to be typical
of larger parts of the region in September 1976
and were representative of most of the region
by December 1976.
The below normal pattern of precipitation
that started in the latter months of 1976 con-
tinued over most of the region through Febru-
ary 1977. Some slight relief occurred in March
1977 when precipitation was above normal in
the upper Green River basin, but the total
precipitation for the month was small, less
than about 3 in. The drought conditions

.

became more severe in April when precipita-
tion ranged from about 40 to 75 percent of
normal. Additional precipitation in May im-
proved the situation, but it deteriorated again
in June. During the rest of the year precipita-
tion vacillated above and below normal over
most of the region.
The snowpack was poor in the eastern third
of Utah where the water content on March 1,
1977 was 20 percent or less of normal except
in the Fremont River drainage, south of Price,
where the water content was about 50 percent
of normal. By March 1, the snow water
content should be about 87 percent of the total
for the season.
Of the 82 snow courses in Colorado, 8 were
bare and 15 had less than 5 in. of water on
May 1, 1976. Comparable figures for 1977 are
38 bare and 23 with less than 5 in. of water.
Based on 76 snow courses, the water content
of the snowpack on April 1, 1976 was 99
percent of average and that in 1977 was 45
percent of average. The remains of the light
snowpack in Colorado in 1977 were only at the
higher elevations by early May and had only 21
percent of the normal water content. What
snow had melted sustained streamflow at only
about 50 percent of normal.
The difference in the areal extent of the
snowpacl< in part of the Upper Colorado River
and the Upper Missouri River basin between
1976 and 1977 is depicted in figure 17. The
snow cover in April 1976 is shown in figure
17a, and that in April 1977 is shown in figure
17b. The photographs were obtained from
Landsat satellite imagery and cover an area
approximately 115 mi on a side.
Steamboat Springs and Rabbit Ears Pass,
Colo., are near the center, the White River
basin is near the lower left corner, the Yampa
River is in the left center, the North Platte
River valley is between the north-south trend-
ing ranges of the continental divide and the
Medicine Bow Mountains in the upper right
quadrant, and the headwaters of the Laramie
River in Wyoming are near the upper right
corner.
Monthly flows at two index stations in
western Colorado, the Animas River at Dur-
ango, south of Grand Junction, and the Yampa
River at Steamboat Springs, indicate the
severity of the drought. Monthly flows of the
Animas River dropped below normal in Novem-
ber 1976, and except for August and Septem-