WMOD00432

• Title: Colorado River Augmentation Demonstration Program - Finding of No Significant Impact
• Date: 9/1/1985
• Weather Modification - Doc Type: Report

The effects from the programmatic alternatives are discussed at
length in the Project Skywater Final Environmental Statement (Bureau
of Reclamation, 1977), and tile reaoer is directerl to that document
for the detail s of short- and long-term effects of these alter-
natives.

C. Proposed Action

1. Cl imate

.

The region is distant from major sources of moisture, the air masses
cross numerous mountain ranges en route to the areas, and precipita-
tion is therefore sparse except in high mountain areas. For example,
average winter precipitation ranges from 30 inches on Grand Mesa to
less than 8 inches at Cedaredge, just 10 miles to the south at an
elevation of 6100 feet.

Summer precipitation contributes only a very small portion of water
to the Upper Colorado River Basin. While summer afternoon showers
are frequent, the amounts are often small and the localized runoff
seldom reaches main drainage streams. Most summer precipitation
supplies moisture to the evapotranspiration process.

About 75 percent of the runoff in the Upper Colorado River Basin
occurs from the melting of the winter snowpack, generally from areas
above 9500 feet in elevation. Approximately 50 percent of the winter
days have snowfall at elevations above 9000 to 10,000 feet, although
such things as site exposure and location with reference to other
barriers cause less frequency of precipitation at some high elevation
sites. Snowfall intensity is generally light. About one-half of the
total snowfall accumulation is produced on 15 percent of the heaviest
snowfall days. The difference between a wetter (or drier) than nor-
mal winter season is due to the occurrence (or non-occurrence) of a
few large storms that produce about 15 to 20 days of additional pre-
cipitation. Details of climate in the Upper Colorado River Basin can
be found in Klazura (1983).

Impacts. - Since the proposed action is for a research-level
program and cloud seerling would be considerably limited in extent and
duration, no significant effects would be anticipated on the climate
of Grand Mesa or the surrounding area.

:;.

2. Water Resources

"

The precipitation that enters Grano Mesa streams and reservoirs as
runoff is collected primarily from areas located at elevations above
9000 feet, with very litt.le runoff coming from lower elevations.

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