WMOD00476

• Project Name: Colorado River Basin Pilot Project
• Title: Executive Summary of Comprehensive Evaluation
• Date: 12/1/1976
• Weather Modification - Doc Type: Report

3. OPERATIONAL POTENTIAL

Two seeding strategies were analyzed to obtain the potential precipita-
tion increase. Strategy I involves seeding only stable, warm-topped clouds.
Strategy II involves seeding them and also stable cold-topped clouds when winds
are light enough to permit snowflakes to fall where desired. In each case, the
unstable clouds are not treated because seeding might actually decrease pre-
cipitation. Table 1 lists the separ~te zones within which data from groups
of monitoring stations in each zone have been averaged. Also given are per-
centage increases determined from the diagnostic analysis, after stratification
of data corrected by regression-type covariate analysis.

Increases of 61 to 120 percent are obtainable from Strategy I for warm,
stable clouds alone. Over the entire winter season, seeding only these clouds
would produce an overall seasonal increase of 8 to 11 percent. In Strategy II,
seeding only light wind, cold-topped, stable clouds along with all warm top
clouds produces increases of 67 to 98 percent. However, the addition of this
subcategory of stable cold clouds increases the number of suitable clouds so
much that the overall seasonal increase would climb to 10.5 to 12.5 percent.
The potential assumes that operations are flawlessly carried out, with no sus-
pensions or other restrictions.

These figures were translated into average precipitation increase during
the snow accumulation season from October 15 to May 15, and put into the
hydrologic streamflow model developed as part of this evaluation. The net
result is a potential increase in annual runoff of the San Juan River (inflow
to Navajo Reservoir) of 150 million m3 (122,000 acre feet) for Strategy I and
197 million m3 (l59,OOO acre feet) for Strategy II. In the Rio Grande Basin,
on the downwind side of the crest, the potential increase in annual runoff
(at Cochiti) is l73 million m3 (140,000 acre feet) for Strategy I and 186
million m3 (151,000 acre feet) for Strategy II.

Thus, Strategy II offers a potential increase in annual runoff of about
19% or 383 million ~3 (311,000 acre feet). This additional water could be
used to irrigate 75-100,000 acres of new farm land or serve the water needs
for a city of over one million people.

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