WMOD00385

• Title: Augmentation Potential through Weather Modification - Working Document
• Date: 2/1/1975
• Weather Modification - Doc Type: Report

HISTORIC POTENTIAL STREAMFLOW INCREASES IN 12
MAJOR WESTERN RIVER BASINS FOR THE 1952-1971 PERIOD

During the 13 years in which the Bureau of Reclamation has sponsored
weather modification research programs, a major goal has been to d,eter-
mine the feasibility of increasing water resources by weather modifica-
tion on an operational basis. The Twelve Basin Investigation was ini-
tiated to determine the potential increases in precipitation and
streamflow resulting from modification of cold orographic clouds in
both dry and wet years, taking into account the frequency of cloud seed-
ing. The seeding effects have been related to key airmass parameters
fr~m rawinsonde data and mountain precipitation records.

The investigation was conducted in the following 12 major river basins
of the Western United States:

~

l. Upper Colorado 7. Snake
2. Rio Grande 8. Upper Missouri
3. Truckee, Humboldt, and Walker 9. San Joaquin
4. Sacramento 10. Deschutes
5. North Platte 11. Bear-Wasatch
6. Gila 12. Yakima

Principal boundaries of these basins, the stream gaging st~ti9ns selected
for runoff analysis, and rawinsonde sites are shown on figure 1. Poten-
tial increases were determined as an average and on a seasonal bas~s for
the period 1952-1971.

Procedure for Identifying Increased Precipitation

The approach to identification of potential precipitation increases in
the Twelve Basin Investigation was the employment of a clo~d seeding model
for the development of precipitation-temperature diagrams based upon his-
torical precipitation and rawinsonde data. From such sets of curves, the
seeding potential was then determined.

".

The model used was an area of effect model which requires detailed upwind
sounding data, terrain features, and seeding source data (natural qr
artificial), and cloud top data or estimates. The area of effect ~odel
discriminates the potential for seeding increases in the diffefences
between calculated seeded and not seeded precipitation rates, based on
the detailed sounding data and observed hourly precipitation data. The
finer precipitation-aerological parameter (cloud tops, bases, etc.) rela-
tionships possible using hourly precipitation data led to the selection
of the area of effect model (with modifications) for the analysis in the
Twelve Basin Investigation.

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