Arizona Cloud Seeding Efforts: A Salt River Project ... seeding.pdf · Winter Cloud Seeding 101 1) –Air is forced up and over mountains and cools 2) –Moisture condenses and forms

James WalterSRP Surface Water Resources

CPWAC/CPWP Joint MeetingMarch 30, 2018

Arizona Cloud Seeding Efforts:A Salt River Project Perspective

CPWAC/CPWP Joint Meeting

March 30, 20182

• Importance of Winter Precipitation

• Winter Cloud Seeding 101

• Early Cloud Seeding Projects

• Questions and Concerns

• Era of Research

• Recent Advancements

• Arizona’s Current Interests and Activities


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Winter Precipitation


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Winter Precipitation


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Winter Cloud Seeding 101

• Cloud droplets (supercooled liquid water (SLW)) and

ice nuclei/crystals coexist in clouds with

temperatures between 0˚C and -40˚C

• Supercooled droplets can freeze on contact with ice

nuclei/crystals or supercooled water can transfer to

the ice nuclei/crystals (much like condensation) due

to physical properties of water and ice

• Cold clouds typically have more supercooled droplets

compared to ice nuclei/crystals

Bergeron Process


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• In 1946, General Electric scientists working in a lab were able to

increase the number of ice crystals in a cloud by introducing dry ice to

the cloud

• Lab results were successfully transferred to the natural environment

• Soon began to speculate that other substances might convert SLW to

ice

• Finally, they discovered that a silver iodide smoke was more effective

at creating ice crystals due to an increase in the number of silver

iodide particles introduced into the ice chest


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1) – Air is forced up and over mountains and cools

2) – Moisture condenses and forms a cloud with cloud

drops remaining liquid even in sub freezing temperatures

(super cooled liquid water – SLW)

3) – Ice and dust particles act as nuclei for SLW and

freeze.

4) – Additional SLW freeze onto the ice forming a snow

flake

Source: North American Weather Modification Council


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?

Source: North American Weather Modification Council


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• The Arizona Republic, Phoenix Junior College, and Irving Langmuir

developed a cloud seeding pilot project

• The first pilot project took place during July and August, 1947 when the

Arizona Republic chartered a DC3 and began dropping dry ice into

cumulus clouds on the Salt and Verde watersheds

• Visual observations indicated that rain was being created, but rainfall

measurements and photography failed to validate the experiments

Early Cloud Seeding Projects


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• Estimated benefits of cloud seeding began to be hypothesized by many

• Irving Langmuir suggested a 2 to 3 fold increase in precipitation with hopes

of ending the drought

• Others suggested a 4 fold increase resulting in 2 million acre-feet of runoff

annually (more than double the annual inflow into the Salt and Verde

system)



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Source: AZ Republic, April 12, 1952


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• Results over the Salt and Verde watersheds were inconclusive, less than

advertised, and could not be differentiated from natural occurrences

• Similar results were found over southern Arizona by Dr. Battan when

seeding summer thunderstorms

• Drought conditions ended over Arizona

Questions and Concerns


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Questions and Concerns

“It must be noted that the inflated claims of certain of the

contractors of the day left governmental officials farmers,

and cattlemen skeptical, if not actually hostile, to

attempts at reviving the program.”

- R E Moore

Source: Moore, R. E., 1971: Weather Modification in Arizona, The Current Outlook.

Southern Great Plains Weather Modification Conference, Oklahoma City, OK.

Personal Letter from Governor J. Williams to R. E. Moore (SRP), 1972


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• In the 1970’s results from initial USBR research projects

across the Western US suggest the potential for

precipitation enhancement over the Mogollon Rim of

Arizona

• SRP’s interest grew, joining the North American Interstate

Weather Modification Council and began to participate in

cloud seeding research with the USBR

Era of Research

Source: Twelve Basin Investigation, Vols. I and II. 1973


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• During the 1980’s the USBR, ADWR, SRP, North American Weather Consultants, and University of Wyoming

funded and performed additional research including field work over the Mogollon Rim

• Results indicated SLW was available for seeding with quantities and timing being variable

• Aircraft seeding most promising as opposed to ground based seeding

• Studies all suggested additional research was needed

Era of Research

Source: Winter Cloud Seeding Potential On The Mogollon Rim: Final

Report. 1989


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• NOAA funding to University of Arizona and NCAR in the

early 1990’s lead to the development of high resolution

weather modeling

• Modeled conditions looked ripe for airborne cloud seeding

• 1995 The Arizona Project was sponsored by the University

of Arizona with participation from ADWR, NCAR, NOAA,

NASA, Emery-Riddle University, ASU, U of WY, NAU,

USFS, SRP, and others

• Results indicated

• large amounts of SLW exist in the atmospheric

mountain wave and in orographic upslope flow

• sizable increases in radar reflectivity during seeded

events

• Airborne seeding was affective

• Ground based seeding only effective for a limited

number of cases

Era of Research

The Arizona Project

Source: Klimowski et al 1998


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Recent Advancements

Source: The Wyoming Weather Modification Pilot Project: Executive

Summary. 2014


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Recent Advancements

Source: Rasmussen et al 2015


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Recent Advancements

Source: French et al 2018


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• CAP (along with Southern Nevada Water Authority and the Six Agency

Committee of California) have been co-funding the operational cost of the

cloud seeding programs in the Upper Colorado River Basin states of

Colorado, Wyoming, and Utah.

• CAP has spent over one million dollars since 2007 on cloud seeding activities

in the Upper Colorado River Basin.

• CAP is also a member of the North American Weather Modification Council.

Arizona’s Current Interests and Activities


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…the use of model reanalysis datasets or high resolution regional climate model

output to study the climatology of seeding conditions over mountain barriers where

observations are limited has been instrumental in evaluating the fraction of winter

storms that are “seedable.” (Teesndorf et. al. 2015)

White Mts.


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• Continue monitoring research

and cloud seeding activities

• Build partnerships

SRP’s Current Interests and Activities

• Cloud seeding climatology

study – using latest models

• Feasibility study


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QUESTIONS

Documents

Arizona Cloud Seeding Efforts: A Salt River Project ... seeding.pdf · Winter Cloud Seeding 101 1) –Air is forced up and over mountains and cools 2) –Moisture condenses and forms