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
CPWAC/CPWP Joint Meeting
March 30, 20183
Winter Precipitation
CPWAC/CPWP Joint Meeting
March 30, 20184
Winter Precipitation
CPWAC/CPWP Joint Meeting
March 30, 20185
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
CPWAC/CPWP Joint Meeting
March 30, 20186
Winter Cloud Seeding 101
• 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
CPWAC/CPWP Joint Meeting
March 30, 20187
Winter Cloud Seeding 101
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
CPWAC/CPWP Joint Meeting
March 30, 20188
Winter Cloud Seeding 101
?
Source: North American Weather Modification Council
CPWAC/CPWP Joint Meeting
March 30, 20189
• 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
CPWAC/CPWP Joint Meeting
March 30, 201810
• 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)
Early Cloud Seeding Projects
CPWAC/CPWP Joint Meeting
March 30, 201811
Early Cloud Seeding Projects
CPWAC/CPWP Joint Meeting
March 30, 201812
Early Cloud Seeding Projects
Source: AZ Republic, April 12, 1952
CPWAC/CPWP Joint Meeting
March 30, 201813
• 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
CPWAC/CPWP Joint Meeting
March 30, 201814
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
CPWAC/CPWP Joint Meeting
March 30, 201815
• 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
CPWAC/CPWP Joint Meeting
March 30, 201816
• 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
CPWAC/CPWP Joint Meeting
March 30, 201817
• 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
CPWAC/CPWP Joint Meeting
March 30, 201818
Recent Advancements
Source: The Wyoming Weather Modification Pilot Project: Executive
Summary. 2014
CPWAC/CPWP Joint Meeting
March 30, 201819
Recent Advancements
Source: Rasmussen et al 2015
CPWAC/CPWP Joint Meeting
March 30, 201820
Recent Advancements
Source: French et al 2018
CPWAC/CPWP Joint Meeting
March 30, 201821
• 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
CPWAC/CPWP Joint Meeting
March 30, 201822
Arizona’s Current Interests and Activities
CPWAC/CPWP Joint Meeting
March 30, 201823
Arizona’s Current Interests and Activities
…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.
CPWAC/CPWP Joint Meeting
March 30, 201824
• Continue monitoring research
and cloud seeding activities
• Build partnerships
SRP’s Current Interests and Activities
• Cloud seeding climatology
study – using latest models
• Feasibility study
CPWAC/CPWP Joint Meeting
March 30, 201825
QUESTIONS