Arizona Cloud Seeding Efforts: A Salt River Project Perspective James Walter SRP Surface Water Resources
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 2
Winter Precipitation 3
Winter Precipitation 4
Winter Cloud Seeding 101 Bergeron Process 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 5
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 6
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 7
Winter Cloud Seeding 101? Source: North American Weather Modification Council 8
Early Cloud Seeding Projects 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 9
Early Cloud Seeding Projects 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) 10
Early Cloud Seeding Projects 11
Early Cloud Seeding Projects Source: AZ Republic, April 12, 1952 12
Questions and Concerns 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 13
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 14
Era of Research 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 Source: Twelve Basin Investigation, Vols. I and II. 1973 15
Era of Research 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 Source: Winter Cloud Seeding Potential On The Mogollon Rim: Final Report. 1989 16
Era of Research The Arizona Project 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 Source: Klimowski et al 1998 17
Recent Advancements Source: The Wyoming Weather Modification Pilot Project: Executive Summary. 2014 18
Recent Advancements Source: Rasmussen et al 2015 19
Recent Advancements Source: French et al 2018 20
Arizona s Current Interests and Activities 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. 21
Arizona s Current Interests and Activities 22
Arizona s Current Interests and Activities White Mts. 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) 23
SRP s Current Interests and Activities Continue monitoring research and cloud seeding activities Build partnerships Cloud seeding climatology study using latest models Feasibility study 24
QUESTIONS 25