Santa Ana River Watershed Cloud Seeding Program Update

The Santa Ana Watershed Project Authority (SAWPA) has concluded the first year of its planned four-year Santa Ana River Watershed Cloud Seeding Pilot Program.  The first year of cloud seeding began in November of 2023 and officially ended on April 15, 2024.  All of the cloud seeding for this project was conducted using ground-based equipment that dispersed vaporized silver iodide into storm clouds.  No aircraft-based cloud seeding was utilized.

Very preliminary data from a validation study carried out by the Desert Research Institute indicate the cloud seeding may have resulted in about 11,000 acre feet of additional precipitation in the target areas of the Santa Ana, San Gabriel, San Bernardino and San Jacinto mountains, and significantly, that the seeding did not appear to diminish precipitation down wind of the target areas.

As part of the validation study, snow samples from storms that were seeded were collected and analyzed for the presence of silver to help document whether the program was, in fact, producing snow in the desired areas.  Again, very preliminary results indicate the program was successful in producing precipitation in the form of snow.    In this study, falling snow was collected in sterile plastic bags before it hit the ground.  The snow was kept frozen while it was transported back to a clean lab, where it was melted and tested for silver using mass spectrometry.

A concern of the pilot program was to avoid seeding storms that were already very heavy or in areas where flooding or landslides were of concern.  To this end some storms were not seeded and in some other storms only a portion of the ground based seeding equipment was operated.  

Following the three large fires in our local mountains a decision was made to postpone the second year of the pilot program to the winter of 2025-26 to avoid any possible impact on the burn scars from those fires.  A decision on whether to operate the program in the winter of 2025-26 will be made as we get closer to the date.  This decision was made in consultation with the Orange, Riverside and Riverside County Flood Control Districts.

Happy New Water Year
The 2024-25 water year began October 1.  California ended the 2023-24 water year with more than typical amounts of water in storage both above and below ground due to back-to-back wet years and increased efforts to place excess water in underground storage.  Our surface reservoir storage is in good shape.  Diamond Valley Lake, which is the point where Western Municipal Water District gets most of its water for retail and wholesale customers, is currently at 97% of its capacity, which is 132% of normal for this date.  Riverside Public Utilities currently uses local groundwater for all its potable water needs, but should they need supplemental imported water, it would come through Western Water from Diamond Valley Lake.

The Department of Water Resources believes there is a 71% chance of La Nina conditions developing this fall.  Seventy percent of the La Nina events in the last century resulted in drier than average years, but they almost always result in wide swings from wet to dry within an individual year.  Overall, California is well situated for a two or even three year drought, but a longer one would be problematic.

Governor Vetoes Water Planning Bill
I had written previously about SB 366, a bill that would have required the Department of Water Resources to develop a plan to produce 9 million acre-feet of additional water supply by 2040 and to identify additional goals by 2050.  The bill had wide support and passed both houses of the legislature without a single no vote.  It was widely believed the Governor would not only sign the bill but perhaps make it a leading part of his water plan for the state.  To the surprise of many, the Governor elected to veto the bill, saying it had ongoing unbudgeted costs.  Proponents of the bill are considering next steps and may bring it back next year.