When it rains in Santa Barbara County, it pours – but sometimes 15 to 20 percent more than nature intends, say county hydrologists.

Last week, the Santa Barbara County Board of Supervisors approved the continued funding of a cloud-seeding weather modification program, despite a recent report issued by the National Academy of Sciences questioning the technique’s effectiveness at inducing rain.

At a total cost of $250,000 for the 2003-2004 winter storm season, the county and other municipalities such as the city of Santa Barbara and the Goleta Valley Water District will fund the operations of North American Weather Consultants, Inc., a Utah-based company that specializes in rain augmentation techniques.

Cloud seeding is a scientifically controversial process that proponents say squeezes more rain from passing storm systems than would naturally occur otherwise. Opponents maintain there is little proof cloud seeding is consistently responsible for measurable rainfall gains.

The process uses airplanes and ground stations to disperse microscopic particles of silver iodide – the seed – into bands of moisture at particular temperatures and altitudes. If atmospheric conditions are correct, the particles of silver iodide will supplement existing dust particles in the air.

These dust particles, called condensation nuclei, are the bases upon which raindrops form. The purpose of seeding a cloud with more particles of condensation nuclei is to increase the amount of rainfall a given storm produces, often for purposes of drought relief or the refilling of reservoirs.

The chemical used to promote raindrop formation, silver iodide, is an inert, nontoxic substance that does not react with anything on the ground.

Proof of Effectiveness?

Cloud seeding has been used to augment rainfall in certain mountainous areas of Santa Barbara County for the past 16 years, said Dennis Gibbs, hydrologist and administrator of the county’s cloud seeding program. Operations take place between November and April, the height of the storm season.

Ground-based seeding stations spread along the county coastline release silver iodide into storms on their ways to the Cachuma Reservoir target area or the Huasna-Alamo target area. Seeding operations aim for these areas, which are near river headlands, to increase water flow to the reservoirs. Gibbs said seeding is not done over urban areas for safety and liability issues associated with possible flooding.

Gibbs, who has been involved in county cloud seeding efforts for 15 years, said he is convinced the process works, despite the findings of the National Academy of Sciences.

“I wish they had talked to us,” Gibbs said. “They generalized from cloud seeding data around the world.”

Gibbs said ocean-born storms are optimal for cloud seeding operations because they lack high levels of condensation nuclei, but have high levels of condensation. This makes it more likely that cloud seeding will work in Santa Barbara as opposed to other areas.

“The only real proof is statistical,” Gibbs said. “Studies to prove it unequivocally involve atmospheric modeling and research that is real expensive. We have applied for grants to prove it really works, but we haven’t gotten any.”

Gibbs said local cloud seeding effectiveness is determined by measuring rainfall in target areas versus adjacent, unseeded areas.

He said data from three separate research projects conducted in Santa Barbara County between 1950 and 1973, in addition to statistical analyses showing 15 to 20 percent increases in rainfall totals during several specific seasons during the 1980s and 1990s, proves the effectiveness of the program.

“The big picture for us is the water supply over the long term,” Gibbs said, noting that the county does not direct the cloud seeding contractor to measure rainfall totals every year.

Obstacles to Better Research

According to a National Academy of Sciences report released Oct. 13, human activities can affect weather and there is evidence that seeding causes changes within clouds.

“However, we still are unable to translate these induced changes into verifiable changes in rainfall … or to employ methods that produce credible, repeatable changes in precipitation,” the report states.

The report says that “in some instances there are strong indications of induced changes, but evidence has not been subjected to tests of significance and reproducibility.” The report calls for “sustained research of the underlying science” combined with physical and statistical experiments.

UCSB geography professor Hugo Loaiciga, a former member of the Santa Barbara Board of Water Commissioners – a group that advises the city council on water resource management issues, said he was not surprised that the National Academy of Sciences is skeptical of cloud seeding’s effectiveness.

“It’s very difficult to actually estimate effectiveness,” Loaiciga said. “The rainfall measurement data is provided by the contractor. When they give their numbers, I always have big questions. When I ask how they know, I’ve never really got intellectually satisfying answers.”

Loaiciga said a serious study of cloud seeding effectiveness could take five to ten years and cost somewhere “in the million dollar range.”

However, Loaiciga said that after spending $300,000 per year for 20 years, he thinks it might be worth it for the county to test the program’s effectiveness.

“But I don’t see that happening,” Loaiciga said. “Years later it might show [elected officials] have wasted a lot. Once programs are created, they don’t go away.”

Merits of the Program

Gibbs said the benefits of the county’s cloud seeding program justify the cost, given its relatively cheap price compared to the high cost of water from the state. Based on a 15 to 20 percent increase in rainfall and water collected in reservoirs as a result of cloud seeding, Gibbs said cloud seeding water only costs $150 per acre foot, as opposed to $1,200 per acre foot if purchased from the state.

“When you look at the volume of water, you have a cost-benefit ratio that is off the charts,” Gibbs said. “I really believe it’s a good program. [The water’s] cheap; it falls into our backyards and it uses existing infrastructure.”