Cloud seeding considered for California


The lack of rainfall has pushed California legislators to thinking about ways to help the state's water supply.

One way they're considering is a technique called cloud seeding.

The premise behind cloud seeding is essentially introducing a hydrophilic – or water attracting – substance to the clouds which will help to produce rain or snow.

The current leading material in cloud seeding is a substance called silver iodide.

It's used because its chemical structure is very similar to ice, which is the favored substance for other water molecules to condense onto.

Once the water molecules start to condense and form larger droplets a cascade effect occurs in which the droplets grow larger and heavier, eventually becoming rain and falling to earth.

There are three methods of distributing the silver iodide into the clouds, releasing it in the form of smoke, firing flares or rockets into clouds, or from flares attached to aircraft.

Many experiments have been done dating back to the 1970s testing both the theoretical feasibility of cloud seeding and the possible dangers that cloud seeding could pose to humans and the environment.

One study, published in the Journal of Water Resources Research, found that the iodine content of cloud-seeded rainfall is so low that you would need to drink 130 gallons of unfiltered rainwater to receive a dose equal to that of a few shakes of iodized table salt.

It went on to say that the silver contained in silver iodide will fall in an insoluble form and will not be the more dangerous ionic form of silver which can be toxic if it comes in contact with cell membranes.

In its normal state, silver does not act like other toxic heavy metals such as lead of mercury.

That same article states that even in its ionic state, silver is rapidly removed from the body by the liver.

Another study done by the Center of Disease Control entitled the NIOSH Health Hazard Evaluation Report from 2010 concluded that workers in a plant that built silver iodide flares for cloud seeding were not in danger of adverse health effects.

And the exposure levels experienced through precipitation due to seeded clouds would amount to a tiny fraction of the levels in the NIOSH evaluation report.

The only organisms that may be affected are microscopic soil bacteria and some fish.

But those same studies report that the affects of silver are greatly diminished as the affected water is washed farther downstream.

Most likely, the hardest hit organisms will be the bacteria involved in the decomposition of detritus at the bottom of lakes and ponds.

The California Department of Water Resources says the project could generate four hundred thousand more acre-feet of water through seeded clouds.

There are contradicting studies published by the American Meteorological Society which says that although seeded clouds create larger drops, the overall increase in total precipitation is largely negligible.

Simply stated, studies have found that the seeded clouds cause rain to fall harder, but don't create more rain.

Scientific American calls into question the effectiveness of cloud seeding as well when examining a snow storm in China.

But concluded that it was China's government trying to take credit for a natural phenomenon.