Can Humans Control The Clouds?
MADELEINE BRAND, host:
China is shooting a chemical agent into threatening clouds. It's doing that to bring on rain before the opening ceremonies to clear the air a bit.
ALEX CHADWICK, host:
So here in the U.S., Los Angeles county is also seeding clouds to help shore up record low rainfall. California has been in a drought officially since June.
BRAND: Though the hope is to get more rain, scientists say it's not a sure thing. Celeste Headlee reports.
CELESTE HEADLEE: Officials with Los Angeles county are very confident. Confident that cloud seeding works, and that it can increase rainfall by 15 percent in the area along the base of the San Gabriel mountains.
Mr. WILLIAM SAUNDERS (Water Resources Division, L.A. County): 15 percent in those watersheds represents 4,500 acre feet. That's 1.5 billion gallons.
HEADLEE: William Saunders is with the water resources division for L.A. county. Los Angeles actually started seeding its clouds in 1957, but the program was halted in 2002, when fires burned away a lot of the brush and ground cover, and there was danger of mudslides. Now, the clouds above L.A. county will again be filled with silver iodide in hopes it will create ice crystals that will fall to the ground as rain.
Mr. SAUNDERS: So the intent is to really reinitiate the program because we have the ability and to then carry on with it, if we can.
HEADLEE: Under natural conditions, sometimes only 20 percent of the water in a cloud will turn into rain or snow. Roelof Bruintjes of the National Center for Atmospheric Research says cloud seeding is designed to up that percentage, but it's not guaranteed.
Mr. ROELOF BRUINTJES (National Center for Atmospheric Research): Depending on the type of clouds you have in your region, depending on the type of pollution levels you have, cloud seeding may work better or may not work at all.
HEADLEE: Gabor Vali is professor emeritus at the University of Wyoming. He's studied cloud seeding for years. Vali says seeding is a bit like a brand-new prescription medication. There are positive indications and promising evidence, but no real clinical trial to prove it's effective. When you're testing clouds, which are, by their nature, unpredictable, you don't have a control group to compare results.
Dr. GABVOR VALI (Professor Emeritus, Atmospheric Science, University of Wyoming): In ideal situations, we know it can work, and there are some bits of evidence that such situations may sort of exist. But life is always more complicated than that, and clouds are extremely so.
HEADLEE: Cloud seeding is used all over the world. In fact, right now in Beijing, they're seeding clouds, hoping to clear out air pollution ahead of opening ceremonies. Some places report thundering successes. This spring, newspapers in Saudi Arabia reported that an unexpected thunderstorm there was caused by cloud seeding tests. Bruintjes says such claims are ridiculous.
Mr. BRUINTJES: Those are all - no scientific basis to them, and actually, they go against the laws of physics.
HEADLEE: Basically, Bruintjes says, you can't create clouds. You can only seed those that already exist.
Mr. BRUINTJES: You cannot make a big thunderstorm out of nothing. Neither can you make a big rainfall event out of nothing.
HEADLEE: That's why cloud seeding is not a drought-busting tool because in a drought, you have fewer clouds. But William Saunders says L.A. county's program isn't just meant to combat drought. He says it's a long-term strategy to increase water supply in the thirsty region. And he says they keep careful records to make sure cloud seeding is working.
Mr. SAUNDERS: We can determine what would be normal within a region, and then, using the amount of rainfall afterward, after we've cloud seeded, we can determine whether or not we've actually achieved our 15-percent objective.
HEADLEE: Over a four-year period, the cloud seeding program will cost about 800,000 dollars, and it will only be renewed if rainfall actually increases. Saunders says the county has more than a century of rainfall records to establish normal rainfall amounts.
Dr. VALI: No good. That game won't tell you anything.
HEADLEE: Gabor Vali says those records are mostly unreliable. And because weather systems vary widely from year to year, historical records aren't a conclusive measuring tool for rainfall. Even that 15 percent benchmark that Saunders is talking about is based on a rainfall study from the early 70s.
Dr. VALI: In principle, it looks like a promising and possibly rewarding thing to do, but they're taking a chance. First of all, it's certainly much less certain than other things they could do with that money.
HEADLEE: If the program does, in fact, increase rainfall by 15 percent in L.A. county, that works out to two million dollars they don't have to spend bringing water from the Colorado River. Vali says it's a good thing to increase water supply, but the surest and most economical solution, he says, is to simply conserve. For NPR News, I'm Celeste Headlee.
(Soundbite of song "It Never Rains (In Southern California)")
TONY! TONI! TONE!: (Singing) It never rains...
BRAND: It Never Rains (In Southern California), by Tony! Toni! Tone! You know, a few of you commented on our blog to tell us that is your favorite California song.
CHADWICK: If that's the favorite California song, what about the favorite California book?
BRAND: You can go to our blog: npr.org/daydreaming and check out some of our favorites and share some of yours.