How to Make It Rain (when you can't do the dance)

A legal notice in Sunday's Midland Reporter Telegram gave notice that West Texas Weather Modification Association, which has been conducting cloud seeding operations around San Angelo, Texas, for several years, has filed an application for a four year permit to let it try to help keep the rains coming.

How will they do that?  From the notice:

"The aircraft will be equipped with flare racks and/or generators to dispense appropriate materials, either glaciogenic or hygroscopic or a combination of the two, into those clouds deemed receptive to seeding."

One method of making rain is to cause the moisture in clouds to freeze into droplets that become heavy enough to overcome the pressure in the cloud and fall, thawing on the way down, to become rain.  A glaciogenic substance would help stimulate the freezing of the moisture.  Source.

Silver iodide is such a substance as it has a structure similar to ice, and when it's present it helps induce the freezing of the water droplets.  But, the clouds have to contain super cooled water (zero degrees Celsius or lower), so conditions have to be just right before it will work, and it takes some very accurate meteorological information to know when those conditions exist.  Source.

The process also might suppress hail.  Source.

Hygroscopic seeding is the introduction of salts into the clouds.  The salts help transform water vapor into liquid water though the process known as vapor deposition.   Follow the link for details on some experiments and examples, such as a South African paper mill producing effluent of extra large hygroscopic particles which seemed to be causing extra large rain drops.  Splat!

How successful is cloud seeding?  According to the state licensing site, "It cannot be overstated that drought is not the optimal time period for cloud seeding."  However, they estimate that in the year 2003 cloud seeding produced 2.8 million acre feet of rain water in Texas over what might have been otherwise produced by the clouds had they not been seeded.

Doing the math:  There are 640 acres in a square mile, therefore 2,800,000 acre feet of water would cover 4,375 square miles with water one foot deep.  That would cover entire the state of Rhode Island (1,545 square miles) with almost three feet of water.

And finally, the most important question:  How much does it cost?

At one section of the Texas Department of Licensing and Regulation site the TDLR estimates that the cost is 4 to 5 cents per acre of land expected to receive the rain, an area that could cover 6.4 million acres at the San Angelo project.  However, elsewhere at the same site the TDLR estimates the cost to be 8 to 9 cents per acre.  Using the highest estimate it comes to just over a half million dollars for that project.

Not cheap.  But maybe it's worth the price if the alternative is to dry up and blow away.

Comments

[benning]

Interesting! I hope they succeed! Cosy may be unimportant if they can do it. I wonder if it will improve the flavor of the water there?

The odd thing is that I don't hear the name San Angelo very often. I spent a few nice weeks there with a lovely lady a few years ago. I liked San Angelo, though it was a pain getting liquor - dry county? Yeesh!

Saw Fort Concho, the old Bordello - the town is a neat place to see, not to mention a college town, too. Had a nice seafood place, too. Oooh! And a great Mex place! Can't remember the name. Rats!

Thanks, Geo, for mentioning it!