Can California Make It Rain With Drones?

Faced with extreme drought, California continues its experiment with weather modification.

National Journal
Add to Briefcase
Brian Resnick
Oct. 7, 2014, 7:46 a.m.

Bil­lowy and filled with life-sus­tain­ing wa­ter va­por, the cloud passes over­head without emit­ting a drop of rain. In times of severe drought, that cloud is a frus­trat­ing, lum­ber­ing tease. That cloud is tan­tal­iz­ing. De­li­cious even. 

What that cloud needs is a kick start, a cata­lyst to squeeze the wa­ter out of it. It’s not sci­ence fic­tion; it’s called cloud-seed­ing. And in bey­ond-parched Cali­for­nia, it may be­come a vi­able op­tion to com­bat long-term wa­ter short­ages.

Cloud-seed­ers can’t make rain ap­pear out of clear blue sky. Rather, they cre­ate snow (and some­times rain) where it’s most likely to oc­cur—in clouds. Yes, that cloud is full of wa­ter va­por, but some­times, wa­ter needs to be coaxed in­to form­ing the ice crys­tals needed for snow (you can see this hap­pen­ing in this video). The seed­ing devices, which are mainly on the ground, burn sil­ver iod­ide in­to a fine mist that gets tossed up in­to the air. Sil­ver iod­ide is an in­ert chem­ic­al, mean­ing it won’t re­act chem­ic­ally with much in the en­vir­on­ment, but its struc­tur­al shape is per­fect for seed­ing ice crys­tals. Wa­ter va­por will col­lect around the sil­ver iod­ide and freeze in­to crys­tals, then those crys­tals will pre­cip­it­ate as snow. The snow fills moun­tain­sides, an, come spring, the snow melts and in­creases the fresh wa­ter sup­ply.

The Desert Re­search In­sti­tute op­er­ates sev­er­al such cloud-seed­ers in Cali­for­nia and has found that the pro­cess in­creases the pre­cip­it­a­tion out­put of a cloud by around 10 per­cent—though there is a lot of vari­ab­il­ity, cloud to cloud, and the ef­fect­ive­ness of the pro­cess has been de­bated. In 2003, a Na­tion­al Re­search Coun­cil study found little evid­ence in fa­vor of cloud-seed­ing, but mostly be­cause there wer­en’t enough data. “This does not chal­lenge the sci­entif­ic basis of cloud-seed­ing con­cepts,” the Na­tion­al Re­search Coun­cil as­sured in its con­clu­sion, call­ing for more re­search. “The sci­entif­ic com­munity now has the op­por­tun­ity, chal­lenge, and re­spons­ib­il­ity to as­sess the po­ten­tial ef­fic­acy and value of in­ten­tion­al weath­er-modi­fic­a­tion tech­no­lo­gies,” the coun­cil wrote. A study out of Wyom­ing is ex­pec­ted to be pub­lished in Decem­ber to more pre­cisely de­term­ine the be­ne­fit of cloud-seed­ing.

The Cali­for­nia cloud-seed­ers are stra­tegic­ally placed in its north­ern moun­tain­ous re­gion, where snowpack is an es­sen­tial com­pon­ent of the yearly wa­ter sup­ply. In the past year, the snowpack was de­pleted to one of its low­est re­cor­ded levels. As can be seen in the chart be­low, much of Cali­for­nia’s wa­ter comes from the snow-laden areas in the north­ern part of the state.

+ (U.S. De­part­ment of the In­teri­or, Bur­eau of Re­clam­a­tion)

Not only has the state’s snowpack di­min­ished, the on­go­ing drought in Cali­for­nia has got­ten so bad that the state is los­ing mass, as NASA has ob­served from space. That has wide-reach­ing im­plic­a­tions for a state with a massive ag­ri­cul­tur­al eco­nomy. “The wa­ter short­age could res­ult in dir­ect and in­dir­ect ag­ri­cul­tur­al losses of at least $2.2 bil­lion and lead to the loss of more than 17,000 sea­son­al and part-time jobs in 2014 alone,” re­ports the Na­tion­al Sci­ence Found­a­tion. By 2030, Cali­for­nia is pro­jec­ted to have a wa­ter sup­ply-to-de­mand de­fi­cit of 1.6 tril­lion gal­lons a year, the U.S. In­teri­or De­part­ment has pre­dicted.

“Even cur­rently, the sup­ply and de­mand are some­what out of bal­ance,” Shawn Blosser, an eco­nom­ic con­sult­ant with the Blue Sky Group, a pub­lic policy con­sultancy, tells me. “There really is no single sil­ver bul­let that is go­ing to solve the prob­lem.

Part of the solu­tion is com­bat­ing the rising de­mand for wa­ter (Blosser, work­ing with the Cali­for­nia think tank Next 10 has de­veloped a menu of policy ideas to re­duce de­mand—the an­swers aren’t easy, or cheap.) But part of the solu­tion is also to in­crease sup­ply, by cloud-seed­ing or per­haps a more scal­able meas­ure such as waste-wa­ter re­cyc­ling. In all, Blosser and Next 10 pro­ject that an in­creased ef­fort to seed clouds could re­duce the loom­ing wa­ter gap by 26 bil­lion gal­lons in 2030, at a cost of $22 per acre-foot of wa­ter (325,851 gal­lons). That’s markedly cheap­er than oth­er tech­no­lo­gies to in­crease wa­ter sup­ply. Wa­ter de­sal­in­a­tion, for in­stance, would cost $1,890 per acre-foot of wa­ter pro­duced.

But seed­ers aren’t a defin­it­ive an­swer to Cali­for­nia’s wa­ter prob­lems. Be­cause they’re ground based, if clouds aren’t over the seed­ers to be­gin with, we’re out of luck. Plane-based seed­ers ex­ist, but pi­lots can’t al­ways fly safely in­to cloud areas with the highest seed­ing po­ten­tial.

Enter the cloud-seed­ing drone. The DRI is cur­rently test­ing plans for a cloud-seed­ing drone pro­gram, with the goal of de­liv­er­ing the most ef­fect­ive dose of sil­ver iod­ide to the clouds with the greatest pre­cip­it­a­tion po­ten­tial, wherever they may be.

It may sound like a stretch, but it’s im­port­ant to keep in­nov­at­ing in wa­ter re­source man­age­ment. Even if Cali­for­nia’s drought eases in the next year, Blosser ex­plained, the long-term trend of wa­ter de­mand out­pa­cing sup­ply will con­tin­ue.

“There has to be a co­ordin­ated ef­fort on a lot of fronts to both lessen de­mand and in­crease sup­ply, to get the de­mand and sup­ply back in­to bal­ance,” Blosser said.