Could cloud seeding be used in the UK?

The process of artificially drawing rain from out of clouds is called cloud seeding, and has been prominent in the news, as the Chinese government announced an aggressive programme of artificial rainmaking to try to save their harvests after the country’s driest summer since records began in 1961. They do have form in this area, having fixed the weather for the Beijing Olympics back in 2008, but not on the scale they’re proposing now. Maarten Ambaum, from the University of Reading, has been speaking to Will Tingle, about how cloud seeding works, and if it could be feasibly used in the UK.

Maarten - Rainfall enhancement works by injecting salts, typically, into clouds. And what these salts do is they make ice crystals form. They act like cloud colonization nuclei, and those ice crystals. When they form, they can grow quite rapidly in the cloud. And the idea is then that those ice crystals might fall as precipitation. So these cloud seeding processes they have several purposes, so it's not just increasing rainfall or increasing snow, but people also try and use it to reduce damage by hail, so hail suppression. Of course, hail damage is a high economic costs so there's a lot riding on it if you could actually prevent hail from falling. So that's another typical application of of cloud seeding. It should be said that it's not very clear how efficient cloud seeding is. It's very hard to measure effects of cloud seeding. There's a lot of variability in nature, in the amount of precipitation that you might get out of any cloud, there's no typical cloud, all clouds are very different. They're very turbulent, they're very transient. And so it's very hard to measure in such systems whether any intervention will have an effect

Will - Which countries are currently using cloud seeding the most?

Maarten -目前我think most of the activity around cloud seeding is currently in the middle east, where there is a sustained effort by state actors to fund cloud seeding operations. So I'm involved with a big rainfall enhancement research program, which is funded by the United Arab Emirates. And so one of the things that our team at the university of Reading contributes to that research program is to examine to what extent, instead of using typical cloud seeding salts, you could use electric charge to make to make cloud droplets coagulate into bigger drops and produce rain that in that way. So instead of injecting salts, you really would be injecting electric charge. And our research program is seeing whether electric charge can help improve the efficiency of cloud seeding operations.

Will - So these salts that are involved in the rainfall enhancement process, are they in any way harmful to the environment?

Maarten - So the salts that are typically used are- dry ice, frozen CO2, silver iodide and normal table salt. And all of these substances have no environmental or health hazard that we are aware of at all. And at the same time the amount of salts that are being seeded into clouds during any operations is so small that, that it, it would have very little impact anyway but the soils themselves are not considered harmful at all.

Will - Cloud seeding is becoming more prominent in the public eye. Do you think that cloud seeding, as we know it right now, could ever exist at a scale so large that one country's cloud seeding could potentially steal water from any of its neighboring countries?

Maarten - So on a smaller scale, it's possible to steal water, if you want to call it like that, from rain falling on a farm next door, which doesn't fall on your farm. So at that level, it is conceivable to think of stealing water that is only an issue. If you really can target your cloud seed such that it will rain over one farm, but not the next farm. And that is actually in practice, not really the current state of affairs. Now on a larger scale like between countries, that's an irrelevance. It is not the case that if you make it rain over the United Arab Emirates, that that rain cannot fall over Saudi Arabia anymore, removing a cloud or several clouds via precipitation doesn't remove clouds from another area because clouds are transient, they reform and they remove themselves, et cetera. So on a larger scale, it's an irrelevance really to suggest things that one country can steal water from another country.

Will - And why would you say that cloud seeding isn't particularly feasible for the UK?

Maarten - As the word says, cloud seeding is a matter of there's a cloud and what you're trying to achieve with cloud seeding is to make the small cloud drops to change that into precipitation. So what needs to happen is you need to come up with some process that makes the small cloud drops into bigger cloud drops. However, in the United Kingdom, when there is drought, that is not due to the fact that there are clouds there that don't rain. When there's droughts in the United Kingdom, that's typically due to the fact that there are no clouds around. The weather systems tend to sort of evade the United Kingdom, they follow the jet stream typically. And the jet stream during drought periods is usually displaced. So those weather systems and the clouds that come with them don't come over the United Kingdom and when there is no clouds to seed, cloud seeding is nothing, it can achieve nothing. You can't seed clear air to produce rain.