Can we make it rain?

With the current drought occurring in parts of Eastern Australia, is there a better time to ask the question: can we make it rain? If you believe everything you hear then Minister for Agriculture and Water Resources has already told us, somewhat definitively, that we cannot make it rain. But is this, like many other things politicians say, fake news? It’s best to start with the basics.

How does rain form?

For a rain droplet to form on its own, the relative humidity (RH) at 5°C would have to be over 300%. So basically, in normal temperatures for the upper troposphere, it would have to be three times wetter than saturated for rain droplets to form.

Instead, they are formed on aerosols known as cloud condensation nuclei (CCN). This way the RH doesn’t have to be so high, because rather than collide with each other, they all just have to stick onto a CCN.

When the droplet grows large enough, it falls out of the sky. Yes, clouds contain liquid and frozen water that floats in the sky – I still can’t really wrap my head around that one.

Image credit: Author

 

Great, so let’s introduce some CCN and make it rain?

Not so easy. We’ve been trying that in a process known as cloud seeding, where a chemical such as silver iodide is released into the atmosphere as CCN. Let’s just say there have been some mixed results. You see, it depends largely on the weather conditions of the day. Is the temperature just right? Is there enough moisture in the air? Are the clouds of the right type? Is the wind blowing too strongly?

It can go wrong too. There was a recent incident in Tasmania where they chose to attempt cloud seeding inside a weather system that went on to flood parts of the island. Let’s just say, the Tasmanian cloud seeding program is still suspended. Even if they didn’t have any impact on rainfall, it isn’t a good look!

It’s all good news in the Snowy Mountains though, I promise. By introducing silver iodide into the atmosphere, researchers have been able to increase snowfall over the ski fields and raise dam levels.  There have also been some successful efforts in the USA, among many other locations. But these mostly occur when the clouds flow over mountains; again with the really precise conditions!

Can we make it rain over our drought affected areas?

Well, depends where the drought is really. If it’s near the Snowy Mountains then you’re in luck because we can. But it’s not quite like turning on a light switch, we don’t really choose when we can cloud seed. You kind of just go with the flow.

Why shouldn’t we make it rain?

Think of a cloud full of rain as a hot air balloon that is travelling through the sky. Let’s say this balloon drifts over drought affected NSW, so the state government decides they are going to release some silver iodide into the air and make the balloon fall over NSW.

Image credit: Sebastien Gabriel via unsplash.

Now lets say this balloon was originally headed towards New Zealand. If it reached New Zealand, it would have naturally fallen on the dry pastures of the North Island. This would have relieved some needy farmers there too. But we took that balloon before it could reach them.

Is it fair that we took the balloon of water that was destined to reach New Zealand? You could imagine that they wouldn’t be very happy with us.

Let’s also look at the big picture here. We’re in this mess of a rapidly changing climate that produces more frequent, prolonged drought, because of our history of releasing things into the atmosphere. Our best idea to solve this problem is to release more things into the atmosphere. If Darwin is right, I struggle to see how fit we really are for survival, if this is a technique we choose to employ.

So, can we make it rain? Well, technically the answer is yes. But the bigger questions is; do we really want to? I know my answer, what’s yours?


10 Responses to “Can we make it rain?”

  1. Jason Hobson says:

    Very interesting topic indeed! I was actually quite surprised to learn about the number of geoengineering programs that are already running, not just in Australia, but around the world. I assumed that if there was any issue for public debate, it would be the use of geoengineering and not the science behind our changing climate!

  2. randersen says:

    Very cool topic! like all geoengineering techniques, it seems like such a surreal and futuristic option. A larger issue with climate forcing is the potential to redirect the focus and funding away from GHG reduction measures.

  3. Jason Hobson says:

    Thanks for your comment! The case in Tasmania is confusing as a whole. The program was suspended because damaging floods occurred after they seeded, it didn’t really matter whether the seeding worked or not. There was no clear-cut answer to whether the seeding contributed to flooding, it’s hard to measure. In the media it looked bad that floods occurred after seeding technology was tested, so based on protecting their image, they suspended the program.

  4. codya says:

    Always woundered if this was possible, pretty cool! In the Tasmania trial you mentioned, did the seeding have any affect at all (i was a little confused by your wording)?

  5. Jason Hobson says:

    Thanks Tyler! Some of the research said that the concentrations of silver iodide are extremely low and were therefore nothing to worry about, but given that cloud seeding isn’t always successful I don’t like the idea! There are other methods that include using dry ice, but they are even less successful.

  6. Tyler Sudholz says:

    Very informative! I especially liked the balloon analogy.
    Is there much info on what happens to the silver iodide after it’s been released? Is it possible that after it’s fallen to the ground it pollutes or contaminates the land environment?

  7. Jason Hobson says:

    There definitely are legitimate reasons to have reservations! I like your way of thinking, there are some technologies that aim to increase the ability of soils to retain larger amounts of water. I think that this would be a great avenue for further research.

  8. Xiaohan Hu says:

    I really like your blog topic, I personally choose not to affect the weather because I believe it will result in too many political issues and the technology itself is also quite hard to control. I think the real solution here is to try to manage the water resource better and find a way to help the drought area to overcome the hard time.

  9. Jason Hobson says:

    Thanks!

  10. Gabrielle Stinear says:

    Super interesting article Jason! Very thought provoking