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.
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.
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?