BTN: Seeding clouds to make rain and snow

NATHAN BAZLEY:

It's almost summer when Aussies tend to look up and hope for rain. But in some parts of the country scientists are taking a more proactive approach to the weather — to squeeze more rain out of the clouds. Sarah's been finding out how you can actually control some parts of the weather.

SARAH LARSEN, REPORTER:

Clouds. They can be a hopeful sign for farmers and winter holiday-makers, or they can really ruin your day. Wouldn't it be nice if you could make clouds do what you wanted? Believe it or not, scientists are already at work making clouds rain when and where they want. It's called cloud seeding.

ANDREW, CLOUD SEEDER:

It's quite good conditions.

SARAH LARSEN:

These guys fly into the clouds above Tasmania's hydro-electric dams and sprinkle a chemical which makes it rain. So how does it work? Well, you probably already know that clouds are made up of air and moisture. Water evaporates from the earth then cools to form tiny droplets and ice crystals which form clouds. If there's enough water up there, the droplets or crystals clump together and fall as rain. Cloud seeding speeds up the clumping process. Watch this demo.

ANDREW, CLOUD SEEDER:

It's just a freezer box we use as a cloud chamber.

SARAH LARSEN:

This is actually how cloud seeding was first discovered. 62 years ago, a scientist was making clouds by breathing into a freezer box just like these guys. To make it colder, he added some carbon dioxide or dry ice and to everyone's surprise tiny ice crystals started to appear. Those ice crystals attract more water then fall as rain. These days, cloud seeders usually use a chemical called silver iodide and they don't always scatter it from a plane. These cannons are aimed at the clouds above New South Wales's ski fields. They're controlled from the ground by cloud seeders who scope out the sky for suitable clouds.

LOREDANA WARREN, SNOWY HYDRO:

We monitor for temperature, wind direction, wind speed, we look at the crystal formation.

SARAH LARSEN:

The cannons shoot tiny particles of silver iodide into the clouds which travel up and start ice crystals growing. But instead of rain they fall as snow, which makes this cloud-seeding project unique. The tourists and resort managers here think it's great. Before the cannons started firing in 2004, snowfalls in some places were the lowest they'd been in 50 years. But last season was the best in four years. And when the white stuff melts, the snow becomes water which fills up the thirsty snowy river and the huge dams which make up the snowy hydro-electric scheme. Cloud seeding goes on all over the world. During the Olympics, China used cloud seeding to try and drain clouds before they arrived over the opening ceremony so rain couldn't spoil the party. But not everyone's a fan. Critics say that cloud seeding just speeds up rain or snow that would have happened anyway and wringing out these babies isn't cheap. There are also concerns that if you drain clouds here somewhere else will miss out on the rain they should have had. At the moment, this snowy cloud-seeding project is still in experimental stages. The scientists here will give it another six years before deciding whether or not the cannons will stay.