Rapidly flowing river

Meet our climate drivers

14 November 2018

We are Australia’s largest producer of clean, renewable energy, which we generate mostly through hydropower. This makes water really valuable to us and we like to make sure we have plenty of it in our lakes. But it means we are at the mercy of our climate and we really like to know when and how much it’s going to rain. 

While the weather can change a lot from day to day its general trend is driven by the climate and here in Tasmania there are three major climate drivers who love to crash the party and keep us on our toes. By keeping track of the movements of these three characters we can get a long term view of what the weather will be like months or even years in advance. 

If you haven’t met these three climate drivers let us introduce them to you.

El Nino - Southern Oscillation

El Nino is world famous (you could even say infamous). He appears when the Southern Oscillation Index (SOI) is positive for a sustained period and his appearance generally means it’s going to be hot and dry on Australia’s east coast while in South America it's going to be cold and wet.

Map of Australia and surrounding oceans with climate graphicsIn a normal year, when the SOI is neutral, trade winds blow from east to west pushing moist air towards Australia which makes it rain in many parts of the country. When the index goes negative for a while El Nino’s little sister La Nina comes out to play pushing more of that moist tropical air towards Australia and making it rain a lot. 

But when El Nino is in town the trade winds drive that moist air away from Australia towards South America. This can result in droughts and heatwaves across the country’s east coast.

The Weather Bureau says there’s a 70 per cent chance of El Nino making an appearance on Australia’s East coast this year. But while he’s expected to run amok on Tasmania’s east he doesn’t like to make the road trip across the state to the west coast, where most of our dams and lakes are.

While we’re always on high alert when El Nino is in the neighbourhood he leaves our rainfall alone. He’s the climate driver with the least direct impact on the water that runs into our dams and lakes.

Fun fact: Directly translated from Spanish El Nino means “the little boy”, although, for a little boy, he packs quite a punch.

Southern Annular Mode (SAM)

The next climate driver we’d like you to meet is SAM. She is not as famous as El Nino but has far more pull around our neighbourhood. 

She’s also pretty complicated. SAM likes to bring cold fronts up from the Southern Ocean which can cause a lot of rain when they get here. Sometimes she likes to go further away from the South Pole bringing rainfall to Tasmania and southern parts of Australia but other times she prefers to say close to home. That’s when the rain tends to dry up. 

When SAM is positive in the winter she can have quite a negative effect on the water that reaches our dams. When she’s negative in winter it’s going to get wet. 

But just when you thought you had her figured out, she changes. If she’s positive in summer most of Tasmania gets more rain except the southwest where she likes to keep it dry. On the other hand if she’s negative during summer most of the state will be dry except the southwest where she dumps more rain than average. 

This intricate climate driver has the biggest impact on our spring inflows. 

Indian Ocean Dipole (IOD)

And finally we have the cosmopolitan driver we like to call Indy. He’s a lot like El Nino except his stomping ground is the Indian Ocean. 

But unlike El Nino he’s quite fond of Tasmania’s west coast. In fact he’s making a visit right now.

Indy likes to bring moisture from the warm north east Indian Ocean across to south eastern Australia, including Tasmania. That moist air can deliver lots of rain. But if the north east Indian Ocean is cooler than normal the air won’t be as moist and we won’t get as much rain. This means Indy is positive. 

If Indy is positive during winter or spring he usually dries up the rainfall around the state and he makes it hot. That’s what he’s up to right now. As a result of Indy’s influence we have seen inflows reduced slightly. Luckily it’s coming off the back of a wetter than average winter, but more on that later.

The weather bureau says Indy plans to move on by the end of November (2018) because he’s not a fan of this side of the ocean during the monsoon (towards the end of spring).

Are we ready to deal with these gate crashers?

The short answer is yes. We’ve had a really wet winter / spring period and the state’s dams are looking good. Even if these guys are not around, the dam levels usually fall during summer and autumn because it’s drier then so we are prepared for that.

Our hydro dams peaked at just under 50 per cent this year which is a really secure position. Even with Indy crashing on the couch until the end of the month it’s not going to make much of a dent in our secure storage levels.

If El Nino turns up, as expected, he will stick to the north east and the east coast which will cause a bit of a headache for farmers and primary producers in those regions but won’t venture into our backyard in any meaningful way. 

Our team of experts manage our water supplies with seasonal fluctuation in mind to make sure Tasmania gets the most out of the water we have in storage. Couple that with top level climate forecasting from the Bureau of Meteorology and we are well prepared to deal with any climate driver that may turn up uninvited. 



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