The Indian Ocean Dipole is at a record high value. To quote Dr Suess’s Sleep Book: “This may not seem very important, I know. But it is, so I’m bothering telling you so.”
The IOD is an indicator of the distribution of surface temperature in the Indian Ocean. When it’s positive, like now, warm water is pushed up against Africa, and cooler water is found near Australia. This is like a smaller version of El Nino, where warm water is squished up against South America and cooler surface waters are found near Australia.
Earlier in my chequered career I was an ocean physicist, and one of the places I studied was the Indian Ocean near Australia, so this is a topic dear to my heart. And here’s what happens: warm surface water causes convection in the atmosphere above it, bringing heat and moisture up into the atmosphere, where the moisture condenses as rain. Over cooler ocean surface temps, not so much. Since weather patterns move from west to east (both hemispheres) convection over the Indian Ocean has major implications for Australia’s rainfall, particularly my part of Australia. The effect of the IOD on rainfall in Tasmania is much more pronounced than the effect of El Nino. Positive IOD means low rainfall.
Looking across the valley toward the village of Jericho. Except in the foreground, there is very little stock feed in this picture.
Over the last 12 months we’ve received less than half our annual average 600mm (24 inches) of rain. The last time it was this dry was back in 2006-2009. That three-year extended dry precipitated (no pun intended) me into a completely different management of my sheep. At the time, researchers were developing an awareness of the importance of the IOD on Australian rainfall, but the federal Bureau of Meteorology had not yet incorporated their research into operational forecasts. In 2008-09, there was actually a La Nina event, which should have been dumping rain on us, but as I said at the time: “If it’s La Nina, why are my gum boots still dusty?”
Today the Bureau of Met is much more switched on to the IOD, and we know a lot more about the way it behaves. Happily, it should start to break up and become neutral around Christmas, so with any luck we’ll get some late summer or autumn rain.
Defying the dry weather, this 5-year-old dogwood is blooming with gusto. It’s in a tree reserve area just behind me in the photo above.
Meanwhile, we’re doing ok for forage, but shepherding just got pushed up in priority, as I work to keep the sheep healthy and well fed by taking them to the various corners they don’t tend to go to on their own. Those corners tend to have the best biodiversity as well as overall better forage at the moment.
If you want to know more about my shepherding strategy for the next few months, check out my other farm journal—Come Shepherding.