The Indian Ocean Dipole and Eastern Australian Droughts

Peter Hannam in The culprit behind east Australia's big dry explains that the Indian Ocean Dipole has a a huge effect on rainfall levels in Australia's eastern states.

In its so-called positive phase, tropical waters off Australia's north-west are relatively cool - compared with those near Africa - strengthening easterly winds and reducing the potential convection that typically supplies much of south-eastern Australia's critical winter and spring rains. A negative IOD has the opposite effect.

And of course, climate change is making it worse:

Dr Cai says that while the Indian Ocean is warming - along with others around the world - “the west is warming faster”. Under such conditions, "it’s easier to have an extreme positive IOD event", he said.
Such a future would be bad news for farmers, and raise doubts about the effectiveness of policies proclaimed to be "drought-proofing".
“We change the average climate by having these events more frequently or more strongly," Abram says. "It has an effect of changing our average rainfall.”

...

"We are perturbing the atmosphere in a profound way with greenhouse gases," England says. "How this changes our modes of variability is uncertain.”