One of the first columns I wrote for Eco-News was just as the 2018-2019 drought broke. I wrote: “I went out in my shorts to check my rain gauge, loving the caress of the raindrops running down my back.”
It was the first meaningful rain we’d had for months. I lost some mature trees in that drought and with the talk of a severe El Niño developing, I’m wondering if we are in for a repeat of that time. It seems timely to recap the influences of the El Niño and other influences on our climate.
The El Niño is one extreme of what meteorologists call the El Niño – Southern Oscillation (ENSO) Index which tracks the difference in ocean temperatures between the waters near Australia, and those near Peru.
During El Niño, sea surface temperatures near Peru are warmer, and those nearer Australia are cooler, and the ENSO index is negative. When these conditions are reversed, it’s known as La Niña, and the ENSO index is positive. It’s actually a lot more complex than this, and meteorologists now divide this area of ocean into different zones, as they have different influences on our climate, but broadly if the ENSO index is more than 7 out from its mean value, an El Niño or La Niña will be declared. El Niño conditions generally mean less rain for most of Australia. During the 2018-2019 drought the index was around -10. But during 2023-2024, which generally was not as bad a drought, it got down to -18. Recently it was at about -30, and has been described as “supersized” and a “one in a thousand years” event. However, it is on its way up again. So should we be very afraid?
Not so fast – there’s more to this. One of the most important influences is the Indian Ocean Dipole (IOD). Similar to the ENSO, it tracks differences in tropical Indian Ocean sea temperatures between the western (near Africa) and eastern (near the top of Australia). If it’s warmer near Africa, it’s positive, if warmer near Australia, it’s negative. A positive IOD will reinforce the effects of an El Niño. At the moment, it’s relatively neutral.
The Southern Annular Mode (SAM) measures where the westerly winds to the south of Australia are blowing. When they contract towards Antarctica, rain-bearing cold fronts don’t penetrate as far into southern Australia. When they blow further north, we get more rain. Again, right now they’re about normal, though they can change quickly.
The Bureau of Meteorology (BOM) considers all these factors (and more) in compiling its long-term forecasts, and they are for a hotter and drier spring than in the past, but mitigating towards the end of the year. At this stage, it seems we are in for a horror spring with high temperatures, low rainfall, and high bushfire danger.
The BOM has excellent resources on its website, including extensive information and graphs, it’s well worth a visit if the vagaries of our weather interest you.
