With beautiful sunny days forecast this weekend across Australia we begin to think that summer is well on its way. We all know that summer in Australia can mean storms, rain, and cyclones if you’re in the right (or wrong) part of the country. But what about floods and drought? What are we in for?
“Word on the street is there is going to be another La Nina…”
Despite what happened last year, La Nina isn’t a bad thing. We’ve previously spoken about La Nina and El Nino and how they effect the climate across Australia but what can we expect this season? Note: La Nina doesn’t mean flood and El Nino doesn’t mean drought, they just increase the chance of each. The Bureau of Meteorology (BOM) has recently announced what we can expect this summer and it doesn’t sound as bad as last year.
The BOM has told us there is a probability of La Nina (a positive Southern Oscillation Index (SOI) over Australia) but not on the EXTREME scale of last year–we’re looking at about an 8.9. According to the BOM, about 70 per cent of the time, the SOI lies between +10 and -10. So what was the SOI this time last year? A whopping great +24.7! In climate terms, that’s crazy!
“Is La Nina or El Nino the only thing that influences rainfall?”
La Nina and El Nino aren’t the only factors. Two other major factors that influence our spring and summer rain are the Indian Ocean and the waters surrounding northern Australia.
There is a pattern of sea surface temperatures in the Indian Ocean that is connected to central and southeast Australian rainfall. Climatologists call this pattern of ocean temperatures the ‘Indian Ocean Dipole‘, or ‘IOD’. When these temperatures are warm in the east and cool in the west, the IOD becomes negative and rainfall across Australia increases. Last year’s IOD was extremely low -1.0, a sure bet for heavy rain; whereas it is currently a much different +0.8, an indication the heavy stuff is not so likely.
Another factor is the ocean temperature off the North East coast of Australia. When the water is warm, there will be more evaporation and therefore more rainfall. 2010 brought the warmest ocean temperatures on record around Australia and rain to boot! This year, the oceans are still warm but not anywhere near last year’s record highs.
“So what does it all mean?”
According to the BOM, last year at this time:
- a raging La Niña;
- a ripping negative Indian Ocean Dipole; and
- record warm sea surface temperatures off our northern coast.
These three factors created a ‘perfect storm’ in terms of climate and rainfall, floods and cyclones but it will be different this year.
This year we have a neutral Pacific Ocean; a positive Indian Ocean Dipole; and average to slightly cool temperatures off our northern coasts. So that means:
- a less angry La Nina;
- almost the opposite in terms of Indian Ocean Dipole–so less rain; and
- only mild sea surface temperatures
For rainfall, that’s a very different mixture to last year. For more information, and the complete story, read the Bureau of Meteorology’s very own blog. It’s excellent!
Did floods or drought affect you in recent years? Where are you located? We like to know where you are from so we can write stories that relate to you!