But how strong is this relationship? I’m using regional climate models to try to find out exactly how much our warm coastal waters matter to ECLs, which was just published in the Journal of Geophysical Research.
To try to answer this, I did lots of runs of a regional climate model over Australia during the years 2007-2008, changing sea surface temperatures to remove or strengthen the East Australian Current. Unsurprisingly, with cooler sea surface temperatures, we get fewer ECLs, and warmer oceans mean more ECLs. The change is about 20%, for a change in ocean temperatures of just 1-2°C.
The interesting thing is that this seems to mostly affect the weak systems – with warmer oceans, it’s easier for an East Coast Low to develop, even when the conditions in the atmosphere aren’t as favourable. The upper atmosphere is really important for the big ECLs, which still happen even with cooler SSTs, although warmer SSTs do help ECLs grow a little bit more intense.
Sea surface temperatures in the Tasman Sea in Australia are warming faster than most other places in the world. And while we know that cyclones are shifting south and the conditions favouring ECLs are likely to decrease, there’s a lot more uncertainty right near the coast.
Since most of us live near the coast, and ECLs are really important for things like dam levels, it’s important to know what will happen to the ECLs that matter most. And if ocean temperatures are important, we might see different changes in the future, which we need to plan for.
This work is a start, since nobody’s really looked at this question since 1992. But there’s still a lot to know about how, for instance, the temperature changes projected by climate models will do to ECLs, or if these results hold true in more complex global/coupled models. We also want to know more about individual events – for instance, were the record warm sea surface temperatures this year important for the record-breaking rain from the ECL in June?
That's one of the fun parts of being a scientist – there’s always more to learn.