At the beginning last week, Sydney was in the path of a pretty nasty storm. As you can see from the image above it measured roughly 300km across, and went on to dump over 400mm of rain across the Sydney area.
Using the weather information I was able to create the following plot, which shows how much rain fell during the event, and also shows that it fell pretty continuously (the plotted lines are mostly straight). However, what the graph can’t show is how frequently a storm like this might be expected to occur (the ARI). For that, the raw data needs a bit more processing.
I made sure I grabbed the weather data for Observatory Hill just after things started drying up on Wednesday, which ensured that I had rainfall information covering the whole event. A bit of Numbers processing allowed me to calculate the equivalent mm/hr rainfall for comparison against the Bureau of Meteorology IFD standard tables for set time intervals. The final result is the Annual Recurrence Interval.
|Max Rain (mm)||12.2||21.2||25.4||30.2||51.6||70.8||123.8||228.4||263.6|
The 30 minute recording interval of the data doesn’t unfortunately allow assessment of the short, typically high intensity periods, but for the available records it’s clear that this storm was only a 5-10 year rainfall event1.
Climate change is likely to bring events like this frequently (perhaps on average 2-5 years) with larger storms coming much more often. The last few years have seen Sydney experience weather much more like that of subtropical Queensland as opposed to temperate New South Wales.
The wind that accompanied the storm was pretty strong, with lots of power outages and tree falls in the region. Just after the main event I was out in Darling Point and happened upon this unfortunate vehicle.
- For the Observatory Hill location, other areas such as Maitland were hit much harder.↑