After the enormous storm event that was dubbed ‘the worst in 50 years’ to begin with, and ‘the most significant weather event we’ve ever had’ in the end, a large amount of damage was seen across South Australia after the low had passed. And whilst it certainly was a very big event, it is also a very big call to say it was the most significant ever, especially when you go back through the history books. Given the highly connective nature of the modern world and electricity/telecommunications being such an integral part of our lives, it is reasonable to say we are more vulnerable than ever to such storm events. Suggestions of stronger tornadoes, much bigger rain events and wilder winds have all been recorded in the past, but that isn’t to downplay this event, just a reminder that whilst events like this are certainly rare, they have happened before, and will happen again. But I will say this was up there with the best, a big part of which was due to its broad impact, and the particularly severe storms on the Wednesday.
A breakdown of some of the main events. This certainly isn’t to say this was all that happened, but these are events that stand out for me.
- 5 confirmed tornadoes, definitely more, potentially many more. I’d hedge my bets that we had a dozen touchdowns at least during the Wednesday simply due to many of these cells going unobserved. There is every possibility that this was one of the biggest tornado outbreak in Australia’s history. In South Australia we often see atmospheric shear profiles supportive of supercells and tornadoes given our latitude, our biggest issue is and always will be available moisture due to the huge dry continental air to our north, which is why we often see our best storms in the wettest years.
- Hail larger than tennisballs recorded in Blyth and apparently Snowtown, golf balls at Cleve, which caused huge crop losses. What makes this so significant, is it is RARE to see hail larger than golfballs in South Australia, even in November when we still have cold uppers and much higher instability potential. The fact that hail of this INCREDIBLE SIZE occurred in late September, with sub 20 degree temperatures is astounding. Snowtown obs prior to the supercell peaked out at 19.2/15.6. It is clear the relatively cold weather allowed a lower freezing level, combined with the strong upper divergence, high dewpoints and near dry adiabatic lapse rates for a short distance (in height) through the lower-mids, all contributed to this. And of course properly rotating updrafts to allow the recycling of downdrafts/updrafts in the storm. In all honestly, this stands out more for me than almost any other aspect of this system. About the maximum size you will ever see in South Australia.
- Widespread strong to gale force winds, locally storm force on coasts in association with the western flank of the low.
- A central pressure in the low of 972mb just south of the gulfs. Very very rare to have such a deep low, hence the severe weather.
- Widespread heavy rainfall in two lots, the first from the aforementioned thunderstorms on the Wednesday, and the majority on the Thursday from the low and its associated rainbands running ashore.
- Flooding associated with this rainfall. I’m not aware (yet) of any rivers reaching historical levels, however the broad scale of the flooding is quite rare. Most of the Mid North and the Adelaide Hills suffered some form of flooding with many rivers bursting their banks.
- A significant storm surge which severely damaged a number of jetties in South Australia, including long standing ones such as Port Germein, which has been in existence since 1879. The impact however has likely been increased as a result of sea level rises since its inception, as sea levels have risen 10-20cm in this time. Some locals quoted as saying the worst damage in 50 years.
Given the broad scope of the flooding, the statewide outages which lasted two days where I live and the telecommunication blackout which lasted over 5 days in Clare, I spent the entirety of the event around the Clare Valley, simply due to the dangers of leaving (and getting stuck), and who doesn’t want to be there when their own town floods! Doesn’t happen everyday.
The big part of why the flooding was so widespread, is simply due once again to the negative IOD influencing our weather this winter and spring, with some very much above average rainfall leading up to this event. Catchments were saturated, or near saturated throughout, and the reality is even falls of 30mm across catchments were sufficient to cause rivers to burst their banks. Here in the Clare Valley, we had 20-40mm from the storms on Wednesday, and a further 50-70mm on the Thursday. On top of the previous events in September, we ended up with a whopping 220mm in Clare itself, the biggest month of rainfall I have seen in all my years of watching weather. Whilst not directly comparable due to BoM closing the long running rain gauge at Clare post office (what a huge shame) in 1994, and Clare High School taking over (a much drier site), and the possibility of southern Clare being slightly wetter than the town centre, we still easily surpassed the all time September record going back to 1862. The old record was 197.2mm in 1972 (how’s the synchronicity there!). That is to say, we experienced the wettest September since European settlement in Clare.
The 6 month period leading up to this flood was exceptional, with outback South Australia receiving hugely unseasonable rainfall. Cloud band after cloud band extended down from NW Australia, it was an incredible wet phase we had entered.
Now for the year by year comparison for Clare, where I have cherry picked some of the wettest ever years, to see how they compare.
And historical rainfall.
As you can see, we are currently running level with many of these years, and therefore have potential to possibly exceed the all time yearly record.
Now for some pics, demonstrating just how much water was around! It’s hard to get a grasp of how deep some of these are, many streams went 1 metre over their banks. We ended up with 102mm in about 36 hours in my gauge in Clare.
Some videos to get an idea of the water motion. Some amazing turbulence in the bigger rivers.
Whilst floods like this may be considered bad from a human perspective, from an ecological perspective they are the boom times. Changing the habitats in rivers, washing away salinity (at first at least, rising water tables can bring higher salinity after wet years), creating new generations of river red gums, dumping fertile sediment across flood plains, improving water quality and one which often goes unnoticed, allowing native fish migration through the rivers. In South Australia, we actually have a few species which can migrate out to sea during these flood events, and up and down river channels to spawn and without the occasional flood event would have likely already have gone extinct.
I also remember a conversation, and talks about how Clare has been flood proofed from the amount of dams we have. Almost every last dam was full before this flood, and some were nearly destroyed by this flood. The reality is they provide next to no protection, and in many cases can often exacerbate events if one happens to give way. During dry times however, they are hugely detrimental to streamflow and consequently river health. A bit preachy, but this flood really did remind us how ineffective at flood mitigation during large flood events they really are.
Regardless of all this, I look forward to when streamflow returns to low flows, I can check out some of the bigger waterholes and see what life we have. It’s been an awesome wet season, which will likely soon come to an end. But for now it is as green as ever despite the 30 degree days nearing.