Auckland Weather 27/01/23 and Cyclone Gabrielle

Forums › Off topic › Auckland Weather 27/01/23 and Cyclone Gabrielle

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#3040537 22-Feb-2023 13:59

muppet:

The cause of it all is pretty obvious when you think about it: It was the massive f***ing cyclone last Monday Night/Tuesday morning.

Good thing it was a one-off and we can ignore all the flow-on effects, given it will definitely never happen again.

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#3040539 22-Feb-2023 14:03

GV27:

Good thing it was a one-off and we can ignore all the flow-on effects, given it will definitely never happen again.

He didn't say/infer it was a one off

I read today that the one there 2 years ago was 1 in 250, but the AKL flooding a few weeks back was also a 1 in 250, followed up by Gabrielle

neb

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#3040543 22-Feb-2023 14:14

tdgeek:
I read today that the one there 2 years ago was 1 in 250, but the AKL flooding a few weeks back was also a 1 in 250, followed up by Gabrielle

However, as I've pointed out before with 1-in-100 events, those figures are in desperate need of revision given the effects of climate change. We had four 1-in-100 events last year and two so far this year (in mid summer!), so 1-in-100 is more like 1-in-2 or even 1-in-1 here.

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#3040546 22-Feb-2023 14:20

neb:
tdgeek:

I read today that the one there 2 years ago was 1 in 250, but the AKL flooding a few weeks back was also a 1 in 250, followed up by Gabrielle

However, as I've pointed out before with 1-in-100 events, those figures are in desperate need of revision given the effects of climate change. We had four 1-in-100 events last year and two so far this year (in mid summer!), so 1-in-100 is more like 1-in-2 or even 1-in-1 here.

100%

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#3040569 22-Feb-2023 15:15

I don’t think that’s how probability works.

A 1 in 250 year event means, for any given location, there is a 0.4% chance of that event occurring in that year. It doesn’t mean, phew, we had that event so now we don’t have to worry about it for another 249 years.

Likewise 1 in 100 year means a 1% chance. Granted, ongoing drivers may raise the percentage but the only things that get to 100% are things like the Asian Monsoon and even that varies in severity. ie Bangladesh floods often, but not every year.

Once again, dumbing things down so it can be understood by politicians and journalists leads to misunderstanding.

“We’ve arranged a society based on science and technology, in which nobody understands anything about science technology. Carl Sagan 1996

Benoire

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#3040588 22-Feb-2023 16:03

I was going to mention something similar dingbatt as I work in the engineering industry and have water engineers working for me... its all about the percentage chance a storm could meet the criteria for that event in terms of mm/hr rain. Climage change related aspects will force us to reconsider what a 1% AEP storm is in terms of rainfall compared to TP108 values used in Auckland but the AEP value would be the same just a different outcome.

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neb

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#3040597 22-Feb-2023 16:42

Dingbatt:
Once again, dumbing things down so it can be understood by politicians and journalists leads to misunderstanding.

Yup. That's why I used "one in a hundred" which is a probability and not "we're good for the next 99 years". Unfortunately I think we've lost that particular battle and, like words like moron and retarded whose meaning was misunderstood and misused, we'll have to invent a new way to talk about it.

Edited to add: Having said that, what do you use and how do you talk about it if everyone only recognises 1 in 100 years to describe this?

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#3040725 23-Feb-2023 01:13

neb:
tdgeek:

I read today that the one there 2 years ago was 1 in 250, but the AKL flooding a few weeks back was also a 1 in 250, followed up by Gabrielle

However, as I've pointed out before with 1-in-100 events, those figures are in desperate need of revision given the effects of climate change. We had four 1-in-100 events last year and two so far this year (in mid summer!), so 1-in-100 is more like 1-in-2 or even 1-in-1 here.

There will almost always be more than one 1-in-100 event of each type occurring in every century.

Each event has identifiable or surmised causes and our experts attempt to predict the probability of future events based on some measured or inferred statistical distribution for each cause. But if the causes are different then we will have more than one 1-in-100 prediction.

Many events such as floods also have location specific predictions so it is no surprise that more than one major catchment in New Zealand can have 1-100 floods in the same year from different causes. That’s why it is not as simple as saying we’re getting too many floods because each flood, even in one specific locality, can have very different causes.

The biggest impact in the last year is definitely not climate change but the unpredicted - and probably unpredictable - volcanic eruption in Tonga. I’ve seen estimates of 20% or more water added to the atmosphere in our part of the world. This cooled Antarctica strengthening the Antarctic vortex and holding much of that additional atmospheric water south of Australia until it was heavily dumped in Victoria and NSW. AFAIK, such events, having very different causes, have little relevance to 1-in-100 events predicted from other causes.

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#3040727 23-Feb-2023 01:29

Dingbatt:
I don’t think that’s how probability works.

A 1 in 250 year event means, for any given location, there is a 0.4% chance of that event occurring in that year. It doesn’t mean, phew, we had that event so now we don’t have to worry about it for another 249 years.

Likewise 1 in 100 year means a 1% chance. Granted, ongoing drivers may raise the percentage but the only things that get to 100% are things like the Asian Monsoon and even that varies in severity. ie Bangladesh floods often, but not every year.

Once again, dumbing things down so it can be understood by politicians and journalists leads to misunderstanding.

The dice don’t have a memory. You have a 1 in 6 chance of rolling a 6 on each throw. On each subsequent throw you have a 1 in 6 chance again. It’s quite possible to get eight sixes in a row as the dice have no memory. It’s not likely but it’s possible.

A fundamental lack of understanding of maths isn’t confined to politicians or journalists. “Common sense” practitioners are usually the worst.

GV27

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#3040733 23-Feb-2023 06:35

tdgeek:

He didn't say/infer it was a one off

No but ignoring the huge amounts of slash and silt that people are now dealing with because the cyclone is the cause of the problem is kind of lopsided.

We can't do anything about the cyclone deciding to head our way. We can make sure when we do get one, it doesn't make things much worse than they already are.

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#3040856 23-Feb-2023 12:57

More fear from Stuff

https://www.stuff.co.nz/national/weather-news/131312848/chance-of-tropical-cyclone-developing-in-the-pacific-next-week-metservice-says

Although those across the ditch say:

In an update on Wednesday evening, the Australian Bureau of Meteorology said there were no tropical lows in the Coral Sea at the time.

The chance of a tropical cyclone developing in the Coral Sea was “very low” through to Monday, increasing to “low” next Tuesday and Wednesday.

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#3040863 23-Feb-2023 13:09

But there’s an orange rain warning for the areas hit. Just too horrible to think of more mud and water for those poor people.

RunningMan

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#3040869 23-Feb-2023 13:27

Zigg:

More fear from Stuff

https://www.stuff.co.nz/national/weather-news/131312848/chance-of-tropical-cyclone-developing-in-the-pacific-next-week-metservice-says

It's hardly fear. Whilst I wouldn't always rate the quality of Stuff's reporting, it's a reasonable summary of the media release from Metservice dated 22 Feb 5.21pm.

neb

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#3040875 23-Feb-2023 13:47

RunningMan:
It's hardly fear. Whilst I wouldn't always rate the quality of Stuff's reporting, it's a reasonable summary of the media release from Metservice dated 22 Feb 5.21pm.

The problem is the Metservice with their oxymoronic "chance of" reporting, you could replace "Coral Sea" on the report with "Sahara Desert" and it'd be just as accurate. There's a chance of a tropical cyclone in the Sahara Desert. Not a very big chance admittedly, but still a chance. So it's up to the media to invent their own interpretation of what it means.

ezbee

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#3040883 23-Feb-2023 14:27

How much is underfunded Metservice, or saving its best for highest paying customers,
not serving the public interest?

You would have to know who are the dominant commercial customers of Metservcie and if they limit the level of detail given to others.

Maybe its just underfunding, next to no-one paid to be on duty for long weekend.
Perhaps even the NZ employment relations standard of demanding your staff take holidays a one time of year so you don't have to juggle them through the year?

Anyone close to Metservice know?

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