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Houston is experiencing its third ‘500-year’ flood in 3 years

washingtonpost.com

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Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#21

Post by mannykannot »

TallGuyShort wrote: post #7
bkohlmann wrote: post #2

While the article obliquely makes reference to this, I wonder if this is somewhat similar to the "birthday" problem in statistics. Any given person has ~1 in 365 chance of being born on a particular day. Yet, if you have 30 people in a room, there is a greater than 50 percent chance that at least one PAIR has the same birthday. Given the hundreds of cities (thousands?) in the US that may be affected by a flood, it's…

>> Of course, the "once in 500 years flood" may also be an inaccurate probability as well I suspect that's it. Of course I may be falling into the same birthday paradox here, but a similar thing happened when it flooded where I lived now. The x in "x-year Flood" kept increasing (I'm inclinced to blame that on sensationalizing news for ratings), but people kept comparing it to the 3 or 4 similar floods that happened i…

There is always considerable political pressure to low-ball the estimates. That is hinted at in this article, and it happened in New York, where the first post-Sandy flood zone maps provoked widespread opposition from those in the newly-expanded zones, and they were rapidly scaled back. There is, of course, some uncertainty in the estimation, but it seems likely that the official maps will be, at best, based on the most favorable possible interpretation of the data.

Mother nature does not respect grandfather clauses.

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#22

Post by sitkack »

jmcgough wrote: post #15
diafygi wrote: post #6

Howdy! I work in cleantech, and I guess it's that time again for a what-can-you-do-about-it post :) To start, here's my favorite climate change joke: "They say we won't act until it's too late... Luckily, it's too late!" ==So what can you do about it?== The biggest thing that is most relevant to the HN audience is that you can work at a new energy technology company! Our industries are out of the R&D stage and are cu…

The alternative approach to working directly towards solving the problem is to work at a mature tech company with higher pay, and donate 10% or more of your income every year to a non-profit like the Natural Resources Defense Council.

Work where your skills have the highest impact. Sometimes it translates into labor -> dollars.

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#23

Post by jdavis703 »

diafygi wrote: post #6

Howdy! I work in cleantech, and I guess it's that time again for a what-can-you-do-about-it post :) To start, here's my favorite climate change joke: "They say we won't act until it's too late... Luckily, it's too late!" ==So what can you do about it?== The biggest thing that is most relevant to the HN audience is that you can work at a new energy technology company! Our industries are out of the R&D stage and are cu…

Talking about Cleantech, if you live in California you can signup for Solar Choice from PG&E. It charges you extra for electricity, with the proceeds going to a program that offsets your electrical consumption by building new renewable energy sources. Here's a link to get started: https://www.pge.com/en_US/residential/solar-and-vehicles/opt....

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#24

Post by ncallaway »

walshemj wrote: post #20
bkohlmann wrote: post #2

While the article obliquely makes reference to this, I wonder if this is somewhat similar to the "birthday" problem in statistics. Any given person has ~1 in 365 chance of being born on a particular day. Yet, if you have 30 people in a room, there is a greater than 50 percent chance that at least one PAIR has the same birthday. Given the hundreds of cities (thousands?) in the US that may be affected by a flood, it's…

its the gamblers fallacy black 17 has not come up for ages so its more likely to come up - looks like the journalist does not understand probability

Except there's a very good ability to know precisely the odds of what the ball landing on black 17 are.

It's a very complicated question to determine what a 1/500 odds of flooding are.

So, it's very possible that this isn't the gambler's fallacy, but rather the model itself is inaccurate.

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#25

Post by mikeash »

walshemj wrote: post #20
bkohlmann wrote: post #2

While the article obliquely makes reference to this, I wonder if this is somewhat similar to the "birthday" problem in statistics. Any given person has ~1 in 365 chance of being born on a particular day. Yet, if you have 30 people in a room, there is a greater than 50 percent chance that at least one PAIR has the same birthday. Given the hundreds of cities (thousands?) in the US that may be affected by a flood, it's…

its the gamblers fallacy black 17 has not come up for ages so its more likely to come up - looks like the journalist does not understand probability

It's more analogous to getting black 17 six times in a row. It is possible, but it's weird enough to justify thinking that you've misunderstood the game, or the game has changed.

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#26

Post by mannykannot »

rlglwx wrote: post #12

Maybe we should change the nomenclature, 500-year flood denotes once every 500 years. As opposed to a 0.2% chance. This, in turn, causes people that don't pay attention to floodplain maps to say, "we had a 500 year storm last year, we are good for another 500 years". That, my friends, is a prime example of the gambler's fallacy.

There is also a feeling that a 100-year event is too rare to be concerned about, though I don't know that changing it to a 1% per annum would change many perceptions.

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#27

Post by polotics »

bkohlmann wrote: post #2

While the article obliquely makes reference to this, I wonder if this is somewhat similar to the "birthday" problem in statistics. Any given person has ~1 in 365 chance of being born on a particular day. Yet, if you have 30 people in a room, there is a greater than 50 percent chance that at least one PAIR has the same birthday. Given the hundreds of cities (thousands?) in the US that may be affected by a flood, it's…

No it's not the same thing. The 500 was a Houston stat, not a US overall one.

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#28

Post by WorldMaker »

idlewords wrote: post #13
rlglwx wrote: post #12

Maybe we should change the nomenclature, 500-year flood denotes once every 500 years. As opposed to a 0.2% chance. This, in turn, causes people that don't pay attention to floodplain maps to say, "we had a 500 year storm last year, we are good for another 500 years". That, my friends, is a prime example of the gambler's fallacy.

The nomenclature is not the problem, the problem is making numerical estimates of low probability events based on just 150 years of data and a raft of modeling assumptions.

The problem is not making numerical estimates of low probability events or how such events are modeled: it's completely ignoring the statistical probability distributions of the model. All of the models are extremely "long tail" distributions and just about entirely ignoring the long tail.

We shouldn't be referring to this as a low-probability flood but as a high sigma flood.

ETA: Disclaimer: Day job includes rainfall statistics analysis.

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#29

Post by SideburnsOfDoom »

bkohlmann wrote: post #2

While the article obliquely makes reference to this, I wonder if this is somewhat similar to the "birthday" problem in statistics. Any given person has ~1 in 365 chance of being born on a particular day. Yet, if you have 30 people in a room, there is a greater than 50 percent chance that at least one PAIR has the same birthday. Given the hundreds of cities (thousands?) in the US that may be affected by a flood, it's…

> Of course, the "once in 500 years flood" may also be an inaccurate probability as well

Or rather, the odds of that kind of flood increase a bit each year.

Re: Houston is experiencing its third ‘500-year’ flood in 3 years

#30

Post by twinkletwinkle »

ChadyWady wrote: post #9
bkohlmann wrote: post #2

While the article obliquely makes reference to this, I wonder if this is somewhat similar to the "birthday" problem in statistics. Any given person has ~1 in 365 chance of being born on a particular day. Yet, if you have 30 people in a room, there is a greater than 50 percent chance that at least one PAIR has the same birthday. Given the hundreds of cities (thousands?) in the US that may be affected by a flood, it's…

From what I understand of the article, the "1 in 500 years" measure is based on the estimated probability of a flood on a given year in a local area. So the probability of a "1 in 500 year" flood in Houston is independent of the probability of a "1 in 500 year" flood for another city.

Right what the parent comment is saying is that look at a map of the US, how many major cities are there. The odds of two "1 in 500 year" floods happening consecutively are low for any individual city. But if you have enough cities it will happen somewhere. And then you write the article about it.

It's kind of analogous to hitting a golf ball into an open field and then exclaiming "Of all the blades of grass, the ball landed on this one!" It's only interesting if it goes in the hole with the flag, otherwise you have a sort of selection bias going.

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