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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

#91

Post by Spooky23 »

danmaz74 wrote: post #68
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…

How do you count "floods"? If there is one hurricane that causes floods in 3 cities, is that 1 flood, or 3? If it's 1 - which is what I think is meant when saying "a 1 in XXX years flood" - then your comparison doesn't hold, because the number of floods isn't dependent on the number of cities, but on the distribution of cities on the land, and specifically in flood-prone areas.

IMO you need to look at something other than city limits. Cities like Houston and LA are huge cities geographically. IMO you need to look at regional and per capita impacts.

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

#92

Post by dmurray »

bmm6o wrote: post #58
curiouscats wrote: post #11

Earlier quoted context omitted.

A 500 year flood event is very likely new data that tells us our prediction it was a 1 in 500 year event was wrong. http://engineering.curiouscatblog.net/2008/07/13/500-year-floods/ It is of course possible, it was actually a once in 500 year event. I just believe it is much more likely our previous conclusion was faulty. Our prediction of 500 year floods is not very good, we rely on way less than 500 years of data.…

This is part of the reason few private insurers offer flood insurance. They understand they there isn't enough information to properly price the risk. The historic data is spotty, we don't understand the geography well enough, you have to understand how construction and urbanization affects water absorption over long distances. If everyone who claimed to know what a 500-year storm looked like had to pay out every tim…

I don't understand this. Even if they can't assess the risk in any one property, can't they estimate the total amount of flood damage in (say) the US each year, and spread the risk across thousands or millions of properties?

If the answer to that is that only people in areas vulnerable to flooding would buy insurance, and the companies would have to pay out too much - well, that means the insurance buyers are pricing the risks better, and the insurance company should hire some of them.

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

#93

Post by dv_dt »

bmm6o wrote: post #58
curiouscats wrote: post #11

Earlier quoted context omitted.

A 500 year flood event is very likely new data that tells us our prediction it was a 1 in 500 year event was wrong. http://engineering.curiouscatblog.net/2008/07/13/500-year-floods/ It is of course possible, it was actually a once in 500 year event. I just believe it is much more likely our previous conclusion was faulty. Our prediction of 500 year floods is not very good, we rely on way less than 500 years of data.…

This is part of the reason few private insurers offer flood insurance. They understand they there isn't enough information to properly price the risk. The historic data is spotty, we don't understand the geography well enough, you have to understand how construction and urbanization affects water absorption over long distances. If everyone who claimed to know what a 500-year storm looked like had to pay out every tim…

To re-emphasise what the poster before you said - not only could the model be wrong, but even if it was right once before, you have to keep up the model against all the construction changes in the area that alter the watershed, as well as account for climate change contributions.

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

#94

Post by Mz »

bmm6o wrote: post #58
curiouscats wrote: post #11

Earlier quoted context omitted.

A 500 year flood event is very likely new data that tells us our prediction it was a 1 in 500 year event was wrong. http://engineering.curiouscatblog.net/2008/07/13/500-year-floods/ It is of course possible, it was actually a once in 500 year event. I just believe it is much more likely our previous conclusion was faulty. Our prediction of 500 year floods is not very good, we rely on way less than 500 years of data.…

This is part of the reason few private insurers offer flood insurance. They understand they there isn't enough information to properly price the risk. The historic data is spotty, we don't understand the geography well enough, you have to understand how construction and urbanization affects water absorption over long distances. If everyone who claimed to know what a 500-year storm looked like had to pay out every tim…

No, that isn't why. I worked in insurance. Not homeowners insurance, but I had a certificate and processed claims.

The reason is that most human settlements occur in flood plains because we cannot live without water. We drink it. We bath in it. We irrigate crops with it. Flood plains have fertile soil. We use rivers and oceans for essential cargo transit.

Insurance is about risk management. It is a form of betting. And there is no bet here because there is no question of if it will flood. The question is only when will it flood?

That's a fool's bet to say "I will pay you X amount of money if it floods" when it is guaranteed to flood sooner or later. That amounts to charity, not insurance.

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

#95

Post by MarkMc »

The problem is that the person who judges the probability at 1-in-500 doesn't have any skin in the game.

The judgement of the US meteorological office affects where people can build houses and how much they pay for government insurance. Homeowners have a strong financial interest in underestimating the probability of a severe flood, so there is likely subtle political pressure applied to the met office assessments.

For a more accurate assessment, the government should buy a sizeable insurance policy from several reinsurance companies and use it to calculate the implied probability.

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

#96

Post by sjg007 »

idlewords wrote: post #18
tertius wrote: post #16

Earlier quoted context omitted.

If we have a baseline of 500 year flood level at 0.2% and it's well over that then yes there is a basis for making this claim. I wouldn't make this claim though...

I don't think I understand what you're saying. To be able to say things about 0.2%/year events, we would need many thousands of years of data on an unchanging system.

This is not true. You can assume a uniform prior and run your model through bayes law and come up with an estimate.

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

#97

Post by schoen »

Mz wrote: post #94
bmm6o wrote: post #58

Earlier quoted context omitted.

This is part of the reason few private insurers offer flood insurance. They understand they there isn't enough information to properly price the risk. The historic data is spotty, we don't understand the geography well enough, you have to understand how construction and urbanization affects water absorption over long distances. If everyone who claimed to know what a 500-year storm looked like had to pay out every tim…

No, that isn't why. I worked in insurance. Not homeowners insurance, but I had a certificate and processed claims. The reason is that most human settlements occur in flood plains because we cannot live without water. We drink it. We bath in it. We irrigate crops with it. Flood plains have fertile soil. We use rivers and oceans for essential cargo transit. Insurance is about risk management. It is a form of betting. A…

I find this a little confusing, because one can also purchase life insurance, and mors certa, hora incerta.

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

#98

Post by euyyn »

Mz wrote: post #94
bmm6o wrote: post #58

Earlier quoted context omitted.

This is part of the reason few private insurers offer flood insurance. They understand they there isn't enough information to properly price the risk. The historic data is spotty, we don't understand the geography well enough, you have to understand how construction and urbanization affects water absorption over long distances. If everyone who claimed to know what a 500-year storm looked like had to pay out every tim…

No, that isn't why. I worked in insurance. Not homeowners insurance, but I had a certificate and processed claims. The reason is that most human settlements occur in flood plains because we cannot live without water. We drink it. We bath in it. We irrigate crops with it. Flood plains have fertile soil. We use rivers and oceans for essential cargo transit. Insurance is about risk management. It is a form of betting. A…

That reasoning fails in the face of there existing earthquake insurance in the Bay Area.

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

#100

Post by dlp211 »

pdq wrote: post #90
mbroncano wrote: post #77

The elephant in the room has been mentioned somewhere else these days: severe lack of planning and crumbling infrastructures. Remarkably how ne of the few non-partisan issues on the table goes under the radar time and time again. Tongue in cheek, we might think only polemic issue get the attention of the public. There is also the notion of national pride. We built our infrastructural base earlier than pretty much any…

Which other city in the US can handle 40 or 50 inches of rain, and 15 trillion gallons of water, within a one week timespan? That's as much rain as most US cities get in a year. This is not the fault of poor planning or poor infrastructure in Houston. It's freak weather event that shouldn't just be given partisan rhetoric.

Probably none, but it's not a matter of what city could survive unscathed, it's a matter of what city has minimized the consequences. Houston has allowed for basically unfettered growth constraining their bayou's and preventing flooding infrastructure to be built. Hopefully Houston uses this disaster to rezone and allow for appropriate land management.
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