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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

#111

Post by tertius »

ars wrote: post #85
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...

> If we have a baseline of 500 year flood level at 0.2% That's exactly the point. We don't have that baseline, despite acting as if we do. We would need data going back 5,000 years to do that.

You're right.

But he's going off of what is established, whether that is faulty or not.

So his claim is based on something faulty, but it is based on something.

Your qualm is not with him or his statements, rather with the standards for current 10 year/100 year/500 year estimates.

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

#112

Post by xbmcuser »

curiouscats wrote: post #11
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…

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.…

One of the things that is expected with global warming is heavier rain as the seas get warmer. This 500 year rain calculation is looking at the past for prediction but the future is different.

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

#113

Post by Taniwha »

empath75 wrote: post #46
waqf wrote: post #8

Earlier quoted context omitted.

Good point, but the chance of a given city having a 500-year flood in three given successive years is only (0.002)³ = 8 × 10⁻⁹. So even if we allowed for 100 U.S. cities, 10 different natural disasters and 10 different three-year periods we're still talking about a probability of less than 0.01%.

And it's not like Houston is the only city having 100 year+ floods regularly.

yes, it's almost as if the climate is changing

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

#114

Post by mirimir »

> Climatologists say the mechanism by which this is happening is fairly straightforward. “Warmer air can contain more water vapor than cooler air,” according to the 2014 Climate Assessment produced by the U.S. government. “Global analyses show that the amount of water vapor in the atmosphere has in fact increased due to human-caused warming. This extra moisture is available to storm systems, resulting in heavier rainfalls.”

This is just so totally obvious. But I've rarely seen anything in news coverage about increased mean atmospheric water concentration. Also, increased water content is (of course) the expected multiplier for increasing CO2.

Edit: spelling

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

#115

Post by Retric »

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's not the problem. Private insurance does not offer flood insurance because A) it tends to all be due at the same time requiring a very large fund. B) It also promotes people living in flood prone areas. C) It's very hard to asses risks. Combined and you end up with bankrupt insurance companies.

The industry also feels B makes selling flood insurance a bad idea. That said, there are Private policies you can buy in some areas.

PS: Insurance companies like frequent small scale random events like car accidents, because they are easy to plan for.

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

#116

Post by maxerickson »

imnotlost wrote: post #72
rsync wrote: post #37

Earlier quoted context omitted.

"Fort Bend County Judge Robert Hebert stated that Hurricane Harvey is more like a 800-year event" 500 years, 800 years ... even 1000 years - none of those are timetables that planning for city ^H^H^H^H region the size of Houston should be operating on. A city that large, that populous and with that much economic activity that is crucial to the world should be using risk models to 10k year events. This is not unpreced…

Which American city, if any, plans for anything close to that time scale? Seems like every city, county, state, etc. screw up planning on less than human time scales - pensions and infrastructure maintenance for instance.

It isn't planning for a time scale though, it is a level of immediate risk mitigation.

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

#117

Post by Retric »

Mz wrote: post #105
euyyn wrote: post #98

Earlier quoted context omitted.

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

Major earthquakes are less frequent than major flooding. If the time frame is large enough and the timing uncertain enough, it can still make sense as a bet.

Frequency only changes premiums, car insurance is much more likely to pay out than earthquake insurance per year. That just means it costs more money per year relative to the payout.

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

#118

Post by aaron695 »

danielvf wrote: post #3

Cue discussion on the works of Tabeb, and what a horrible job humans do at predicting the frequency of rare events.

Humans also predict un-rare events badly.

ie The time it takes to complete a work project.

Tabeb states the obvious, almost tautologies, without solutions, behind the wall of philosophy. Pointless stuff.

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

#119

Post by sdenton4 »

enraged_camel wrote: post #54
autokad wrote: post #19

Earlier quoted context omitted.

more likely their model is wrong. it reminds me of fukushima: https://ml.berkeley.edu/blog/2017/07/13/tutorial-4/

Their model is wrong, but it's because it assumes climate is stationary. Climatologists are actively debating what the models should look like when global warming is taken into account: https://i.imgur.com/HLxUBim.png edit: not sure why I'm being downvoted. I can only assume the downvotes are political in nature, which is a shame.

A screen cap of a discussion forum is a poor reference indeed...

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

#120

Post by ComradeTaco »

pixl97 wrote: post #33
TallGuyShort wrote: post #7

Earlier quoted context omitted.

>> 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…

>. It would seem the probably has gone up due to climate change That probably has a small reason to do with the increase, but your next line highlights the issue. > or that we're noticing the floods more now because there's more damage to be caused to more things that have been built up No, not exactly. The more stuff you build, the faster water runs off. Unincorporated land has a pretty high water slowing capability…

An additional on flooding:

When Rainfall * Area >= SoilAbsorption(See note) + WetlandAbsorption + ArtificialDrainage the end result is flooding.

Essentially the left hand side of the inequality has been slightly increasing because of climate change, but we're chipping away constantly at the right side of the equation in three ways.

(1) More and more soils in American metro areas have been covered by impervious surfaces for development. (2) More wetlands are being destroyed for development. (3) Artificial drainage is being under-built. Drainage is generally built for 1 in 100 year events but the rate of urbanization is increasing the magnitude of flooding. (Drainage is only a problem for the developer that hasn't sold what they're building.)

Note: Soil has a finite capacity for water infiltration.

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