
Houston is experiencing its third ‘500-year’ flood in 3 years - Mz
https://www.washingtonpost.com/news/wonk/wp/2017/08/29/houston-is-experiencing-its-third-500-year-flood-in-3-years-how-is-that-possible/?utm_term=.1ffa35d284d3
======
bkohlmann
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 actually quite likely that at least one
of them could have a pretty high probability of experiencing one in 500 chance
of something each year. I haven't run the numbers, of course, but we're
looking at Houston in isolation - it needs to be seen in the broader context
of all possible cities. We're focusing on the individual probability of
Houston having this improbable string of events, rather than looking at
Houston only being the city that experienced this phenomenon.

Of course, the "once in 500 years flood" may also be an inaccurate probability
as well, but if its not, then I'm not surprised this is happening SOMEWHERE.

~~~
curiouscats
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. Also in most places where this happens the massive changes to
the environment (roads, cities, paved over wetlands, constrained rivers...)
are not factored in well at all. Add to that global climate change and 500
year flood estimates are likely still poor today. The birthday problem doesn't
relate to us getting new data that changes what we used to know. A 500 year
flood probably is new data (that gives us a strong indication our previous
belief was wrong).

~~~
bmm6o
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 time one happened, we might have better
models.

~~~
Mz
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.

~~~
schoen
I find this a little confusing, because one can also purchase life insurance,
and _mors certa, hora incerta_.

~~~
Mz
A lot of life insurance is term insurance. So the bet is "will you die during
the years that your policy is in force?" Whole life is much, much more
expensive.

~~~
schoen
Could you then have the same kind of structures for flood insurance policies?
I had to pay every year to renew my renter's insurance policy, it only covered
losses during the course of that year, and the insurance carrier had
discretion to adjust the premiums or not to renew it.

~~~
Mz
In the US, flood insurance is provided by the government. And the premiums
still jump insanely sometimes.

It gets handled this way for the same reason our government provides welfare
et al: it makes no sense as a business, but the cost to the nation to do
nothing is a bigger problem.

~~~
cmurf
There is some private flood insurance these days, but I don't know who offers
it, in what locations, what the premiums are, and what kinds of exclusions
there are. Since it's a new thing, I think the claim that it'll be vastly
better than NFIP is invisible hand waving. Nevertheless...
[http://www.insurancejournal.com/magazines/features/2017/07/1...](http://www.insurancejournal.com/magazines/features/2017/07/10/456390.htm)

I think the bigger issue is that there is an inherent incompatibility between
free markets (or strict laissez faire, non-intervention of any kind) and
democracy. Of course people, in the millions, are going to say "help us" and
direct it at their various layers of government, and punish those who don't at
the election booth.

Therefore it stands to reason in major floods like this, that everyone is
going to get some kind of relief even if they didn't have flood insurance.
What I'm not sure of is whether the insured get 100% payouts and those not
insured get partial payouts? What's the incentive to have flood insurance,
except in smaller, localized, 50 or 100 year floods?

This is asset destruction and the only way to properly handle it is through
savings. So it's either made compulsory or you do end up with something of a
free loader problem. Whether that free loader problem is a real problem, I
don't know.

------
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

~~~
ianai
I wonder if there are maps of predictions of that.

------
idlewords
A similar thing has happened on the Mississippi river, which has had '500 year
floods' in at least 2011, 2009, 2008, 1993 and 1927. I may be missing a few.

Assigning probabilities to rare events is meaningless unless you a) have data
over a much longer time period than the recurrence time and b) the mechanism
causing flooding is not changing.

Neither of these holds in the case of Mississippi flooding, for which we only
have about 150 years of observations.

Unfortunately, multi-billion-dollar decisions about flood risk are made using
these manufactured numbers. For example, in Missouri, land behind a 100-year
levee is not required to have flood insurance.

~~~
maxerickson
Should any land be required to have flood insurance?

The NFIP supposedly reduces taxpayer cost (with the shaky risk management you
mention), but it currently has huge potential liabilities compared to the
premiums it collects (and owes the government a bunch of money from past
payouts).

~~~
cat199
Hey we've got a legal mandate to fund insurers now with our 'public private
partnership' healthcare system.. pick this up as your issue and you might have
a lucrative career in lobbying lined up..

~~~
matt4077
"Now"...

The National Flood Insurance Act of 1968 established the government-backed
flood insurance scheme. It has Ronald Reagan's signature.
[https://en.wikipedia.org/wiki/National_Flood_Insurance_Act_o...](https://en.wikipedia.org/wiki/National_Flood_Insurance_Act_of_1968)

The idea was and is twofold: first, it was seen as the only possibility to
actually provide such insurance because insurance companies (even together)
lack the financial strength to be able to insure risks that are statistically
extremely dependent. Something like this flood costs dozens of billions, and
it would bankrupt the whole industry.

Secondly, it's in the national interest to promote such schemes that allow for
more areas to be used productively.

~~~
HillaryBriss
> _insurance companies (even together) lack the financial strength_

high deductible policies and reinsurance are other tools that can be used to
help with this problem

------
rlglwx
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.

~~~
idlewords
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.

~~~
WorldMaker
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.

~~~
tedunangst
I don't know much about the field, but I'm curious. How much are estimates
based on normal distributions, and how much does the model consider other
distributions?

As you say, I don't think we know much about the tail. More than ten inches of
rain may be a once a year phenomenon, but that once a year event might be
twenty or fifty inches?

~~~
WorldMaker
Disclosure: I am not a subject matter expert, I just do the programming they
tell me to do. Mistakes/oversights here are likely my own, not my employer's
or the software I work on.

The rain gage analysis the software I work on does is largely based on USGS
data. [1] Almost all of that data is publicly accessible and you can explore
the data down to individual monitoring stations if you wander through the site
far enough.

The application I work with is primarily concerned with two bits of analysis
from the data in a given station: average peak annual flow and mean daily
flow. The distribution used for analysis of both (beyond linear interpolation
and best fit line options) is fitting to a Gamma distribution [2], and plotted
on a logarithmic scale. (Rainfall is specifically mentioned under applications
of that distribution on Wikipedia, so it seems to be the industry standard
even outside of the specific application(s) I work on.)

[1] [https://waterdata.usgs.gov/nwis/rt](https://waterdata.usgs.gov/nwis/rt)
[2]
[https://en.wikipedia.org/wiki/Gamma_distribution](https://en.wikipedia.org/wiki/Gamma_distribution)

------
mbroncano
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 anyone else in the world, but we don't invest
consistently on them anymore. Today our roads, dams etc. pale in comparison
with any western country's but it seems like it's an affront to our national
pride to acknowledge that.

Houston is ill prepared to face any kind of emergency like this one, and only
the bravery and tenacity of the people is preventing a humanitarian disaster
in the scale that would keep us awake at night. That's not the American way:
planning, preparing and executing is. The sooner we start taking this leap the
better.

~~~
pdq
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.

~~~
dlp211
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.

------
nyolfen
> The big news in the Galloway report, based on a global review of scientific
> and engineering data, was this: All of the money the United States had paid
> for massive public works to control flooding over the previous half-century
> not only had failed to improve flood safety at all, but the spending and the
> big public works projects actually were making flooding much worse.

> The Galloway report was no global warming screed. Like the Dutch national
> policy based on many of the same findings, it dealt almost entirely with
> land use and population growth. Or to put it in more accessible terms, the
> 'burbs.

[http://www.dallasobserver.com/news/harvey-not-only-can-
happe...](http://www.dallasobserver.com/news/harvey-not-only-can-happen-in-
dallas-it-will-9816590)

------
xexers
Anyone notice the comments for this article on WP? There appears to be a
poster called "The burning bush" who is commenting with lengthy comments about
every 6 minutes. All of the the comments from that user are sceptical of man
made climate change. Washington post does not appear to let you sort by
anything other than "newest"... which means that this commenter's posts are
always the top comment. That's concerning!

~~~
Applejinx
That's normal. You'll find the same thing going on in the HN comments for
'24/192K audio is silly': there's a class of people who fight for their
arguments not with science or discussion, but through brigading and
suppressing other people's arguments to get 'em out of sight. It's very much
the case with climate change denialists, and it's also in play with '16 bit
audio is enough for every possible person!' audio pundits: they will brigade
to suppress opposing arguments to make it seem like their views are unopposed.

Pretty sure the WP comments from the climate skeptics are more organized.
There's a lot more money in climate denialism, from traditional energy
companies with enormous resources and a clear agenda to continue their present
mode of operations. I've never understood why the 16-bit audio guys are so
similarly quixotic.

------
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.

~~~
tuna-piano
And the reinsurance folks seem to say that there is absolutely no evidence
that there has been an uptick in these big disastrous storms. People are
constantly thinking of global warming, so when they see a storm, they say
"Aha! Global Warming!". Of course there have always been hurricanes, and human
perception/remembering is not a replacement for statistics and math.

From Warren Buffet (One of the largest insurers of this type in the world)
"...climate change had not up until then [2016] produced more frequent nor
more costly hurricanes nor other weather-related events covered by
insurance.""

[https://www.cnbc.com/2017/02/27/warren-buffett-global-
warmin...](https://www.cnbc.com/2017/02/27/warren-buffett-global-warming-not-
impacting-berkshires-insurance-biz.html)

~~~
dogruck
Markets also did not collapse when Donny won. But, hey, what do markets know?

~~~
XorNot
They also didn't collapse till 2008. Then they did.

Markets are stupid.

~~~
dogruck
Do you have a suggested alternative guide and judge? Perhaps religious leaders
and liberal journalists?

------
staticelf
Bad shit happens when you fuck up the earths temperature. Why is anyone
surprised? This has been said by climate scientists all over the world many
times.

Warmer climate will result in more drought on some places and other stronger
storms which result in heavy rainfall and floods.

[https://climate.nasa.gov/effects/](https://climate.nasa.gov/effects/)

------
devy
Fort Bend County Judge Robert Hebert stated that Hurricane Harvey is more like
a 800-year event, as quoted from the statement from Monday, reported by the
same newspaper WaPo[1]

[1]: [https://www.washingtonpost.com/news/post-
nation/wp/2017/08/2...](https://www.washingtonpost.com/news/post-
nation/wp/2017/08/27/harvey-is-causing-epic-catastrophic-flooding-in-houston-
why-wasnt-the-city-evacuated/)

~~~
rsync
"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 unprecedented - Holland's dykes are designed and built to
withstand 10k year events:

[https://www.nytimes.com/interactive/2017/06/15/world/europe/...](https://www.nytimes.com/interactive/2017/06/15/world/europe/climate-
change-rotterdam.html)

~~~
Clubber
Sounds like the city fell asleep at the wheel, or rolled the dice and didn't
want to pay for proper drainage. Now the citizens get to pay.

Sounds like the Judge is preparing the country for the fact that nothing will
still be done about it.

~~~
21
There was an article from 2016 also on HN today about the risk. Three
different experts were quoted saying something along the lines "nothing will
be done now, we need to wait for the big flood and 2-4 years after we will
build a wall".

The "wall" (actually a more complex thing) was projected to cost 8 bil. A bad
flood like the one from today was projected to cost 70+, but people were
hoping that we have around 10-20 years to prepare

~~~
enraged_camel
Models actually showed a disaster of this scale as far back as 2005:
[http://www.chron.com/news/houston-texas/article/Models-
show-...](http://www.chron.com/news/houston-texas/article/Models-show-massive-
devastation-in-Houston-1950585.php)

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

~~~
21
He just tweeted about it:

"When people talk about 500 y floods or 100 year rain, they are klueless abt
tail distribution. The empirical distribution is NOT empirical!"

(and a picture with math equations)

[https://twitter.com/nntaleb/status/902632121407299585](https://twitter.com/nntaleb/status/902632121407299585)

~~~
vacri
The problem isn't the understanding of statistics, the problem is a grossly-
misleading name.

------
dmix
This article reminds me of Nate Silver's book [1] which has a far more
scientific and in depth look on the failure/success of these types of
predictive statistics.

The chapters on the many attempts (or many failed hopes) in predicting
earthquakes was particularly interesting, including many times the media has
bought into hyped up new charlatans who say they finally figured it out but
which ultimately failed to survive under basic statistical scrutiny.

It also has a useful soft introduction to Bayesian statistics and other useful
concepts from the field of prediction that I hope more journalists read about.
As this seems to be a very common theme in reporting.

Even this journalist couldn't help themselves with this line (combined with
some scary looking charts described with an alarmist tone farther down):

> Was there some miscalculation of how frequently these massive flooding
> events occur? Or, most alarmingly, is something else happening that suggests
> these catastrophic weather events are becoming much more common?

The failure to mention the effects of El Nino/El Nina seems like a big
oversight in this article, especially when we're just coming out of a
particularly strong one. Climate stats are an easy one to get wrong - or to
shape into any narrative - especially when timeframes and location are easy
things to be viewed too narrowly.

[1] [https://www.amazon.com/Signal-Noise-Many-Predictions-Fail-
bu...](https://www.amazon.com/Signal-Noise-Many-Predictions-Fail-
but/dp/0143125087/)

------
diafygi
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 currently focused on scale and growth[1], and we need as many
smart people as we can get. There are lots of companies hiring software
engineers.

==How do I find a job fighting climate change?==

I'd recommend browsing the exhibitor and speaker lists from the most recent
conference in each sector (linked below). Check out the companies that
interest you and see if they are hiring.

    
    
        * Energy Storage[2][3]
        * Solar[4][5]
        * Wind[6]
        * Nuclear[7]
        * Electric Utilities[8][9]
        * Electric vehicles[10]
    

Also, if you're in the SF bay area, I'd recommend subscribing to my Bay Area
Energy Events Calendar[11]. Just start showing up to events and you'll
probably find a job really quickly.

[1]: [https://techcrunch.com/2017/01/22/energy-is-the-new-new-
inte...](https://techcrunch.com/2017/01/22/energy-is-the-new-new-internet/)

[2]: [http://www.esnaexpo.com/](http://www.esnaexpo.com/)

[3]: [https://www.greentechmedia.com/events/live/u.s.-energy-
stora...](https://www.greentechmedia.com/events/live/u.s.-energy-storage-
summit-2016)

[4]: [https://www.intersolar.us/](https://www.intersolar.us/)

[5]:
[http://www.solarpowerinternational.com/](http://www.solarpowerinternational.com/)

[6]: [http://www.windpowerexpo.org/](http://www.windpowerexpo.org/)

[7]: [https://www.nei.org/Conferences](https://www.nei.org/Conferences)

[8]:
[http://www.distributech.com/index.html](http://www.distributech.com/index.html)

[9]: [https://www.greentechmedia.com/events/live/grid-edge-
world-f...](https://www.greentechmedia.com/events/live/grid-edge-world-
forum-2016)

[10]: [http://tec.ieee.org/](http://tec.ieee.org/)

[11]: [https://bayareaenergyevents.com/](https://bayareaenergyevents.com/)

~~~
jmcgough
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.

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

~~~
JamesBarney
Unless you're a lobbyist I feel like donations to lobbying organization would
have the greatest impact. Many politicians are bought for what is
comparetively a small amount of money compared to the impact they have.

------
jaclaz
There used to be a calculator by NOAA:

[http://www.srh.noaa.gov/epz/?n=wxcalc_floodperiod](http://www.srh.noaa.gov/epz/?n=wxcalc_floodperiod)

that is now here:

[https://www.weather.gov/epz/wxcalc_floodperiod](https://www.weather.gov/epz/wxcalc_floodperiod)

According to it, the probabilities of a 500 year event in the _next_ 500 years
is 63.2%.

What I like to call flippism point, i.e. when you have the same chances as
flipping a (perfect) coin is _next_ 346 years.

A three consecutive years series does seem a bit "queer".

------
Steve44
I saw a TV programme a year or two ago which was discussing the increase in
hurricanes etc in the Gulf of Mexico area.

They were saying that the storms aren't increasing due to global warming but
are actually regressing back to their natural levels. The previous decades of
pollution had been suppressing the storms and by cleaning the air the storm
ferocity is heading back to normal.

I can't see the article at the moment but I think it was Cloud Lab on the BBC,
they floated around on an airship.

------
blondie9x
[https://mobile.nytimes.com/2017/08/29/opinion/harvey-the-
sto...](https://mobile.nytimes.com/2017/08/29/opinion/harvey-the-storm-that-
humans-helped-cause.html)

On climates impact on extreme flooding.

~~~
mberning
"Some version of Harvey probably would have happened without climate change,
and we’ll never know the hypothetical truth."

But let me write an op-ed about it anyway.

------
twblalock
I hope the city will require houses to be elevated when rebuilt.

------
blondie9x
The fundamental takeaway from this article is about half way down. Major flood
events are occurint more frequently. What was once likely to hit a city every
500 years is happening to more cities on a planetary scale more frequently.

~~~
ars
I know it's easy to blame climate change for anything and everything, but
that's simply incorrect.

The actual takeaway is that our data is wrong, these floods occur more often
than we thought. With only 150 years of good data, it's impossible to
calculate "500 year" events accurately. You would need around 5,000 years of
data to do that, and we don't have it.

So we ended up significantly underestimating how often these events occur.

~~~
blondie9x
You can see in graph that floods are occurring more often and that clouds are
able to absorb more water as temperatures rise. This hurricane would have
happened. But this flooding is worsening because of climate change that is
irrefutable.

------
exabrial
Are random events evenly distributed? ......

------
cttet
Maximum likelihood ¯\\_(ツ)_/¯

------
VeronicaJJ123
I feel sad when people use statistics like this. It makes no sense to call
this 500 year flood because floods do not follow any kind of distribution. Not
to mention the human beings have been changing their environments drastically
in last 200 years.

NN Taleb would say this is fat tail event. It does not follow empirical
distribution.

------
dogruck
Is this like when reporters say, "Trump won. We now think that Clinton's lead
wasn't as strong as previously reported."

