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.
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).
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%.
Having lived in Houston, this isn't a measure of the flood but a measure of how terrible the infrastructure is. They have terrible flood management systems but are "rated" to handle everything but a "100" year flood... yet Houston gets 100 year floods every year- multiple ones- and has for 40 years.
It's a scam involving the ratings much like the mooody's ratings scam of the last decade IMNSHO
I understand your argument, but you can't compare floods to the birthday problem. Unlike randomly-sampled people's birthdays, floods in US cities are not independent random variables.
For instance, chances of 500-year floods in two Texas cities is not 1 out of 500*500 in a year. If they're geographically similar and physically close, it should be closer to 1 out of 500.
>> 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 in the last hundred years. It would seem the probably has gone up due to climate change, 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, and we have better records and better news transmission, but it certainly seems that can objectively say they're no longer 1-in-500 year flood regardless of the reason.
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.
A more accurate term for what you describe would be a clustering illusion[1], and it certainly could be a valid explanation (among other possibilities) for the observation made in the article.
Birthday paradox relies on non-independent events. I'd assume floods should be relatively independent between different cities, meaning that the number of 500-year flood events in the U.S. would follow a binomial distribution (https://en.wikipedia.org/wiki/Binomial_distribution).
p = 1/500 years = 0.002
For 100 cities, the probability of at least one city having a 500-year flood is 18.14%.
For a 3-year run:
p = (1/500)^3 = 8e-9
For 100 cities, the probability is 8e-7 of at least one success. For 1000 cities, the probability is still only 8e-6.
> 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.
Not quite the same because Huston is not the only city that has experienced extreme climate these two years, many other cities also have (maybe not 500 years flood, but close).
So that would be like: one pair is born the same day, and 20 other people in the room are born a week around that day.
Hardly a coincidence.
It's more likely that there was a party about 9 months and X years before that day. (I'm not sure how far we can go with this silly birthday analogy:)
I think that this statistic only makes sense if it is specific to the location. Otherwise, it is useless for planning purposes. If it is specific to the location then the birthday paradox does not apply.
Interesting note, this is Houstons third 500-year flood in three years [1].
> 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.
This is the key point here, and it's called the fallacy of multiple endpoints. If there are 500 observable cities, then somewhere among them should occur a "500-year event" every year. It's just that nobody ever notices the big bulk of the population that hasn't yet had any 500-year event in its recorded history.
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.
Ahem, no - your birthdays example can't apply here. When you increase the number of people in the room, each one of them benefits from every new person added, in terms of probability of having been born on the same day.
In the flood case, a flood in California and one in Miami don't really increase the chance of another flood simply because they have happened.
The "Birthday Problem" has a simple explanation. Something like nearly 45% of people are born in the Summer months. Ensure that you get people of different ages and your chances of finding someone with similar/same birthday goes up enormously.
But storms aren't people with randomly distributed cities to flood so you don't get the combinatorial effect. It's not like there are a fixed number of 500 year storms every 3 years that have to flood a uniformly distributed list of cities. The floods are supposedly independent (even if our estimates of likelihood are bad) so there's no binomial coeeficient.
The simple calculation is P=1-(1-1/500^3)^N and the probability is less than 1:10000 assuming independence and even given 6000 cities of a million people (the entire world population is in a similar city).
If it was birthday like (every possible 500 year storm for 3 years is in a room choosing out of 100 random million person cities), the probablility would be reasonable. You can use a Poisson distribution to estimate the 3 person birthday problem. P=1-exp(-3choose100/500^2)=48%
> 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.
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.
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.
Honestly I think it's easier to feel irrationally safe about a 0.2% chance, especially if you leave out the "per year". "500-year flood" at least emphasizes that it's not a question of "if", but "when".
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.
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.
> 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.
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!
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.
Every comments section I've seen for newspaper articles even in supposedly blue urban areas contain an outsize proportion of conservative trolls. It's possibly worse than youtube comments.
WaPo is experimenting with a new comment system, which is why it currently only lets you sort by newest. The old system had other sorting types, and the new one will too soon. Don't worry about it too much. :)
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.
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.
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]
And yes, basically we don't understand the actual probability of a "500-year storm", so our 0.2% chance per year is unreliable at best, more likely misleading.
Just like Europeans didn't know the actual probability of a black swan until they found them in Australia.
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.
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.
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.
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.
[+] [-] bkohlmann|8 years ago|reply
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|8 years ago|reply
[+] [-] waqf|8 years ago|reply
[+] [-] rothbardrand|8 years ago|reply
It's a scam involving the ratings much like the mooody's ratings scam of the last decade IMNSHO
[+] [-] pesfandiar|8 years ago|reply
For instance, chances of 500-year floods in two Texas cities is not 1 out of 500*500 in a year. If they're geographically similar and physically close, it should be closer to 1 out of 500.
[+] [-] TallGuyShort|8 years ago|reply
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 in the last hundred years. It would seem the probably has gone up due to climate change, 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, and we have better records and better news transmission, but it certainly seems that can objectively say they're no longer 1-in-500 year flood regardless of the reason.
[+] [-] ChadyWady|8 years ago|reply
[+] [-] curiousgeorgio|8 years ago|reply
[1] https://en.wikipedia.org/wiki/Clustering_illusion
[+] [-] hexane360|8 years ago|reply
p = 1/500 years = 0.002
For 100 cities, the probability of at least one city having a 500-year flood is 18.14%.
For a 3-year run:
p = (1/500)^3 = 8e-9
For 100 cities, the probability is 8e-7 of at least one success. For 1000 cities, the probability is still only 8e-6.
Wolfram alpha helps in calculating PDFs and CDFs: http://www.wolframalpha.com/input/?i=binomial+distribution+n...
[+] [-] bnegreve|8 years ago|reply
Not quite the same because Huston is not the only city that has experienced extreme climate these two years, many other cities also have (maybe not 500 years flood, but close).
So that would be like: one pair is born the same day, and 20 other people in the room are born a week around that day. Hardly a coincidence.
It's more likely that there was a party about 9 months and X years before that day. (I'm not sure how far we can go with this silly birthday analogy:)
[+] [-] epitomix|8 years ago|reply
Interesting note, this is Houstons third 500-year flood in three years [1].
[1] -https://www.washingtonpost.com/news/wonk/wp/2017/08/29/houst...
[+] [-] T-hawk|8 years ago|reply
This is the key point here, and it's called the fallacy of multiple endpoints. If there are 500 observable cities, then somewhere among them should occur a "500-year event" every year. It's just that nobody ever notices the big bulk of the population that hasn't yet had any 500-year event in its recorded history.
[+] [-] danmaz74|8 years ago|reply
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.
[+] [-] polotics|8 years ago|reply
[+] [-] simonebrunozzi|8 years ago|reply
In the flood case, a flood in California and one in Miami don't really increase the chance of another flood simply because they have happened.
[+] [-] SideburnsOfDoom|8 years ago|reply
Or rather, the odds of that kind of flood increase a bit each year.
[+] [-] dsfyu404ed|8 years ago|reply
[+] [-] walshemj|8 years ago|reply
[+] [-] oso2k|8 years ago|reply
[+] [-] kurthr|8 years ago|reply
The simple calculation is P=1-(1-1/500^3)^N and the probability is less than 1:10000 assuming independence and even given 6000 cities of a million people (the entire world population is in a similar city).
If it was birthday like (every possible 500 year storm for 3 years is in a room choosing out of 100 random million person cities), the probablility would be reasonable. You can use a Poisson distribution to estimate the 3 person birthday problem. P=1-exp(-3choose100/500^2)=48%
[+] [-] mirimir|8 years ago|reply
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|8 years ago|reply
[+] [-] idlewords|8 years ago|reply
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.
[+] [-] rlglwx|8 years ago|reply
That, my friends, is a prime example of the gambler's fallacy.
[+] [-] idlewords|8 years ago|reply
[+] [-] peeters|8 years ago|reply
[+] [-] mannykannot|8 years ago|reply
[+] [-] mbroncano|8 years ago|reply
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.
[+] [-] nyolfen|8 years ago|reply
> 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...
[+] [-] xexers|8 years ago|reply
[+] [-] Applejinx|8 years ago|reply
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.
[+] [-] stevenwoo|8 years ago|reply
[+] [-] 2sk21|8 years ago|reply
[+] [-] enraged_camel|8 years ago|reply
[+] [-] MarkMc|8 years ago|reply
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.
[+] [-] staticelf|8 years ago|reply
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/
[+] [-] devy|8 years ago|reply
[1]: https://www.washingtonpost.com/news/post-nation/wp/2017/08/2...
[+] [-] danielvf|8 years ago|reply
[+] [-] 21|8 years ago|reply
"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
[+] [-] kbutler|8 years ago|reply
And yes, basically we don't understand the actual probability of a "500-year storm", so our 0.2% chance per year is unreliable at best, more likely misleading.
Just like Europeans didn't know the actual probability of a black swan until they found them in Australia.
[+] [-] dmix|8 years ago|reply
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...
[+] [-] diafygi|8 years ago|reply
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.
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...
[2]: http://www.esnaexpo.com/
[3]: https://www.greentechmedia.com/events/live/u.s.-energy-stora...
[4]: https://www.intersolar.us/
[5]: http://www.solarpowerinternational.com/
[6]: http://www.windpowerexpo.org/
[7]: https://www.nei.org/Conferences
[8]: http://www.distributech.com/index.html
[9]: https://www.greentechmedia.com/events/live/grid-edge-world-f...
[10]: http://tec.ieee.org/
[11]: https://bayareaenergyevents.com/
[+] [-] jaclaz|8 years ago|reply
http://www.srh.noaa.gov/epz/?n=wxcalc_floodperiod
that is now here:
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|8 years ago|reply
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|8 years ago|reply
On climates impact on extreme flooding.
[+] [-] mberning|8 years ago|reply
But let me write an op-ed about it anyway.
[+] [-] twblalock|8 years ago|reply
[+] [-] blondie9x|8 years ago|reply
[+] [-] exabrial|8 years ago|reply
[+] [-] cttet|8 years ago|reply