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thunderhead
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PostWed Jun 05, 2019 2:59 pm 
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are you basing this on the assumption that gauges are still establishing a base set of data?

Of course.  If you have a gauge or river history that is 75 years old you have a 1 in 75 chance of breaking the previous record this year, assuming no trend.   Hitting 75 year flood boundaries every so often is not scary at all.  It is expected and normal.

Having portions of the Arkansas, the 20th largest river in the US by volume, break its record... again... not scary in the least.
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Parked Out
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PostWed Jun 05, 2019 7:20 pm 
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The 100-year flood concept explained by the USGS:

https://pubs.usgs.gov/gip/106/pdf/100-year-flood_041210web.pdf

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PostThu Jun 06, 2019 9:57 am 
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thunderhead wrote:
Of course.  If you have a gauge or river history that is 75 years old you have a 1 in 75 chance of breaking the previous record this year, assuming no trend.  Hitting 75 year flood boundaries every so often is not scary at all.  It is expected and normal.

Parked Out wrote:
The 100-year flood concept explained by the USGS:

https://pubs.usgs.gov/gip/106/pdf/100-year-flood_041210web.pdf


It's a shameful over-simplification of a complex problem. Again, these gauges are spread across disparate river systems, thus the annual exceedance probability is unique to each river system. Your method of AEP calculation assumes 1 record breaking event per 100 years for all gauges. Additionally, your method of AEP calculation is inclusive of all gauges, and assumes that all gauges have been in place for x years. A gross average of the aggregate shouldn't be relied upon, since this does not allow for accurate representation of outliers, contributing factors, patterns or variances, etc. It's ridiculous to shrug and say "it's all about chance".

The 1-100 annual exceedance probability is an arbitrary number, once again the gauges are spread out across individual river systems, setting a blanket AEP disregards this and ignores the unique datasets available for each system. Furthermore, the AEP itself should not be assumed to be a static value of 1-100 but can (should) change over time with the frequency of record level events.

Edit: PO, I'm still here to help you understand my response to your post of the "2017 US National Climate Assessment" graphic. Do you endorse each of the points made in that graphic?
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thunderhead
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PostThu Jun 06, 2019 11:13 am 
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Yes, its a simplification.  But a very good one.  The average annual probability of exceeding the previous record at any given location is equal to 1 divided by the period of record, in years, in a purely random system.  This is exact and indisputable.

Now, lumping all the guage ages together and rounding does introduce a minor amount of error, and 75 years is an estimate on my part.  Meh.  Close enough.

Even with no trend in flooding, given the size of the network and its age, we expect about 125 record exceedances in an average year of US floods.

Note, 100 year floods and record floods are not necessarily the same value.

The 100 year flood plain is also an estimate, sometimes a bad one based on a sample size that is not long enough.
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Doppelganger
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PostThu Jun 06, 2019 2:11 pm 
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thunderhead wrote:
equal to 1

How was this originally defined? Do you think it should still be a value of 1 after 50-60 years? Do you think a value of 1 should (accurately wink.gif ) apply to all 9050 gauges, or all river systems? I really am interested in knowing your thoughts on this as we pick apart the AEP.

thunderhead wrote:
in a purely random system

But we've established that it's not a random system, thus without performing this calculation for each river system or gauge, we can only establish (crudely) the collective probability of record flood events over time.

thunderhead wrote:
Meh.  Close enough. 

But is it good enough?  I still maintain that the simplified AEP equation does not account for any variables other than time, event recurrence within that time period, and number of stations. Thus the AEP equation is accordingly limited in function.
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thunderhead
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PostFri Jun 07, 2019 9:05 am 
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Excedence probability can indeed be made quite simple.   That's the point.   This is a pretty fundamental way of explaining risk with a simple set of stats that is robust and useful.   Yes, when one guage in a basin goes, the entire basin is likely to go and vice versa, a single guage being very much tied to its neighbors.  But that all washes out in the long term or large area average, and acts like a purely random system in aggregate.

Bottom line, we would need to see a lot more record setting and sustain that for years to say something unusual is occurring in the flood records.

For further proof of a neutral or near nuetral trend, we can bring up precip guages(no significant trend) and disaster damage(matching gdp growth).
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CC
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PostSun Jun 16, 2019 9:45 pm 
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MINNEAPOLIS (The Borowitz Report)—Scientists have discovered a powerful new strain of fact-resistant humans who are threatening the ability of Earth to sustain life, a sobering new study reports.
The research, conducted by the University of Minnesota, identifies a virulent strain of humans who are virtually immune to any form of verifiable knowledge, leaving scientists at a loss as to how to combat them.
“These humans appear to have all the faculties necessary to receive and process information,” Davis Logsdon, one of the scientists who contributed to the study, said. “And yet, somehow, they have developed defenses that, for all intents and purposes, have rendered those faculties totally inactive.”
More worryingly, Logsdon said, “As facts have multiplied, their defenses against those facts have only grown more powerful.”
While scientists have no clear understanding of the mechanisms that prevent the fact-resistant humans from absorbing data, they theorize that the strain may have developed the ability to intercept and discard information en route from the auditory nerve to the brain. “The normal functions of human consciousness have been completely nullified,” Logsdon said.
While reaffirming the gloomy assessments of the study, Logsdon held out hope that the threat of fact-resistant humans could be mitigated in the future. “Our research is very preliminary, but it’s possible that they will become more receptive to facts once they are in an environment without food, water, or oxygen,” he said.

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No matter how cynical you become, it's not enough to keep up.  Jane Wagner/Lily Tomlin
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MtnGoat
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PostMon Jun 17, 2019 10:09 am 
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Very timely article. Folks who intentionally subvert reason by refusing to accept falsification are indeed a danger to everyone around them. Such views are revealed by folks who do half science by claiming that positive evidence is all that matters, when in actual science, it is falsifying evidence which is the keystone of the process.

The folks mentioned in the article intentionally turn off their falsification receptors, while claiming that what agrees with their ideas is all that matters.

In reality, it is precisely the opposite. It is the falsified ideas which show you what is not true.

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Diplomacy is the art of saying 'Nice doggie' until you can find a rock. - Will Rogers
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joker
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PostMon Jun 17, 2019 11:06 am 
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We of course live our lives by many falsifiable theories which have not yet  been falsified.

Global warming is a falsifiable theory and it has not yet been falsified.
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MtnGoat
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PostMon Jun 17, 2019 11:09 am 
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joker wrote:
We of course live our lives by many falsifiable theories which have not yet  been falsified.

Global warming is a falsifiable theory and it has not yet been falsified.

It's amazing how much of it can be falsified while it's still not considered falsified.

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Diplomacy is the art of saying 'Nice doggie' until you can find a rock. - Will Rogers
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joker
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PostMon Jun 17, 2019 11:10 am 
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It's amazing how much vaguery one can see across the interwebz on the topic of falsification of GW.
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MtnGoat
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PostMon Jun 17, 2019 11:12 am 
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Yes, it is. The reality of logic however, is that regardless of how much frippery there is on the interwebs, truth still exists and it is what it is.

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Diplomacy is the art of saying 'Nice doggie' until you can find a rock. - Will Rogers
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joker
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PostMon Jun 17, 2019 11:20 am 
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On that statement, we agree.
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joker
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PostMon Jun 17, 2019 11:22 am 
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And one truth is that science is a matter of useful  theory more than it is of ultimate "truth"

The history of science has seen a progression from useful theories to yet more useful  theories as bits and pieces of falsification occur, for instance in the case of more precise measuring tools enabling subtler aspects to be theorized.
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RandyHiker
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PostMon Jun 17, 2019 5:14 pm 
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Science doesn't determine "ultimate truth" , which is more of a philosophical/religious concept.  Science develops "the most useful explanation so far for the available observations"

There is much confusion in popular thinking on this distinction.

"Ultimate Truth" has the same application to our daily lives as the discussions in the Middle Ages concerning the number of angels that can dance on the head of a pin.
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