Ecocentric

The Science Behind Colorado’s Thousand-Year Flood [CORRECTION]

How severe is the rainfall that has drenched Boulder over the past week? The city has already broken the record for annual precipitation—with more than three months left to go in the year

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Photo by Marc Piscotty/Getty Images

Record-breaking flooding has drenched Boulder and the surrounding areas of Colorado

Correction appended 9/20/13

Just a few months ago, Boulder, Colorado was in the grip of yet another drought, and the state itself experienced its worst wildfire on record earlier this year. But after days of heavy rainfall that the National Weather Service called “biblical,” drought and fire is the last thing that Boulder and the rest of the northern Front Range of Colorado has to worry about.

On average Boulder receives about 1.7 inches of rain during the month of September. As of 7 AM on September 16, Boulder had received 17.17 inches of rain so far in the month, smashing the all-time record of 9.59 inches set in May of 1995. 9.08 inches fell on Sept. 12, nearly doubling the previous daily record of 4.80 inches set on July 31, 1919. In fact, Boulder has already broken its yearly record for precipitation—with more than three months left in the year, and the rain still falling.

(PHOTOS: Intense Rains Cause Deadly Flash Floods in Northern Colorado)

Parts of Boulder are experiencing a 1-in-1,000 year flood. That doesn’t literally mean that the kind of rainfall seen over the past week only occurs once in a millennium. Rather, it means that a flood of this magnitude only has a 0.1% chance of happening in a given year. This is historically bad luck, due in part to the combination of an active, drenching Southwest monsoon and a low pressure area that trapped over the region. A tropical air mass—unusual in the dry Rocky Mountains—is slowly being hauled across the Front Range by weak southwesterly winds. This is known as an orographic lift, which is converting the incredibly moist air into sheets and sheets of rainfall.

Here’s how the weather blogger Dr. Jeff Masters described the flash flooding on Sept. 12:

The floods were triggered by widespread torrential rains of 4 – 6″ that fell in less than twelve hours, thanks to a flow of extremely moist air from the southeast that pushed up against the mountains. These sort of upslope rain events are so-named because as the air flows uphill, it expands and cools, forcing the moisture in it to fall as rain. Balloon soundings from Denver last night and this morning recorded the highest levels of September moisture on record for the station.

But as Adam Andrew Freedman of Climate Central noted, it wasn’t just weather that was playing a role in the biblical Colorado floods:

An increase in the frequency and intensity of extreme precipitation events is expected to take place even though annual precipitation amounts are projected to decrease in the Southwest. Colorado sits right along the dividing line between the areas where average annual precipitation is expected to increase, and the region that is expected to become drier as a result of climate change. That may translate into more frequent, sharp swings between drought and flood, as has recently been the case. Last year, after all, was Colorado’s second-driest on record, with the warmest spring and warmest summer on record, leading to an intense drought that is only just easing.

Climate scientists will surely try to find the fingerprints of global warming on the Colorado floods, though not immediately—the National Center for Atmospheric Research, a major Boulder-based climate research institution, had to be closed because of flooding. We’re not likely to have answers for awhile—it’s usually taken years for researchers to attribute extreme events to climate change, and the don’t always find the evidence. The more immediate need to rescue the thousands of people left stranded by the floods obviously takes precedence. But make no mistake—weather doesn’t get more extreme than what has happened to Colorado this month. For a disaster of this magnitude, once in a thousand years is still too common.

[Correction: I made a mistake here—it’s not that the Boulder area experienced a thousand-year flood event. Rather, it experienced what could be characterized as a thosuand-year rainfall event during the particularly intense periods of precipitation earlier this month. Floodwaters in fact did not reach those much higher levels. So what we had was epic rainfall that might be characterized as a thousand-year event—though scientists differ on the utility of using that term, given the paucity of older data from rainfall events—but nowhere near a similarly high flood. University of Colorado professor Roger Pielke Jr. pointed out the error in a post that you can see here:

A big problem with Time’s article is that Boulder did not actually experience a “1,000-year flood.” In fact, according to an analysis presented by fellow CU faculty member John Pitlick yesterday, using standard hydrological methods, Boulder experienced between a 25- and 50-year flood. (I am focusing here on Boulder, I have not seen similar analyses for other Colorado streamflows, though they are sure to come.) Pitlick further noted that the flood waters did not reach the 50-year flood marker on the Gilbert White memorial (seen at the top of this post.)

The Colorado floods were devastating by any measure, but it does no good to call it worse than it really is. My apologies.]

64 comments
EricAxelrod
EricAxelrod

Time,

You should be ashamed of yourselves on this error.  You do the cause way more harm then good with your inaccuracies.  Where are the editors?? This gives the deniers fuel to say look Time was lying just like Global warming denyers are lying.  Really frustrating guys

Eric Jericho, VT

EvanRavitz
EvanRavitz

Science means ACCURACY. We got a "1000-year" RAIN, not flood. Because it was spread out over 4-7 days, depending on your definition, the level of the flood was only "25-50-year" as measured by the 5,300 CFS maximum flow measured. We have a memorial on Boulder Creek at Broadway to Gilbert White, the "Father of Floodplain Planning" who started the CU Hazards Center and was awarded the National Medal of Science. The memorial shows the different flood levels. The water never went over the "50-year" mark.

j7t14r
j7t14r

If we safely recycle 100% of all human-generated waste materials, and peacefully reduce the human population with family planning programs, the weather will return to its normal seasonal patterns..

JuliusHenry
JuliusHenry

Although, not encompassing as large an area or the magnitude of death and destruction as say the 1965, the 1935, the 1921 or the 1865 Flood, it is going to be called a "1000" year flood? It might be in the top 10 of Colorado floods, but I doubt it's in the top three. We even have had extremely bad September flood before in recent history, in 1970, although that one is barely in the top twenty of Colorado's most damaging floods.
Also one might read about the Lost Engine of Kiowa Crossing, a 50 ton locomotive lost in a flood in 1878, and never found. (Legend has it).

AndrewRoberts
AndrewRoberts

Don't people move to Colorado to avoid natural disasters? 

gad_E
gad_E

Using science to describe an event that is also characterized as "biblical" is borderline hilarious.

billwitten
billwitten

Global warming....isn't.  It isn't happening, it isn't man-made, it just ISN'T.  Climate change, the new buzz word, was a safe way to go.  Climate changes daily, right NCAR?  Well, they can't be blamed.  After the entire world, except for a few of the true believers, has seen that Global Warming was a Global Hoax intended to divert funds into the pockets of the people that set up the scam.  The researchers with their lucrative grants and the politicians with their carbon credit business and the governments with their carbon taxes were all beneficiaries of the fraud.

The losers were real scientists that believe in that whole "outdated" scientific method "crap" and the people that were dumb enough to buy into it (and some still do!)--not to mention taxpayers, in general.

iluv2skico2
iluv2skico2

Anthropogenic climate change really is a state sponsored religion.  It's complete with priests at NCAR and U. of East Anglia.  Its chapels are the schoolhouse, its temples the statehouse, its seminaries the various campuses of higher education.  It has Man-Bear-Pig evangelizers living large and jetting off to Davos in their G5 to predict the latest cataclysmic outcomes if the heathens don't repent.  Surely we'll be ruined if the rest of us don't surrender to the statists at the UN who would expropriate our remaining life choices. 

And, of course, like all centralized great religions, it has its dark underbelly.  In its vaults lies evidence of data tampering, specious "normalizing" of raw data followed by raw data destruction.  We find Machiavellian plots to suppress evidence that challenges the religion's basic tenants such as the two decades of climate stability that broke their predictive models. All religions require enforcement to persist.  The way they ostracize and excommunicate dissident thinkers or agnostics would make Galileo's persecutors blush.  Apostates can kiss their grants and ability to publish forever goodbye.

Beneath the religion's bureaucracy lies the great unwashed laity, buttered and broiled throughout their formative years by the indoctrinating liberal orthodoxy in the public school system.  The utter intellectual abuse at the hands of these derelicts has resulted in a generation lost.  Devoid of healthy skepticism and critical thinking skills, they are programmed to reflexively outsource their most important responsibilities as a citizen to the orthodox priesthood.  When told that fracking or burning natural gas is bad, they accept it without reservation or so much as glance of the mountain of evidence to the contrary.  Like pawns on a chessboard, they perform their assigned duties, procreate and die.

iluv2skico2
iluv2skico2

Are these the same Climate Scientologists who two years ago predicted the catastrophic loss of arctic ice mass by 2015?  The same clowns that freaked out the kiddos with stories of cuddly polar bears drowning?  Now that the arctic ice mass is 60% larger and closing down the lifeblood Behring Sea fisheries, where are the alarmists now?

4ever49
4ever49

Oh the irony - NCAR (National Center for Atmospheric Science) closed due to rain storm and subsequent flooding. If anyone should have been able to see this coming it should have been -- wait for it -- NCAR!!

But now we must listen to them wax poetic about global warming, etc. and all the measures we must undertake to avert disaster.

Enough already.

JohnDahodi
JohnDahodi

The carnage caused by the 1000 year flood in Colorado is devastating and severe for millionof habitats. It is beyond expression how much pain and sufferings it has caused to them, and how long? How many of them will be displaced and how many will reverse of their fortuneovernight? But it was not carried out due to human acts, it was nature's call, no one can stop. 

But, can we take a deep breathe and think for a while; if the Obama has carried out his unending war game using Tomahawk missiles on Syria, just to satisfy his ego; and caused destruction more than what the flood in Colorado and fire in New Jersey Shore has caused; how he would have slept for the rest of his life? And, we Americans would not have been responsible for the pain and sufferings caused to these innocent and unfortunate human beings?

Nature is punishing us by way of earthquakes, flood, fire and so many natural disasters, and we have no power to stop it, but can we stop our own acts which can cause such destruction, pain and sufferings?Instead we should spread Humanity, love, peaceful co-existence, affection, brotherhood, compassion, justice and fairness among all to make our life pleasant and livable.   

emmonak1
emmonak1

the   world's    weather  pattern  is  changing.

GeneGrode
GeneGrode

It is all from God, who gave man guns and is now upset at the politicians of Colorado trying to take them away.


mrsoltys
mrsoltys

I agree with @EvanRavitz , This article from the title-onward is riddled with errors.  As we're discussing rain events: realize that this storm maxed out at 1"/hour around boulder.  In 1976 the Big Thompson flood received 8"/hour just a few miles north of here.  And in 1894 boulder creek reached somewhere between 11,000 and 13,000 cfs: more than double the streamflow we saw in this flood.

I'm not saying that the damage done was not very real.  This flood was horrible. I have many friends who lost possessions and their homes in this flood; but to inaccurately assess this flood's magnitude is to be unprepared for future events.

Finally, as a scientist in water resources, I do believe that climate change increases chances of extreme weather events.  However, trying to link this event to climate change is sensationalistic.  We simply do not have enough historical data to begin to make that connection, and this type of reporting feeds the skepticism in facts that we do have very real data to back up.

rpearlston
rpearlston

@gad_E THe hilarity isn't found in the weather, but is a part of your example.  And yes, it's a common idiom in many English-speaking parts of the world.  It may also be an idiom in other countries that have been influenced by "christian" values, good, bad and horrific.

terripeate
terripeate

@gad_ENot at all. Slightly ironic perhaps, but it's a common enough idiom in English. It refers to the scope of something, and doesn't suggest any supernatural cause.

JenniferBonin
JenniferBonin

@billwitten"Climate changes daily, right NCAR?"

No.  WEATHER changes daily.  CLIMATE is something different.  The guys at NCAR understand that, unlike you.

rpearlston
rpearlston

@billwitten Your so-called "true believers" are true believers in their (your) own paranoia.  Once you decide to stop drinking the Kool-Ade, your eyes will be truly opened and you'll be able to see that how much nonsense you've been spouting.

TheInsomniac
TheInsomniac

@billwitten Your ignorance is appalling. Anyone with such a minuscule level of knowledge of a subject should feel ashamed to open their mouth and comment. Lack of shame may be the defining characteristic of our age, and you are perfectly representative of it.

evenhanded
evenhanded

@iluv2skico2 Apparently you have not a clue about the difference between science and religion.  But you do have quite the ability for writing a load of nonsense.  You suggest that there is a mountain of evidence to the contrary about fracking.  What kind of evidence would that be?  Science is only valid if YOU agree with it?  You've become the judge and jury...with what qualifications?  Everything you write is a lie...so maybe, that is your chief qualification.  How many apostates can you name that have lost their ability to get grants forever?  Liar.

rpearlston
rpearlston

@iluv2skico2 Stop trying to mislead the world.  Your so-called point of view is mired din a complete and utter lack of education in the sciences in general, something that dangerous to everyone.  Your voice doesn't belong in public spaces.

terripeate
terripeate

@iluv2skico2 When religious people really want to insult something, they imply it's a religion. This eloquently shows the low esteem to which religion has fallen.

JenniferBonin
JenniferBonin

@iluv2skico2 *sigh*  Let's say that you are a very poor person making $1/day at your job.  Then you get a 60% raise.  Now you make $1.60 each week.  Does that 60% increase make you rich?  Or are you still quite poor?

Because that's the comparison you're making.  A 60% increase of ice from one year to the next means going from the historical low to something that's only very low, not historically low.  More, that increase says NOTHING about what the ice extent is going to be next year, or ten years from now.  It is not a statistically robust number, which is why scientists aren't saying much of anything about it.  Only the media and the climate skeptics (neither of whom know much about actual climate variability) are claiming it's anything more meaningful than a single data point in a long line of data.

terripeate
terripeate

@iluv2skico2 Learn the difference between surface area and volume. This whole ice increase claim has been thoroughly debunked by now, but we'll be hearing it from devout denialists for years to come.

rpearlston
rpearlston

@4ever49 Enough already from the deliberately science-ignorant such as yourself.

terripeate
terripeate

@4ever49 What do you think they should have done? Move the building? It is situated on a plateau completely unaffected by the current flooding, but streets giving access were flooded. Nothing useful or of significance has been developed by guys sitting home in their underwear, typing comments on the web.

rpearlston
rpearlston

@JohnDahodi Stop conflating things that have absolutely nothing whatsoever to do with one another.  and no, this has nothing to do with revenge from some "supernatural" (and completely non-existant) deity.

terripeate
terripeate

@JohnDahodiNature has no intentionality. This differs is only slightly from the rants of the Bible-thumpers claiming it is God's wrath for the wickedness of Boulder.

JackWolf
JackWolf

@JohnDahodi All that wont stop global climate change no matter how much hope you have.

And as to NCAR, they should have known not to build on floodplain or old stream terraces especially with their knowledge of expected impacts of climate change.  This is just like NYC's Response Group being in the Twin Towers on 9/11 and VT DEP's HQ on a flood plain - placing public assets in harms way when needed most is an expense we can't afford. 

JenniferBonin
JenniferBonin

@emmonak1 *sigh*  Perhaps, but this is not evidence of it.  Please don't play 'chicken little' when there's no evidence to support what you're saying.  There's a big, big difference between long-term climate change and short-term weather impacts.

DanSmith
DanSmith

@emmonak1 It has been changing for 6 billion years and will keep changing,whether we are here or not


eagle11772
eagle11772

@emmonak1 It always does.  I guess you haven't heard about humans living thru what were called "Ice Ages".

gorks4yes
gorks4yes

@GeneGrode 

Then, God must really hate Republicans because you know, Louisiana, Alabama, Florida, Texas are frequently getting hit by hurricanes...

:-\

terripeate
terripeate

@GeneGrode God does not exist, and the idea he does and gave Man guns constitutes a double delusion. Of course, you are being sarcastic.

CalvinHuang
CalvinHuang

@TheInsomniac @billwitten This is a classic example of the Dunning-Kruger effect and illusory superiority. Clearly he's smarter than the world's top climatologists and atmospheric scientists. Only a true genius would realize that scientists who stay in academia where there is more competition, more demanding hours, and lower pay than in industry are the greedy, unscrupulous ones, making up false scientific models for money, while the private sector scientists paid huge sums by the oil industry are the truly objective and unbiased ones.

And who wouldn't trust climate-change-denialist organizations that are chaired by people with business/marketing/economics degrees and sport titles like VP of Marketing at Exxon Mobil or CFO of BP rather than U.N. scientists who have been researching climate change for decades.

gorks4yes
gorks4yes

@JenniferBonin

There is evidence that long-term climate change is occurring, though this single Colorado flood may not be it -- we won't know until we see a trend.

So I give you the Red River in North Dakota. It has had a cluster of 100-year floods in the last decade.  If you look at this NDSU plot of the Red River peak discharges, you can quickly see this effect.  Then this other plot of daily mean flow rates shows just how dramatic the change has been.  Notice how flood stage levels have been reached out of season, frequently in the last decade.

 For kicks, you can also see the Dust Bowl in that last plot, actually.


evenhanded
evenhanded

@DanSmith @emmonak1 Here's some info for someone who doesn't have a clue:

the definition of climate: the average course or condition of the weather at a place usually over a period of years as exhibited by temperature, wind velocity, and precipitation.   

Yes, climate does change over time, so what does it matter?  What matters is the speed of change.  Life...the ecology of any particular location, is adapted to the "recent" climate.  If the climate changes slowly, the ecology can adapt to that change.  If the climate changes rapidly, the ecology can't keep up and extinctions multiply.  The problem with the current situation is the speed of change.  Extinctions rivaling the mass extinctions of the past are becoming more likely as CO2 and other greenhouse gases continue to build up.  And yet, every day people like you pretend it's all good...don't worry...deny, deny, deny.  

gorks4yes
gorks4yes

@eagle11772

The period between ice ages is measured by hundreds of millions of years; the interglacial period is approx. 100K years.  If temperature change and CO2 go hand in hand, then you have to be at least slightly concerned that CO2 levels are now significantly higher than it has ever been in 3M years.

evenhanded
evenhanded

@DanSmith @rpearlston @billwitten Hey Dan...nice try, but wrong again.  Scientists were not predicting exactly when another ice age would start...no one knows exactly what caused the last one, so who knows when another one would start.  It was the media that transformed misunderstood comments into a scare to sell a story!  Wow, imagine that.  From...sure, the next ice age could start tomorrow or 1,000 yrs from now...no one knows....became "Scientists predict the next ice could start any day now."  And, since you are obviously a denier, and would jump on the idea that another ice age may happen any day now....good news.  We have enough CO2 in the air to preclude another ice age of the same magnitude as the last one.  We are safe from the cold...the heat is another matter.

gorks4yes
gorks4yes

@JenniferBonin Oh, and yes, the anti-Dust Bowl condition did cross my mind, which is why I mentioned the Dust Bowl appearance in the plot.

BUT, the onset of the Dust Bowl is sudden and clear, whereas the current flooding trend has been growing for the last two decades.  Just look at the last two years in the plot, and it shows extensive, unseasonal flooding.

gorks4yes
gorks4yes

@JenniferBonin

Just curious, what confidence level in the statistical correlation do you need, to believe?  100%?

JenniferBonin
JenniferBonin

As an example of what I mean by non-robust statistics, ask yourself:  How do you know that what's happening now isn't just an "anti-dustbowl"?  Since we don't know the root cause of the Dustbowl, how can we know the opposite isn't happening now, naturally?

JenniferBonin
JenniferBonin

@gorks4yes @JenniferBonin I know climate change is happening.  I'm a scientist who studies mass loss in Greenland.  There's no doubt it's happening.

But the records of any particular river aren't good evidence of that, and nor are things like hurricane records.  Why?  Because they don't go back far enough to give us confidence that what we're seeing isn't a sort of century-scale variability.  For example, did you know that in the early 1900s, the number of recorded land-falling hurricanes in the US swamps anything we've seen in the last 50 years?  So we KNOW that weather has patterns of high periods and low periods in precipitation, and we don't know what causes those changes.  So all we can say is that it would make sense, logically, for more storms and precipitation to occur because of climate change, but we can't prove, statistically, that that's really what's happening.  It's not a statistically strong correlation.  That makes it an interesting thing to study, but NOT a proven fact to brag about to climate denialists.  It makes a lot more sense to make arguments about things which ARE statistically robust instead, of which there are many.

gorks4yes
gorks4yes

@MarkEast

Apparently I left out a word that made my point less than clear.

"The period between ice ages is measured by hundreds of millions of years; between the interglacial period is approx. 100K years."

Clear now?

MarkEast
MarkEast

@JackWolf @eagle11772 @gorks4yes  

 Nope, eagle is correct, and gorks is mostly wrong. 

This interglacial, the Holocene, has indeed lasted about 10,000 years (and, incidentally, in the early stages was warmer than now, with at least periods of an ice free north pole - ironically enough, this was named the Holocene Optimum).

The interglacial prior to the Holocene, the Eemian, ended about 120,000 years ago, and was a couple of degrees warmer than now, and lasted about 14,000 years.

Over the last 500,000 years interglacials have lasted 5,000 to 15,000 years, and the glacials about 120,000 years. 

Technically speaking, we are still in an "Ice Age", which is the occurrence of ice at one or both poles. 

In the total history of the planet this is a rather rare happening.

eagle11772
eagle11772

@gorks4yes  The last ice age ended about 10,000 - 12,000 years ago.  NOT the hundreds of millions of years ago you suggest.