News Section
Stories from Climate Central's Science Journalists and Content Partners

Colorado’s ‘Biblical’ Flood in Line with Climate Trends

Repost This

The Boulder, Colo., area is reeling after being inundated by record rainfall, with more than half a year’s worth of rain falling over the past three days. During those three days, 24-hour rainfall totals of between 8 and 10 inches across much of the Boulder area were enough to qualify this storm as a 1 in 1,000 year event, meaning that it has a 0.1 percent chance of occurring in a given year.

A scene of flooding in Colorado.
Credit: nathancheta/Instagram

At least four people have been confirmed dead so far with many more still missing, and thousands have been evacuated from their homes and businesses. All along Colorado’s Front Range from Denver northward to Boulder and in nearby areas, small creeks have been transformed into raging rivers, and surges of water, mud, and debris have blasted their way through canyons, at one point trapping a firefighter on a treetop before being rescued. Numerous longstanding records have been smashed, including the all-time 24-hour rainfall record in Boulder. 

“This is clearly going to be a historic event," National Weather Service Director Louis Uccellini said in an interview. “The true magnitude is really just becoming obvious now.” 

Uccellini said the Weather Service has initiated a review of its performance leading up to and during the event. Although the potential for heavy rainfall was in the agency's forecasts a week in advance, he said, “Clearly the magnitude of the rainfall and the repetivieness of it in some critical areas was not pinpointed” well ahead of time. Uccellini said that this event will be the new historical high water mark for many affected rivers and streams. In a technical discussion on Thursday, the NWS described the rainfall amounts as "biblical."

On average, Boulder gets about 1.7 inches of rain during September, based on the 1981-2010 average. So far this month, Boulder has received 12.3 inches of rain. This smashes the record for the wettest month ever in Boulder, which was set in May 1995 when 9.59 inches of precipitation fell — and September isn’t even half over! Not only that, but the average yearly rainfall in Boulder is 20.68 inches. This means that Boulder picked up well over half its annual precipitation in just a couple of days. 

This comes on the heels of a summer when Boulder experienced a moderate drought according to the U.S. Drought Monitor. This summer also featured the Colorado's most destructive wildfire on record.

Slideshow

During the past couple of weeks, the weather across the West has featured both an active Southwest Monsoon and a broad area of low pressure at upper levels of the atmosphere, which has been pinned by other weather systems and prevented from moving out of the region. It was this persistent low pressure area that helped pull the moisture out of the tropics and into Colorado. Signs point to the tropical Pacific being the source of the abundant moisture according to the University of Wisconsin’s Cooperative Institute for Meteorological Satellite Studies. From there, the moisture plume was transported northeastward, over Mexico and into Texas, and then northward by upper level winds.

This tropical air mass, which is more typical of the Gulf Coast than the Rocky Mountains, has been forced to move slowly up and over the Front Range by light southeasterly winds. This lifting process, known as orographic lift, allowed the atmosphere to wring out this unusually bountiful stream of moist air, dumping torrents of rain on the Boulder area for days on end. There was also broader-scale lifting of the air that resulted in heavy rain in areas of eastern Colorado and western Kansas as well.

According to meteorologist Jeff Masters of Weather Underground, the amount of moisture in the atmosphere, or "precipitable water," as measured by a weather balloon over Denver on September 12, reached record values for the month of September.


Water vapor satellite loop from Sept. 12, 2013 showing the plume of moisture directed at Colorado.
Credit: CIMSS

The National Weather Service (NWS) said in an online discussion on Friday that the amount of precipitable water in the air over Colorado is still at record levels for this time of year, which is an indication that the potential for heavy rainfall remains high.

Colorado has a long and tragic history of flash flood events, most notably the Big Thomson Canyon Flood in 1976, which resulted in 139 deaths after a slow-moving thunderstorm dumped a foot of rain in just four and a half hours, causing a massive wall of water to blast through the canyon. According to the NWS forecast office in Denver/Boulder, the river stage at the North Fork of the Big Thompson river so far has exceeded the Big Thompson Flood of 1976 by more than 1 foot.

Enough rain fell between Sept. 10-12 to turn 2013 from one of Boulder's driest years into a year that, so far, is rivaling its wettest on record.
Click image to enlarge. Credit: Dennis Adams-Smith/Climate Central.

Did Climate Change Make This Event More Likely?

It will take climate scientists many months to complete studies into whether manmade global warming made the Boulder flood more likely to occur, but the amount by which this event has exceeded past events suggests that manmade warming may have played some role by making the event worse than it would have otherwise been.

Considering that this flood event occurred in the backyard of some of the world's top climate researchers, it is likely that this event will be closely researched. Boulder is home to several major weather and climate research institutions, including the National Center for Atmospheric Research and the Earth System Research Laboratory, both of which were forced to close due to flooding.

Extreme rainfall events have become more frequent across the U.S. during the past several decades in part due to manmade global warming. Increasing air and ocean temperatures mean that the air is generally carrying more water vapor than it used to, and this moisture can be tapped by storm systems to yield rain or snow extremes. Trends in extreme precipitation events vary by region, though, and in general the biggest increases have taken place in the Midwest and Northeast. However, most parts of the U.S. have seen an increase in extreme precipitation events, according to the draft National Climate Assessment report that was released this past January. The report goes on to note that in the future, "increases in the frequency and intensity of extreme precipitation events are projected for most U.S. areas.”

The increase in the most extreme precipitation events (99th percentile) since 1950.
Click image to enlarge. Credit: Climate Central/National Climate Assessment

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. 

Although the overall climate of the Southwest may become drier over the coming decades, a greater proportion of the rain that does fall could be in the form of heavy precipitation events. “. . .  Heavy downpours will account for increasingly large portions of the total precipitation in regions such as the Southwest, where total precipitation is projected to decrease,” the report said.

Previous studies have found that global warming made some extreme rainfall and flood events more likely, including major flooding in the U.K. in 2000. Some recent work has found mixed evidence about whether warming played a significant role in other flood events, though, such as the Queensland floods in Australia in 2011-12.

The biggest and most consequential rise in flood risk may take place outside the U.S., in countries that don’t have as much of a capacity to bounce back from such disasters, however. A study published in the journal Nature Climate Change on June 9 found that flood frequency as well as the number of people at risk of inundation from flood events are both likely to increase as the world continues to warm, but most especially in developing countries in Southeast and South Asia. 

Related Content
Report Ties Climate to Extreme Events, But Shows Hurdles
5
 Must-See Charts From Major New U.S. Climate Report
New Reports Show Impact of Manmade Global Warming
As Calgary Floods, Scientists Warn of Rising Risks
Did Climate Change Set the Stage for Duluth Flooding?
Scientists Identify Human Connection to Precipitation Extremes
Is Climate Change Causing the Mississippi River Flooding?
Historical Context of the Mississippi River Floods
'Strong' Links of Manmade Heat, Rainfall Extremes

Comments

By Steve Goddard (Fort Collins CO 80525)
on September 13th, 2013

The USGS says this is a 100 year flood, not a thousand year flood as claimed in this article.

“Longstanding rainfall records were swept away in what an official with the United States Geological Survey late Thursday confirmed was for Boulder a 100-year flood—although that agency no longer uses that term.
We’re getting away from using that terminology, because people tend to think that’s the storm that happens every 100 years,” said Robert Kimbrough, associate director of the USGS Colorado Water Science Center. “But really, it’s the chance of it happening in any given year is one in 100.”

http://www.dailycamera.com/news/boulder/ci_24081189/flood-expert-boulder-experiencing-100-year-flood

Despite all the hype, it is a spectacularly beautiful day here in Fort Collins and the only thing preventing life from being normal are the completely unnecessary barricades set up by the city.

Reply to this comment

By Andrew
on September 13th, 2013

Hi Steve,

The 1,000 year figure comes from NOAA data comparing rainfall totals with their statistical frequency tables and data found via: http://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=co

The article you referenced was published yday, when it was STILL raining.

 

Reply to this comment

By Steve Goddard (Fort Collins CO 80525)
on September 13th, 2013

A USGS guy posted this on my blog

“geologyjim says:
September 13, 2013 at 9:02 pm
There’s a monument along Boulder Creek dedicated to Gilbert White, hydrologist, that shows the altitude of projected 50-year, 100-year, and 500-year flood crests.

On the Channel 7 news this morning, the flow level was below the 100-year gage”

Reply to this comment

By Andrew
on September 13th, 2013

Ah, but the story doesn’t state that it was a 1,000 year flood, rather it’s talking about rainfall amounts in that instance. But thanks for relating the gripping account from geologyjim.

Reply to this comment

By David Richter (80203)
on September 13th, 2013

Title of your article “...in Line with Climate Trends” seems a bit over the top to me considering the uncertainty associated with the claim. Sure, it *may* be, but even the 12% likelyhood of such events in this region suggests there isn’t enough to attribute such a monsoonal event on climate change. I’d rather see data indicating the variability of the typical monsoonal events across the SW US has really changed (seem)s the sub-trop Pac moisture flow isn’t usually around this time of year). But we all have seem big fat thunderstorms sit over the Front Range, isolated from mid-lat flow, for a very long time. Don’t recall anyone pinning those to climate change before.

Reply to this comment

By Andrew
on September 13th, 2013

Hi David - your comment on uncertainty is a good one, but I’m not sure this event was sufficiently monsoonal in origin, considering the front draped across the Front Range, the sprawling upper low, and the tropical systems near Mexico, to make that an apples to apples comparison.

Reply to this comment

By Steve Goddard (Fort Collins CO 80525)
on September 13th, 2013

The 1976 Big Thompson River flood brought 12 inches of rain in only 4 hours. It was much more intense than what we have had this week. Same for the 1972 Rapid City, SD flood.

I don’t buy the statistics. They are not even remotely credible

Reply to this comment

By Andrew
on September 13th, 2013

The 1976 flood was the result of a thunderstorm that sat over a small area. This event occurred over a far broader region, and from totally different atmospheric dynamics. Also the Rapid City flood was in South Dakota, which the last time I checked, is not in Colorado.

Reply to this comment

By climatehawk1 (Norwich, VT 05055)
on September 13th, 2013

Note, massive flood recently along Russia-China border. Amur River level exceeded 116-year-old record by two meters. http://thinkprogress.org/climate/2013/09/10/2597341/historic-flooding-russian-chinese-border/

Reply to this comment

By Mauri Pelto (West Boylston)
on September 14th, 2013

The widespread nature of this flood combined with the magnitude makes this a larger flood event than Big Thompson in 1976, which I was in the state to witness.  This is obviously a quite rare event.  the Calgary region of Alberta experienced a similar event in June.  It was not the same type of storm, but equally unusual.  From Chris Burt Heavy rainfall began falling across the Bow River Basin on Wednesday night with up to 190 mm (7.51”) falling in some areas over just a 24-hour period. However, it was the widespread nature of the heavy rainfall, with an average of 50 mm (2”) blanketing the entire river basin that has led to the massive flooding.”  The Calgary event also featured a rare rain on snow event higher in the mountains for the second consecutive year, combined with high intensity.  I could go on with the unusual rain events in the North Cascades of Washington from this summer.

Reply to this comment

By Fred Bauder (Crestone, Colorado 81131)
on September 14th, 2013

Yes, if the oceans and atmosphere are warmer there will be more energy and water vapor in the atmosphere. So there will be more total rain and more energy released when it does. However, despite the dramatic events of last week, resulting mostly from many thousands of people living in canyons and floodplains, such downpours are normal, if rare. Just as the only thing that separates the high plains from the pole is a single strand of barb wire; the only thing that separates the Front Range from the Gulf of Mexico is a patch of broom corn and a dead cow.

Reply to this comment

By richard pauli (Seattle, Wa. 98119)
on September 14th, 2013

Great article and nice comment dialogue

Thanks for putting this all together.

Reply to this comment

By Gail Zawacki (Oldwick NJ)
on September 14th, 2013

Not to minimize extreme precipitation from climate change, but it’s worth noting that many reports (such as this one:  http://www.nbcnews.com/science/scars-left-wildfires-worsen-flooding-colorado-8C11137866) link some of the cause of flooding to land denuded of vegetation from wildfires.

The wildfires are themselves a direct result of trees and other plants dying prematurely from air pollution.  In many of the images in the news from the floods, dead trees are plainly visible - the photograph above with the caption “Someone trying to swim…” is an excellent example.

And no, it’s not just drought from climate change because the trees in areas that are getting wetter, not drier, from climate change (such as the Eastern seaboard and the UK and Scandinavia) are in equally poor health.  For more information see:  http://scienceblogs.com/gregladen/2013/01/29/whispers-from-the-ghosting-trees/ and/or http://witsendnj.blogspot.com/

Declining forests from air pollution should be of critical interest to climate scientists and activists because without their role as a CO2 sink (aside from all the other ecosystem services they provide) global warming is going to accelerate exponentially and become a true existential threat.

The death of trees is also a powerful motivator for people to understand the drastic reduction in emissions (i.e. consumption and population) required if we are to avert (or just delay) disaster.

Reply to this comment

By E. A. Grace
on September 14th, 2013

The Weather Channel has posted an article titled, “Colorado Flash Flooding: How It Happened, How Unusual?”, which states:

“The atmospheric setup … consisted of an upper-level low pressure center over the Great Basin, blocked from moving east or north by a large dome of high pressure aloft over the Pacific Northwest and southwest Canada.”

http://www.weather.com/news/weather-severe/colorado-flash-flood-how-it-happened-unusual-20130912

In your article, “How Global Warming Made Hurricane Sandy Worse”, you state:

“The upper-air flow over the Atlantic Ocean was temporarily jammed by a powerful area of high pressure near Greenland and a storm system in the Central Atlantic, leaving the storm no escape route away from the U.S. Such patterns are known as “blocking” events, and they have occurred with increasing regularity and intensity in recent years. Blocking patterns have been linked to several noteworthy extreme weather events, such as the deadly 2010 Russian heat wave and Pakistan floods, the 2003 European heat wave, and the March heat wave of 2012 in the U.S.”

http://www.climatecentral.org/news/how-global-warming-made-hurricane-sandy-worse-15190

Are the recent heavy rains in Colorado, then, another example of such blocking events (the increased frequency of which, as you mention in your article on Sandy, may possibly be linked to the loss of Arctic sea ice)?

Reply to this comment

By climatehawk1 (Norwich, VT 05055)
on September 14th, 2013

However, as the map above makes clear, while any individual event may not be beyond the bounds of what has happened before, the frequency is unusual and increasing. We have had a number of remarkable flood events in the past decade around the world. They are becoming less and less rare.

Reply to this comment

By Andrew
on September 14th, 2013

E.A. Grace: This event is indeed another example of the extremes that can result from blocking events. In this case, the blocking was in a different location than with Sandy and other examples of past extreme events, but it was a factor.

A major question facing climate scientists and meteorologists is whether blocking patterns are becoming more frequent and/or intense, and whether this has to do with Arctic sea ice loss. As you noted, I’ve covered this research before (as recently as last month), and we’re continuing to stay on top of this at Climate Central. Right now, the sea ice melt = more extreme events in northern midlatitudes hypothesis is still just that, a hypothesis, with some studies supporting it and others raising more questions than answers.

In other words, yes, these events in Colorado may possibly be linked tangentially to sea ice loss and related jet stream perturbations, but it’s not an open and shut case. The blocking was far more unusual with Sandy than this event, and the moisture plume from Mexico was arguably a bigger factor in Colorado than anything else.

Reply to this comment

By Jim Steele
on September 14th, 2013

Except for the warm spike during the droughts Boulder’s maximum temperatures are lower than all the 30s See USHCN http://cdiac.ornl.gov/cgi-bin/broker?id=050848&_PROGRAM=prog.gplot_meanclim_mon_yr2012.sas&_SERVICE=default&param=TMAX&minyear=1893&maxyear=2012

To blame CO2 because this is an unusual event shows Freedman’s bias and lack of analysis. Blocking high pressure systems stalled the Low pressure system that drew the Pacific moisture northward and caused that Low to stall and focus the moisture in that location. Blocking highs are most common when the eastern Pacific Ocean is cooler than normal during the Pacific Decadal Oscillations cool phases as is now the case. Climate models underestimate the effects of blocking Scaife, A. A., T. Woollings, J. Knight, G. Martin, and T. Hinton (2010), Atmospheric blocking and mean biases in climate models, J. Clim., 23, 6143–6152

Reply to this comment

By Eric Peterson (Front Royal, VA 22630)
on September 14th, 2013

“In other words, yes, these events in Colorado may possibly be linked tangentially to sea ice loss and related jet stream perturbations, but it’s not an open and shut case. The blocking was far more unusual with Sandy than this event, and the moisture plume from Mexico was arguably a bigger factor in Colorado than anything else.”

There was no blocking in this case, just monsoon moisture.  There are two notable things about this monsoon. FIrst it was not predicted in the seasonal climate models.  Like all models, they are very poor.  Second the monsoon has put a major dent in the extreme areas of drought.  Over the US drought has expanded, but the extreme areas have shrunk.

As it often the case the rainfall does more good than harm, but we will never read about the benefits of flooding since it doesn’t fit the narrative.  In urban areas flooding is indeed problematic but that is mostly because it is an urban area and much of the city of Boulder is flood plain.

Reply to this comment

By Susan Anderson (Boston, MA)
on September 14th, 2013

Excellent article.  Glad to see the increase in blocking events mentioned, and I was also very aware of the serious wildfires last year and wondering how that may have exacerbated the problems.

We will probably not hear quite as much about the events unfolding with Ingrid, but I would suspicion there will be similar problems in Mexico.  Another mention for Greg Laden:

http://scienceblogs.com/gregladen/2013/09/14/ingrid-is-serious-humberto-tries-for-new-record-and-manuel/

Looking on teevee for coverage, I find Al Jazeera is doing a good job as they often do.  Interesting.

Reply to this comment

By Camburn (ND)
on September 15th, 2013

There is strong evidence that the Solar impact on jet stream placement is reflected by the blocking patterns.

To state that this event is tied to Global Warming doesn’t make sense.  The Globe hasn’t warmed for 17-22 years, depending on your temp metric of choice.

We know that the GCM’s do a poor job of reflecting reality and for sure have no predictive abilities as presently written.

To try and make a case that the Colorado rains are a result of Global Warming is a stretch of a broken rubber band.

Reply to this comment

By Clara Chapman (Boulder, CO 80301)
on September 15th, 2013

How’s the weather looking now, Mr. Goddard?

Reply to this comment

By Paulm (Cdn )
on September 15th, 2013

So this is probably how we get carbon draw down from atmosphere. Intense increase in the hydrological cycle, beyond imagination, as the planet warms. We are in for a wild ride starting now.

Reply to this comment

By Eric Peterson (Front Royal, VA 22630)
on September 17th, 2013

” Intense increase in the hydrological cycle, beyond imagination,”

Beyond the imagination of the modelers.  That’s because if they added that to their models, we would end up with negative feedback.  The CO2 warming would be offset by cooling by latent heat transfer.  So instead the climate models that show the world heating up and Greenland melting do not show more storminess, but less.  If they did show more storms, Greenland would not melt.

If we are in for “intense” weather, then global warming is not a problem since weather events like these can be easily mitigated.

Reply to this comment

By John
on September 17th, 2013

If it’s a drought, it’s man made.  If it rains, it’s man made.  If it’s cold, it’s man made.  If it’s hot, it’s man made.  Please!!!!  Give it up already!!!  How about publishing that it’s a proven fact that the extra CO2 in the atmoshpere actually is causing trees to grow quicker, thus replenishing our oxygen by scrubbing out the CO2 all of us horrible humans are producing.  How long has the ice age been gone for?  Um, roughly thousands of years.  How long have humans been using fossil fuels?  NOT thousands of years.  Sorry I don’t have a degree in astrophysics, but DUH…

Reply to this comment

By MB (Erie, CO 80516)
on September 18th, 2013

http://blogs.denverpost.com/library/2012/07/31/big-thompson-flood-disaster-colorado-1976/2795/

This type of event is not without precedent.  How do you distinguish ‘weather’ from ‘climate’? The two may be linked, but establishing causality is a big challenge.  It’s fun to speculate however.

Reply to this comment

By Earthling
on September 18th, 2013

Does anyone seriously believe that extreme weather is any more extreme than it has always been?
Must every extreme weather event be linked to a 0.75º C rise in global temperature over the last 160 years, 0.5 of which allegedly happened in the last 60 years?

Reply to this comment

By Scott Brassfield (Manitou Springs, CO. 80829)
on September 20th, 2013

I have been completely fascinated by burn scar flooding.  Manitou Springs is immediately downstream from Waldo Canyon and Williams Canyon sources of summer 2012 fires that destroyed 245 Colorado Springs homes.  The resultant “burn scars” combine lack of usual plant growth with “hydrophobic” soil.  What makes the soil hydrophobic is that the trees, when they burned, literally exploded spreading sap into surrounding soil and making the soil more impermeable to water.  These factors, combined, make water runoff in these two canyons extremely rapid.  I was able to watch the July 1 and July 19 floods in Manitou Springs out the back window of a bar that over hangs Fountain Creek which receives Waldo and Williams Canyon runoff.  About 15 minutes after strong thunderstorms about a three foot rise in water level roared down Fountain Creek;  and take that word roar literally since we Colorado microbrew drinkers could hear it coming for twenty seconds before it arrived.  And you could tell the source was burn scar runoff because water input from the burn scars was black from forest fire ash, not reddish brown like water from creeks draining unburned forest.

One bit of good news is that recently Williams and Waldo Creeks have returned to being clear after small rains and a sort of dark reddish brown rather than black when it storms and I think they are draining more slowly.  The enormous amount of precipitation, although good for floods, has also been good for plants recently suffering from drought and tree sap mitigation and I believe that runoff from the two canyons is beginning to be a bit more normal.

I believe that Boulder flooding is partly downstream from burned forest possibly called four mile canyon.

Reply to this comment

Name (required):
Email (required):
City/State/Zip:
Enter the word "climate" in the box below:

[+] View our comment guidelines.

Please note: Comment moderation is enabled. Your comment will not appear until reviewed by Climate Central staff. Thank you for your patience.