USGS scietists are quietly conducting seminars with local California governments about coming Atmospheric River Storms. One such series of storms in 1861-1862 devestated California, turning the entire central valley into a 30 ft deep inland sea.
Picture the Lake Tahoe basin in a deluge of rain. Weeks of downpouring and melting snowpacks. Landslides render highways and roads impassable. No lights, no water, no heat, no food.
Businesses shut down. The local economy is devastated. And little outside help is on the way, considering outside responders are overwhelmed with storm damage in surrounding areas.
A deluge of this magnitude is inevitable in Lake Tahoe's future, but it doesn't have to turn catastrophic — so long as preventative steps are taken now, two U.S. Geological Survey scientists said during a presentation last Thursday at the Tahoe Environmental Research Center.
Such storms will likely come from atmospheric rivers, gargantuan bands of warm water vapor that form over the Pacific Ocean and move eastward, some of which hold enough water to fill the Mississippi River 10 times over, said Dale Cox, a regional hazards coordinator for the federal agency. Satellite imagery shows them to be at least 1,200 miles long and 250 miles wide.
“Atmospheric rivers are particularly vicious storms,” added Michael Dettinger, a USGS research scientist. “They lift up mountain ranges more easily than other storms, cool, condense out, then boom — lots of rain.”
“You will probably be seeing more atmospheric rivers with climate change,” Cox said. “What you can expect from climate change in the west is expanded periods of drought, higher temperatures, sea level rise and more frequent and ferocious storms.”
An ARkStorm — a hypothetical term developed by USGS that's short for an AR (atmospheric river) 1000 (k) storm — is an extreme scenario featuring continual downpour of two to eight inches of rain a day for extended periods in California.
The last catastrophic series of rain storms hit California in 1861-62, causing extensive flooding across the state, devastating the economy. According to various historical accounts, newly elected California Gov. Leland Stanford had to be taken to his inauguration in a rowboat.
Cox said current AR 1000 scenario models (Disaster preparedness drills) are scaled back from the 1861-62 storms.
“If people see a possible catastrophic event as being too large, they think it is not believable and they don't prepare for it,” he said.
Dettinger said he and Cox came to Tahoe last Thursday and presented at TERC “to discuss who from the area we should connect with so that such an effort was of maximum utility for emergency responders, planners and the community at large.”http://www.tahoebonanza.com/article/20130205/NEWS/130209988/1001&parentprofile=1485
Geologic evidence shows that truly massive floods, caused by rainfall alone, have occurred in California every 100 to 200 years. Such floods are likely caused by atmospheric rivers: narrow bands of water vapor about a mile above the ocean that extend for thousands of kilometers.
The atmospheric river storms featured in a January 2013 article in Scientific American that I co-wrote with Michael Dettinger, The Coming Megafloods, are responsible for most of the largest historical floods in many western states. The only megaflood to strike the American West in recent history occurred during the winter of 1861-62. California bore the brunt of the damage. This disaster turned enormous regions of the state into inland seas for months, and took thousands of human lives. The costs were devastating: one quarter of California’s economy was destroyed, forcing the state into bankruptcy.
A January 15, 1862, report from the Nelson Point Correspondence described the scene: “On Friday last, we were visited by the most destructive and devastating flood that has ever been the lot of ‘white’ men to see in this part of the country. Feather River reached the height of 9 feet more than was ever known by the ‘oldest inhabitant,’ carrying away bridges, camps, stores, saloon, restaurant, and much real-estate.” Drowning deaths occurred every day on the Feather, Yuba and American rivers. In one tragic account, an entire settlement of Chinese miners was drowned by floods on the Yuba River.
This enormous pulse of water from the rain flowed down the slopes and across the landscape, overwhelming streams and rivers, creating a huge inland sea in California’s enormous Central Valley—a region at least 300 miles long and 20 miles wide. Water covered farmlands and towns, drowning people, horses and cattle, and washing away houses, buildings, barns, fences and bridges. The water reached depths up to 30 feet, completely submerging telegraph poles that had just been installed between San Francisco and New York, causing transportation and communications to completely break down over much of the state for a month. William Brewer wrote a series of letters to his brother on the east coast describing the surreal scenes of tragedy that he witnessed during his travels in the region that winter and spring. In a description dated January 31, 1862, Brewer wrote:
Thousands of farms are entirely under water—cattle starving and drowning. All the roads in the middle of the state are impassable; so all mails are cut off. The telegraph also does not work clear through. In the Sacramento Valley for some distance the tops of the poles are under water. The entire valley was a lake extending from the mountains on one side to the coast range hills on the other. Steamers ran back over the ranches fourteen miles from the river, carrying stock, etc, to the hills. Nearly every house and farm over this immense region is gone. America has never before seen such desolation by flood as this has been, and seldom has the Old World seen the like.http://www.scientificamerican.com/article.cfm?id=atmospheric-rivers-california-megaflood-lessons-from-forgotten-catastrophe
But what's not such a good thing is that every once in a while these atmospheric rivers, which are like a fire hose that kind of snakes around, it becomes stationary and it just blasts California with what we call a megaflood. These events have happened historically. In fact, there was a huge megaflood in 1861-1862, 43 days of rain that flooded the entire Central Valley in California. It killed thousands of people. The concern is that it's due to happen again.
Here's the connection with climate change: more water vapor in the atmosphere (about 4 percent increase) may make these storms a little more frequent. We're due for another one. The concern is this could happen in the near future in California.
They are sort of rivers in the atmosphere. The jet stream is the river of air in the atmosphere, we use that analogy, that guides storms. The jet stream focuses these moisture plumes so it really is sort of an atmospheric river. These are the things that occasionally spray California with these heavy rainfalls. The concern here with this sort of nightmare scenario, what they call California's other big one, is that one of these will happen again and there's historical precedent that it's happened in the past.
In fact one of the big megastorms we had a couple of winters ago was a remnant of one of these atmospheric rivers. The climate change component is that the severity and the frequency of these could increase. If one of these occurred today, they're talking about six million people in the path in California. Remember in that 1861-1862 event, Sacramento was under 10 feet of water. The whole Central Valley turned into an inland lake that was something like 300 miles long and 20 miles wide. So this kind of an event, when it occurs, could make Sandy or Katrina look like a walk in the park.
If you took all the water vapor that's being conducted along these atmospheric rivers and condensed it into liquid water, it would be the same as essentially seven to 15 Mississippis worth of water. Whether you believe in climate change or not, we know from sediments on the ground that in California and frankly up and down the west coast that there are storms out there that happened in the past. They're natural occurrences, they happen about every couple hundred years and we frankly should expect them to happen again.
We've talked about the documented increase in excessive rainfall events in the Midwest and Northeast. This is another angle on that. Yes, they've been naturally occurring events in the past, but the infrastructure of California has changed completely since the last time one of these events occurred. Climate change does make the extremes more extreme. It does produce more of these extreme rainfall events and if something on this scale happens in the state of California, the economic catastrophe we're talking about, maybe 25 percent of all buildings damaged.
The advent of satellites since the '60s and '70s has really opened a whole new world of research and really opened our eyes to be able to see these things. So you can actually see these plumes as they move throughout the Pacific and make their way into the west coast of the United States. That technology has increased greatly in the last 20 or 30 years.http://minnesota.publicradio.org/display/web/2013/02/05/daily-circuit-climate-cast?refid=0