Researchers find more atmospheric rivers will hit western North America

October 16, 2015
Researchers find more atmospheric rivers will hit western North America
Atmospheric rivers can slam the western USA with heavy precipitation. In this model representation from the Community Atmosphere Model, vertically integrated water vapor is simulated at 30km high resolution. The simulated atmospheric river shows how moisture (dark yellow and orange) is carried from the tropics to the U.S. west coast.

A strikingly large increase in the number of atmospheric river days awaits the U.S. west coast if climate warming remains relatively unchecked. Researchers at Pacific Northwest National Laboratory came to that conclusion after analyzing climate model projections through the end of the century under a comparatively high greenhouse gas emission scenario.

The fractional increase in atmospheric river days falls between 50% and 600%, depending on the seasons and landfall locations. These findings indicate that major challenges lie ahead for those managing water resources and flood risk. That is because atmospheric rivers (see sidebar) often produce heavy, cold season precipitation and flooding when they hit the west coast of North America.

"Atmospheric rivers can bring record-setting precipitation when making landfall in western North America. Our research indicates they will be more frequent under ," said Dr. Yang Gao, a post-doctoral researcher and atmospheric scientist at PNNL, "causing increased flooding events."

On average, atmospheric rivers hit the western United States only a few times each winter, but they transport significant amounts of moisture that converges in the mountains producing heavy precipitation. In a warmer , the atmosphere can hold even more moisture, so it is not surprising that the number of atmospheric river days will increase in the future. However, it is unclear whether some areas will see larger increases in atmospheric river days than others.

This study found that associated with a poleward shift of the subtropical jet in the North Pacific basin, the number of atmospheric river days increases much more significantly in Alaska during spring because both increased moisture and increased wind speed gang up to increase the frequency of atmospheric rivers. These findings provide important insights for future water resource management throughout the North American west coast.

The PNNL research team analyzed model outputs from 24 global climate models used in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). They compared two simulations, present and future, of atmospheric rivers determined from the vertically integrated water vapor flux to quantify the changes in atmospheric rivers that make landfall over western North America. To determine what processes contribute to the changes, they designed a rescaling method to isolate the contributions of changes caused by moisture and those caused by winds. The team found that the increased atmospheric moisture in a warmer climate plays the major role in driving the increases of atmospheric rivers. The changes in winds only slightly pull back the increased atmospheric river occurrences.

"Our study designed a method to quantify factors that contribute to the changes in AR days," said Gao. "It clearly points to the overwhelmingly dominant role of increased atmospheric moisture in a warmer climate that produces the increase of AR days. Even though changes in winds do counter such effect, the effect only moderately limits the large increase of AR events in the future."

Researchers next will analyze the same multi-model ensemble of global climate simulations used in this study to investigate the changes in in the North Atlantic that make landfall in Europe.

Explore further: Atmospheric rivers linked to severe precipitation in Western Europe

More information: Yang Gao et al. Dynamical and thermodynamical modulations on future changes of landfalling atmospheric rivers over western North America, Geophysical Research Letters (2015). DOI: 10.1002/2015GL065435

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Returners
1.4 / 5 (10) Oct 16, 2015
These findings indicate that major challenges lie ahead for those managing water resources and flood risk.


California needs more rain anyway. Over-population and over-irrigation has drained many lakes and aquifers. Unfortunately, subsidence is permanently destroying some of the aquifers.

When's the last time a flash flood obliterated 2000 homes in California?

Well, the wildfires in the west have gotten out of control due to poor management, and they burned over 2000 homes in one event this season.

I think most people might take a little excess water rather than see their home and entire neighborhood burnt to the ground.
krundoloss
1 / 5 (5) Oct 16, 2015
Ha! Say goodbye to your Outdoor living spaces, Californians! And yes they need more fresh water, so overall it could be beneficial. Erosion may be a problem in some areas, too.
antigoracle
2.2 / 5 (10) Oct 16, 2015
Oh GloBULL warming, first you brought us drought and now rain. Is there anything you can't do GloBULL warming...is there anything...
Benni
2.3 / 5 (9) Oct 16, 2015
Does this include the El Nino that has just begun to form in the Pacific that brings more rain to the West Coast? Or is this atmospheric river in addition to that? All my cousins are about to get some relief.
gkam
3 / 5 (10) Oct 16, 2015
"Ha! Say goodbye to your Outdoor living spaces, Californians!"
---------------------------------

Schadenfreude strikes again.
Osiris1
1 / 5 (3) Oct 16, 2015
Mmmmmm....waterrr...love it! Love it! Love it.
plasmasrevenge
2.1 / 5 (7) Oct 16, 2015
Re: "The fractional increase in atmospheric river days falls between 50% and 600%, depending on the seasons and landfall locations."

This 50-600% apparently does not even include the uncertainty of the prediction. The researchers have made it very difficult for me to feel scared. I need solid, round numbers. I'm not sure how to be 50-600% more concerned.
Returners
1.4 / 5 (10) Oct 16, 2015
Re: "The fractional increase in atmospheric river days falls between 50% and 600%, depending on the seasons and landfall locations."

This 50-600% apparently does not even include the uncertainty of the prediction. The researchers have made it very difficult for me to feel scared. I need solid, round numbers. I'm not sure how to be 50-600% more concerned.


I wouldn't worry about it too much. Arc storms happen every couple centuries there anyway, based on geologic evidence.

I am sure the next time one happens it will be labelled "unprecedented" by the weather channel and the twitter zombies, and then blamed on AGW.
SuperThunder
2.1 / 5 (7) Oct 16, 2015
Every time a terrible storm happens now, people die. Tornadoes, death. Flooding, death. Blizzards, death. So don't forget the dead you're stepping over when you say their death's are a conspiracy just to make you and your religio-capitalist masters feel better. Not because I think you are in any way shape or form even biologically capable of the very idea of empathy, but because no one else is ever going to forget that you gladly stepped over the dead to be an idiot, so you'd best remember it too. There's going to be a quiz later.
Bongstar420
1.8 / 5 (5) Oct 16, 2015
But global warming is causing the west to be droughted
gkam
2 / 5 (8) Oct 17, 2015
"But global warming is causing the west to be droughted"
----------------------------------

And the sludge in the bottom of bongs causes mental simplification, usually down to brain stem.
Benni
2.8 / 5 (9) Oct 17, 2015
"But global warming is causing the west to be droughted"
----------------------------------

And the sludge in the bottom of bongs causes mental simplification, usually down to brain stem.


......and why don't you just stop it with the name calling & pig mouth dispersions you & so many others in the Commentary on this site imagine to be such a hallmark of intellectualism.
gkam
2.1 / 5 (7) Oct 17, 2015
But I can solve differential equations!!
jeffensley
1.8 / 5 (5) Oct 17, 2015
Someone tell me what this "information" will do? Do you think California is going to spend $billions in preparations for this potential heavy precipitation? Projections are meaningless until they actually happen. I can plan a week ahead for a day that forecasters say will be sunny, but if it ends up raining that day, am I going to do that outdoor work based on the forecast or based on the reality of it raining?
gkam
1.8 / 5 (5) Oct 17, 2015
It lets us plan for it, so we will not get rained out, or flooded out, or mudslided out, and can save some of the water for later. We will do it individually and in smaller organizations, not necessarily Big Brother.

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