Ocean conditions likely to reduce Colorado River flows during this winter's drought

Oct 01, 2010 By Meg Sullivan

(PhysOrg.com) -- The convergence in the coming year of three cyclical conditions affecting ocean temperatures and weather is likely to create unprecedented challenges for states that depend on water from the Colorado River, a new UCLA study suggests.

The convergence in the coming year of three cyclical conditions affecting and weather is likely to create unprecedented challenges for states that depend on water from the Colorado River, a new UCLA study suggests.

"If I were concocting a recipe for a perfect drought, this would be it," said Glen MacDonald, co-author of the study and director of UCLA's Institute of the Environment and Sustainability.

Along with a former graduate student, MacDonald has found that the combination of La Niña with two less commonly known ocean conditions — the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation — tends to result in drought in the upper reaches of the Colorado River. The ocean conditions have been known to diminish precipitation in the Southwest but, examined separately, have proven to be poor indicators of in the upper reaches of the river.

"It's the combination that's key," said lead author Abbie Tingstad, who conducted the research as a graduate student in geography at UCLA. She is now an associate physical scientist at the RAND Corp.

The convergence of these patterns in the Pacific and Atlantic oceans may well drive water levels in the Lake Mead reservoir below a critical threshold and could potentially result in reduced water allocations for Arizona and Nevada, the researchers say.

Essentially all of the Colorado River water used by Southern California passes through the reservoir, which is the largest in the nation. Fed primarily by snowpack melt from its upper reaches, the river is Southern California's chief source of water.

"Declines in water availability of this magnitude during the coming winter could be devastating for states that depend on the Colorado River for their water," Tingstad said.

The study appears in the October issue of the Journal of the American Water Resources Association.

By studying ancient tree rings, Tingstad and MacDonald were able to reconstruct river flow and winter snowpack levels going back several hundred to almost 1,000 years for a mountainous region of northeastern Utah. Responsible for 10 percent to 15 percent of the flow in the river, the Uinta Mountains region has a climate representative of the upper Colorado River basin, the researchers say, so conditions experienced there are similar to those that occurred elsewhere in the upper basin.

The tree rings came from a combination of dead and living pinyon pines that grow on extremely dry slopes in the Uintas. Described by Tingstad as "listening posts for climate variability and drought," the trees produce annual rings that are so sensitive to water stress that the researchers can track changes in annual precipitation on the order of an inch by studying them under microscopes.

Tingstad and MacDonald then compared their records with existing records for La Niña, the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). During a La Niña episode, the sea-surface temperature across the Pacific Ocean at the equator plummets by as much 18 degrees Fahrenheit, resulting in drops in precipitation rates of as much as 50 percent across the southwestern and southeastern United States for between five and 18 months.

The PDO is a pattern of climate variability with longer-term shifts that last between 20 and 30 years and also affect weather. A negative PDO is characterized by cooler sea-surface temperatures off the Pacific Coast of North America that can result in below-average precipitation in the southwestern U.S. The effect can be thought of as an extended La Niña event.

Each phase of the AMO can last for more than 60 years and is characterized by temperature changes in the North Atlantic Ocean. In its positive phase, the AMO has little impact on California weather if it occurs in absence of a negative PDO. But the positive AMO has been linked to past occurrence of major droughts in the Midwest and the Southwest, including the Dust Bowl of the 1930s.

"It's three different things working on different times scales," MacDonald said. "You may not get them to line up that frequently."

Tingstad and MacDonald found a "striking and significant propensity" for droughts in northeastern Utah when cool sea-surface temperatures in the Pacific associated with La Niña and the negative phase of the PDO were coupled with warm temperatures in the North Atlantic linked to the positive phase of the AMO. During such episodes, snowpack declined on average between 9 percent and 10 percent, and river discharge decreased on average by 18 percent.

The three conditions last converged at least five times between 1945 and 1965, a period that was characterized by generally depressed but variable flows in the river, they said.

The findings are troublesome because not only are all three conditions predicted for 2010-11, but they are expected to be particularly strong, the researchers say. The coming year's La Niña and AMO are at this point supposed to be the strongest in 10 years, and a strong negative PDO is also building.

The convergence increases the likelihood that Lake Mead, already diminished by 11 years of drought, will fall below 1,075 feet above sea level — a threshold that can result in the reduction of water allocations in Nevada and Arizona, the researchers say. Under a series of agreements among seven U.S. states along the Colorado River and Mexico, California has first rights to the water, so it would not face the same restrictions. Water levels at Lake Mead currently stand just nine feet from the critical threshold, at 1,084 feet above sea level.

"We're looking at a situation that could pit us against our neighbors," said MacDonald, who is also a UCLA professor of geography. "We've never had to face such a severe decline in Lake Mead and resulting reductions in Colorado River allocations before."

Under the agreements, the federal authorities have the power, once Lake Mead falls to 1,075 feet, to request reductions of 11.4 percent on Arizona and 4.3 percent on Nevada — cuts of 320,000 and 13,000 acre feet, respectively.

"That means these states might have to find many millions of gallons to make up what seem like relatively small-percentage reductions, and they have to do so at a time when they are already in a drought of considerable duration," MacDonald said. "That's going to be a real problem."

Explore further: Evolving plumbing system beneath Greenland slows ice sheet as summer progresses

Related Stories

Pacific chills with growing La Nina

Sep 16, 2010

(PhysOrg.com) -- The tropical Pacific Ocean has transitioned from last winter's El Nino conditions to a cool La Nina, as shown by new data about sea surface heights, collected by the U.S-French Ocean Surface ...

Oscillation Rules as the Pacific Cools

Dec 10, 2008

(PhysOrg.com) -- The latest image of sea-surface height measurements from the U.S./French Jason-1 oceanography satellite shows the Pacific Ocean remains locked in a strong, cool phase of the Pacific Decadal ...

Water supply shifts as global climate changes

Jun 15, 2009

Many of the world's great rivers are becoming less so. Yet in the Midwest, the wet is getting wetter. So says a study that finds global climate change shifting weather and water patterns around the planet.

Adios El Nino, Hello La Nina?

Jun 22, 2010

(PhysOrg.com) -- The moderate El Nino of the past year has officially bowed out, leaving his cool sister, La Nina, poised to potentially take the equatorial stage.

Recommended for you

Sculpting tropical peaks

7 hours ago

Tropical mountain ranges erode quickly, as heavy year-round rains feed raging rivers and trigger huge, fast-moving landslides. Rapid erosion produces rugged terrain, with steep rivers running through deep ...

Volcano expert comments on Japan eruption

8 hours ago

Loÿc Vanderkluysen, PhD, who recently joined Drexel as an assistant professor in Department of Biodiversity, Earth and Environmental Science in the College of Arts and Sciences, returned Friday from fieldwork ...

NASA's HS3 looks Hurricane Edouard in the eye

21 hours ago

NASA and NOAA scientists participating in NASA's Hurricane and Severe Storms Sentinel (HS3) mission used their expert skills, combined with a bit of serendipity on Sept. 17, 2014, to guide the remotely piloted ...

User comments : 6

Adjust slider to filter visible comments by rank

Display comments: newest first

Quantum_Conundrum
3 / 5 (4) Oct 01, 2010
Hey idjits, MAKE DESALINIZATION PLANTS IN CALIFORNIA AND PUMP THE WATER TO WHERE IT'S NEEDED.

Desalinization should become the PRIMARY source of drinking water, so that desertification of the regions surrounding man-made dry creek and lake beds can be reversed.
Jonseer
4.2 / 5 (6) Oct 01, 2010
NV AZ UT CO do NOT have ocean access, so what water can they desalinate?

Even if they had access, who would pay for those desalinization plants?

NONE of the Co. River basin states would approve the truly massive increase in taxes necessary to pay for a desalinization plants (THEY ARE EXPENSIVE TO BUILD , RUN N MAINTAIN).

Oh I know Private Business, right. They'll build if they can be assured of a 150% return, which would mean few people would be able to afford their water.

OH I GET IT. Let the Federal Gubment pay for it?

After years of those states bitchin' about Fed. control - I don't think so.

A better idea would be cancel up outdated water rights with built in inefficiencies in a state of emergency,

Put all irrigation canals under roofs or underground.

ELIMINATE WATER THIRSTY CROPS. Arizona has NO business growing cotton in the desert Etc.

No more water thirsty golf courses in Vegas.

Mining Cos. should be mandated to recycle all water.

Far better, cheaper and doable!
mertzj
3 / 5 (2) Oct 02, 2010
If california can get that much water from lake mead... im guessing those same pipeline could be reversed? actually im not even guessing... now if those fellas up at livermore could hurry up fusion a little bit there wont be a problem. But i definitely agree farmers in az should probably consider relocating.
Jonseer
3 / 5 (2) Oct 02, 2010
Mertz why do you think AZ and NV have the right to CO river water over NV and AZ.?

If it's because their further upstream, then does that mean Utah can take it all?

AZ. keeps its salt river and gila river water to itself, on top of its CO allotment.

Of course, virtually the entire flow of water in the CO river comes from rain and snow pack in Colorado. So does that mean Colorado can take it all?

Mertzi California has legal claim too the water.

It was a state 60 years on when Az became a state.

NV has the smallest border of all Colorado River states.

So why do you hate California so much?

Why do you think it's right to break the laws. Steal Ca. legal water, and give it to even drier states that waste water like there is no tomorrow.

Ca. is not perfect, but when it comes to common sense with water it makes NV and AZ look like careless fools.
Quantum_Conundrum
1 / 5 (2) Oct 03, 2010
Jonseer:

You weren't paying attention were you?

Make Desal plants for california.

If people keep draining the lakes and river basins in the SW U.S. the entire western side of the country is going to become a desert, as is already happening in many locations where people have totally drained lakes and rivers for drinking water.

You just THINK there's ecological problems right now. Wait till all the grass lands and forests around these regions dies out from man-made desertification.
Skeptic_Heretic
3 / 5 (2) Oct 03, 2010
If california can get that much water from lake mead... im guessing those same pipeline could be reversed? actually im not even guessing... now if those fellas up at livermore could hurry up fusion a little bit there wont be a problem. But i definitely agree farmers in az should probably consider relocating.

Problem is, water runs downhill, not uphill.
If people keep draining the lakes and river basins in the SW U.S. the entire western side of the country is going to become a desert,
You mean return to being a desert. California had great soil, and no water when we first made our way out there. We brought the water into the region and created the farmland. It's entirely unnatural in origin. Northern cali was scrubland and forrest. Southern was almost purely desert and scrubland.