For the past five years, as drought sucked dry California’s water sources and depleted its reservoirs, Southern California water managers have turned increasingly to the region’s large out-of-state water source: the Colorado River.

Now, Orange County, which draws up to half its annual supply from the river that snakes from the Rocky Mountains to Mexico, and other thirsty coastal communities are facing increased competition for reduced flows from the drought-strangled Colorado.

Experts warn that if water availability and demand aren’t balanced through conservation, recycling plants and water desalination facilities costing billions of dollars, everybody’s cut of the river will shrink and consumers’ water rates will inevitably rise.

“Shortages are coming. It’s really not a question of if, but when,” said Bill Hasencamp, the manager of Colorado River Resources at the Metropolitan Water District, which manages and sells imported water to Orange, Los Angeles and San Diego counties. “Is there a way to collectively live within our lower needs?”

LION’S SHARE OF SUPPLY

The lifeblood of the Southwest, the Colorado is the most litigated and politically contentious river in the country. It supplies water to seven states and Mexico.

The river starts high in Colorado’s Rocky Mountains as melting snowpack. It wends out of the mountains and is joined by tributaries originating in Wyoming and New Mexico. It drops through dusty southern Utah and the canyons of northern Arizona, past the neon lights of Las Vegas and Hoover Dam at Lake Mead. In Mexico, it dries to a trickle beyond Morelos Dam before reaching the Gulf of California.

Toward the end of the river’s run, along the Arizona-California border, a 242-mile aqueduct with two reservoirs and five pumping stations diverts water to the Coachella and Imperial Valleys, Orange County and elsewhere in Southern California.

On a hill above Yorba Linda, at the Robert B. Diemer Treatment Plant, imports from the Colorado River and Northern California are blended and treated, then piped to hundreds of thousands of homes and businesses. In years such as 2014, when northern supplies are cut back and the State Water Project delivers as little as 5 percent of requested water, the Colorado River makes up the lion’s share of the local blend.

Between the 1940s and 1990s, plentiful Colorado River water allowed Southern California to boom. Today, a host of problems call into question whether Orange County can continue to rely on the river’s flow. Climate change is likely to constrict it and political factions continue to squabble over how to divide an ever-shrinking flow.

“There are a lot of pipes that draw from it, and we’re toward the end of the line,” said Garry Brown, the executive director of Orange County Coastkeeper, a local environmental group. “We have legal rights to the water we take from the river, but for us to say it’s always going to be there and we’re always going to be able to draw water from it is foolhardy.”

Brown is optimistic that local investment in conservation and recycling can ensure an adequate Orange County water supply for the future. In the past year, Orange County cut water use 25 percent. And the Orange County Water District is planning to build additional capacity at its Fountain Valley recycling plant.

At the same time, virtually all of south Orange County’s water has come from the Colorado River in recent years, noted Dan Ferons, the general manager at Santa Margarita Water District.

To ensure reliable delivery of water in the face of lower rainfall across the West and the possibility of reduced imported supplies, water managers in those areas are seeking new sources, increasing local reservoir capacity in Santa Margarita Water District and storing water in the small San Juan groundwater basin.

Metropolitan Water District, the water wholesaler that manages Southern California’s imported water supplies, is also pursuing new water sources, including a recycling plant in Carson that will deliver some water to Orange County, along with agreements to get water from farmers who fallow their fields.

Each new source increases costs for ratepayers. Ferons projects that rates for his customers will rise about 50 percent in the next decade. “The next drop of water is always going to be more expensive than the current drop of water,” he said.

‘SHORTAGES ARE COMING’

On the Colorado River, water supplies are already squeezed.

For 16 years, drought has wracked the river system. Water managers forecast an 18 percent chance a shortage will be declared in 2017, which will yank back supplies for Arizona and Nevada. Those odds rise to 52 percent in 2018 and even higher for 2019.

California is unlikely to keep its first-in-line position for Colorado River water, experts say, because it’s politically untenable to cut other states’ allocations to near-zero while leaving California untouched.

As politicians and bureaucrats quarrel over the division of the river’s flow, the Colorado has little, if any, more to give. Most years, the river never makes it to the Sea of Cortez. Humans plunder all of it – their demand outstripping what nature can offer – and the river simply can’t sate the appetites of the farmers, golf courses and tract homes that rely on it.

In 2000, because of several wet years, Lake Mead was essentially full. Now, bone–white, sun-bleached cliff sides loom over the reservoir and exposed rings show the water level has plummeted 12 stories.

Even in years of average snowfall, Lake Mead will continue to empty because, in 1922, the seven states that use its water allotted themselves more water than comes down the river in a typical year.

At the time, water negotiators assumed that about 16.5 million acre-feet would be available annually. They gave 7.5 million acre-feet to the Upper Basin states – Colorado, Wyoming, Utah and New Mexico – and another 7.5 million acre-feet to the Lower Basin states – California, Arizona and Nevada. Later, in 1944, they added 1.5 million acre-feet of water for Mexico into the agreement.

The problem was the decades prior to 1922 “happened to be the wettest period in the last 500 years, by quite a bit. It was an outlier,” said David Meko, a professor at the University of Arizona, who has done historical reconstructions of Colorado River flows using tree-ring data. “They couldn’t have picked a worse time for allocating the water.”

Modern estimates peg the river’s flow at about 14.9 million acre-feet, or about 1.5 million acre-feet of water less than currently promised.

There are other losses the 1920s water managers failed to account for, such as evaporation at Lake Mead, moisture sucked up by plants along the river and seepage into the ground.

OVER-ALLOCATED

For decades, not all the states took their full share, so the over-allocation of the river didn’t pose a problem. California, which is allocated 4.4 million acre-feet, was able to take 5.2 million acre-feet. That changed in the late 1990s when population growth caused Nevada and Arizona to demand their full allocations, and Arizona began storing some of its excess water in the ground.

In 2003, an agreement slashed California’s water supply. Metropolitan Water District, which had been using water unclaimed by others, took the brunt of the hit.

So the urban water agency ramped up water transfer agreements, paying agricultural districts money to fallow fields or install more efficient irrigation equipment in exchange for water.

“When you have a lot of water and people need water, you become the obvious solution to their problems,” said Tina Shields, the Colorado River resources manager at Imperial Irrigation District, an agricultural district.

In coming years, farms and cities alike will have to grapple with further squeezes on water supply caused by climate change.

As the West’s mountains warm, experts predict snowpack will melt earlier in the spring and surge into reservoirs, where water evaporates more quickly. Higher temperatures also raise the atmosphere’s capacity to absorb moisture, meaning that more moisture is drawn out of soil, plants, rivers and reservoirs.

All told, scientists predict a 3 to 4 percent drop in runoff per degree of warming, said Jeff Lukas, a researcher at the Western Water Assessment, a federal partnership with the University of Colorado, Boulder. So, if the planet warms by 4 degrees by 2050, what many scientists consider a conservative estimate, runoff in the Colorado River could decrease as much as 15 percent.

“That puts us in a state of chronic to moderate drought relative to historic conditions,” Lukas said.

There’s a chance climate change could bring more precipitation to the Colorado River basin – which would offset the reduced runoff caused by the higher temperatures. But most climate forecasts project a total decrease in runoff to the river, said Lukas.

Additionally, scientists have observed more dust blowing from the deserts of Utah to the Colorado mountains, discoloring the snowpack.

“You’re taking a light surface and you’re making it darker,” said Jason Neff, a University of Colorado, Boulder geological sciences associate professor. “Dark surfaces absorb the light and turn it into heat. It will accelerate the melt of the snowpack” and evaporation downstream.

Climate change also is likely to dry out deserts even more, which will increase the amount of dust blanketing parts of the snowpack, scientists say. But they aren’t sure when that is likely to occur or how a hotter, drier climate ultimately would affect Colorado River flows. That’s partly because they have only 50 years of good data on the river.

Gus Goodbody, a water supply forecaster for the Colorado River at the National Water and Climate Center, said: “The reality is, we haven’t been here long enough to understand how the fluctuations naturally occur here.”

Contact the writer: aorlowski@ocregister.com. Twitter: @aaronorlowski