Craig Miller

Watering fields in the Sacramento Valley: traditional irrigation methods have required a lot of guess-work.

By Vinnee Tong

Near the Central Valley town of Los Banos, Anthony Pereira opens a tap to send water into the fields at his family’s farm. Pereira grows cotton, alfalfa and tomatoes. And he is constantly deciding how much water is the right amount to use.

“Water savings is always an issue,” he says. “That’s why we’re going drip here on this ranch. We gotta try to save what we can now for the years to come.”

Thanks to some new technology, that might get a little easier. To help farmers like Pereira, engineers at NASA and CSU Monterey Bay are developing an online tool that can estimate how much water a field might need. Here’s how it works: satellites orbiting the earth take high-resolution pictures — so detailed that you can zoom in to a quarter of an acre.

“The satellite data is allowing us to get a measurement of how the crop is developing,” says CSUMB scientist Forrest Melton, the lead researcher on the project. “We’re actually measuring the fraction of the field that’s covered by green, growing vegetation.”

Those images are combined with data they’re collecting right now at a dozen California farms from Redding to Bakersfield and from Salinas to Visalia.

In Pereira’s fields a tractor carrying tomato seedlings leads the way as farm workers nestle the plants into the dirt. Alongside them the researchers drill holes in the ground to put sensors underneath and around the crops. The sensors measure wind temperature, radiant energy from the sun and how thirsty the soil may be on a given day.

Walking through the field, researcher Chris Lund is carrying equipment that will collect all that data.

“Once a minute it’ll take a measurement of all the sensors that are attached to this,” he explains, “the soil moisture sensors, the soil water potential sensors, and in this case the capillary lysimeter, which measures how much water is going out the bottom of the system.”

Using this information with the satellite images that are updated about once a week, the researchers have come up with a formula that can estimate how much water a field might need. Farmers will soon be able to access estimates for their fields online and eventually they’ll be able to use their cell phones.

That means Pereira will no longer have to rely on the old-school way of deciding how much water to use.

“Before, everything was furrow-irrigated or flood-irrigated, and we’d just schedule depending on what the weather is,” he told me. “If it’s warm, we say, ‘OK we’re going to try to irrigate every two weeks.’ If it’s cooler, then let’s try to stretch it out another week, 10 days or so to make the water stretch out more.”

The California Department of Water Resources estimates water savings could amount to hundreds of dollars per acre, and the crop yield could be better, too. The joint research team sees its water-saving tool as something that could be used by any farmer. At the Ames Research Center in Mountain View, NASA’s Rama Nemani studies a map of the world mounted on a wall.

“If you look at the map like this, there are a lot of areas that are like California that are starved for water but need to still produce food,” he says. “So we have to figure out how to use whatever limited water each place has to the best possible extent.”

This online water saving tool could be available at no cost to farmers around the state as soon as next year, and eventually to farmers around the world.

Hear the radio version of this story from KQED’s The California Report.

How many gallons to run that microwave?

Lauren Sommer / KQED

A natural gas power plant in Long Beach that uses "once-through" cooling.

We hear a lot about how green our energy is in California. Instead of using coal, the state runs on natural gas and increasingly, renewable power.

But there’s a hidden cost to our energy supply: water use. In fact, every time you turn on a light, it’s like turning on your faucet. It’s been calculated that it takes 1.5 gallons of water to run a 100-watt light bulb for 10 hours.

The way water and power work together is a lot like a tea kettle. Steam drives the power industry.

How Power Needs Water

You can see it at the Gateway Generating Station, a natural gas power plant in the northeast Bay Area. The plant looks complicated but making power is pretty simple. Step number one: burn natural gas. That produces a lot of heat.

“You’ve got 1,700-degree exhaust energy, or waste heat,” says Steve Royall of PG&E, who is giving me a tour through the maze of pipes and compartments. The heat hits pipes that are filled with water and the water is boiled off to create steam. That’s step number two: make steam to turn a steam turbine, which is attached to a generator. It’s the water that’s making the power.

Source: National Renewable Energy Laboratory. Illustration by Andy Warner.

But water has another job in power plants. That steam, even after it makes power, is still hot. So, most power plants use water to cool it down. “You’ve got to have the ability to cool everything down so the cycle can continue and your equipment doesn’t overheat,” says Royall. (Learn more about how power needs water in this illustration).

Nuclear plants and coals plants use water the same way, in some cases, millions of gallons a year. In fact, nationwide, power plants need more freshwater than farms do, according to a U.S. Geological Survey study.

Newer power plants reuse water, but a lot of it is lost to evaporation, which means it has to be replenished. “Typically water has been the most abundant resource available,” says Royall, “but as water resources become more valuable, it’s extremely important that we think about water use.”

Future of Water Scarcity

“There is a general understanding that the era of abundance is over,” agrees Heather Cooley of the Pacific Institute, an Oakland-based think tank focused on water issues.

“Water resources are limited and there is a growing demand. We have growing population in the West. We have a growing economy.”

And then there’s the climate – which is changing. “The climate models suggest that water availability will be more variable. So we’ll have wetter years, we’ll have drier years. We’ll have a smaller snowpack,” says Cooley. In some places, power plants are already feeling the effects of tightening water supplies.

Power plants can cut their water impact by using recycled water. “We can look at less water-intensive renewable energy systems. So looking at wind and at solar panels,” says Cooley.

But it turns out, some renewables need water, too.

Solar Technology Grapples with Water Costs

In a parched corner of California’s Mojave Desert, construction equipment shimmers in the mid-day heat. These 3,500 acres near the Nevada border are the site of the Ivanpah Solar Project.

“The Ivanpah project, when it’s operational, will be the largest solar thermal project operating in the world,” says Joseph Desmond with BrightSource Energy.

You’ll notice he said “solar thermal,” a technology that’s different than the solar panels you see on rooftops. The plant is a huge field of mirrors that are specially angled to focus the sun’s heat at a tower, 400 feet tall.

“Inside the top of that tower is a boiler. All of the energy is then is used to create high temperature, high pressure steam in excess of 1,000 degrees Fahrenheit,” says Desmond.

That spins a steam turbine that makes electricity. Just like a natural gas plant, that steam has to be cooled back down, which is normally done with water. In the desert, it’s not easy to find. “You have to dig down, I want to say about 840 feet,” says Desmond.

The Ivanpah solar project under construction. (Photo: BrightSource Energy)

So, the Ivanpah plant will use a new technology called “dry cooling.” Instead of using water, the plant uses massive fans to blow air over the pipes of hot steam. “Air cooling allows us to reduce the water consumption by as much as 90%,” says Desmond.

But there’s a catch. Dry cooling uses more energy, so the plant’s not as efficient. It’s even less efficient when it’s hot out.

It also costs more to build. “It can range between one and five percent more. Now, that may not seem like a lot but when you’re competing and every penny counts, it’s an important factor,” Desmond says.

Three of the seven solar thermal plants planned in California won’t use dry cooling. But Desmond says, even though the state needs renewable power, he doesn’t think agencies would approve that today. “I think it’s safe to say if somebody said we’d like to use water cooling, that getting a permit for that would be challenging to say the least.”

The same could be true for fossil fuel plants, too, as California’s future water supply is called into question more and more.

Explore the Water and Power series and hear Lauren’s radio story on KQED’s The California Report.

NASA

This image shows La Niña conditions from last month, collected by NASA's Jason-2 satellite.

This has been a historically dry winter, dry enough that it’s likely to land a spot as one of the top ten driest since the Gold Rush. And even though La Niña is waning, that probably won’t make much of a difference, because there’s a delay between when ocean surface temperatures change, and when that change actually has an effect on our weather.

“March 20 is just around the corner, and that’s the first day of spring. Our winter — our snowpack and our rain — is essentially over,” NASA Jet Propulsion Laboratory climatologist Bill Patzert told me. Though Patzert’s observation comes as three Pacific storms are poised to potentially bring a week of rain to Northern California, he said, “a weakening La Niña won’t necessarily give us a March miracle in terms of snowpack and rainfall.”

La Niña is caused by colder-than-average ocean surface temperatures in the equatorial Pacific. It typically makes for warm, dry winters in California. But not always. Last year was also affected by La Niña, and it was historically wet.

“I find that as a great teaching moment,” adds Jan Null, from Golden Gate Weather Services. “We look at 20 La Niña years since 1950, and you come up with the average conditions. Well, those averages are made up of a wide range and we’ve seen both ends of that range in the past two years.”

Or, as Jim Mathews, lead forecaster at the National Weather Service Forecast Office in Sacramento put it with a laugh, “Normal here in California is the average of two extremes. It seems to be wet and dry and then we take an average and call that normal.”

Craig Miller

Frank Gehrke conducts a manual snow survey using a "Mt. Rose gauge," essentially a hollow aluminum tube shoved into the snow at predetermined locations.

In California, where most of our water comes from the mountains, being able to accurately measure the snow pack is vital. And it is in outlier years like this — very dry years, though the same goes for very wet ones — when water managers have the hardest time making accurate predictions.

“Knowing the water content of the snow in an entire watershed is the holy grail for snow scientists,” survey guru Frank Gehrke told me.

During the winter, Gehrke trudges into the woods on a monthly basis to do manual snow surveys for the state Department of Water Resources. DWR uses remote snow sensors, too. But even with all that data we don’t get an exact picture of the snow pack. So scientists from National Center for Atmospheric Research (NCAR) and NASA Jet Propulsion Laboratory (JPL) are developing tools to measure snow with lasers. This new technology has the potential to be that holy grail that Gehrke’s looking for.

At NCAR, scientist Ethan Gutmann is working on a stationary laser instrument. His prototype in the Rocky Mountains is installed on a pole in a snowfield. It sends out light pulses, which bounce off the snow and back to the instrument, which then measures the depth of the snow based on the time it takes for the light to come back. The tool isn’t measuring snow on a watershed-scale yet, but Gutmann says that’s a matter of cost, not of technology.

Ethan Gutmann, NCAR

Gutmann's laser tool reveals the features of a snow field above the treeline of a mountain in Colorado.

“The laser system is expensive, but easy to use,” he told me. He’s hoping as the technology improves, these kinds of tools will become more affordable; water agencies will be able to install the stationary instrument in snow fields and get results in real time.

Here in California, DWR is working with JPL on developing the technology to measure snow with lasers from airplanes. These airborne surveys don’t provide the accuracy and continuous data that the stationary tool provides, but they will be able to measure a much larger area. There’s preliminary work now on the Upper Tuolumne River Watershed, which feeds the Hetch Hetchy reservoir. Gehrke says the need baseline measurements without snow, so they’re planning prototype flights in late-July, then plan to fly over the snow beginning in 2013.

There are drawbacks to lasers. They can’t see through most trees, so the technology is most effective above the treeline (the highest elevation where large trees grow). And lasers can only measure the depth, not the water content, of snow. Gutmann said that’s not a deal-breaker, since depth measurements will be so much more accurate than they are now, over a larger area. The key for Gehrke will be combining the technologies. He told me the stationary and airborne lasers complement each other, and when combined with the tools he’s already using, he’ll get a better picture of the snow pack than ever before.

Roguephotonic/Flickr

By Lance Williams, California Watch

Post Peak Pass is a granite notch on the remote southern boundary of Yosemite National Park, altitude 10,700 feet.

On Saturday, its north face was partly covered with a 100-yard-long patch of crusted snow – a reminder of just how emphatically California’s three-year drought was broken by the wild winter of 2010-11.

Although California’s high peaks still are capped with last year’s snowpack and its reservoirs are brimming with runoff [PDF], voters will be asked next year to approve an $11.1 billion state water bond measure that was crafted in response to the crippling drought.

But with the drought a fading memory and the state’s finances in disarray, many believe the pricey package of dam-building and water conservation infrastructure has an even slimmer chance of passage today than in 2010, when then-Gov. Arnold Schwarzenegger yanked it off the ballot and slated it instead for November 2012.

Gov. Jerry Brown has indicated he thinks the water bond as written – its centerpiece is a proposed massive new dam on the San Joaquin River east of Fresno – is too expensive. State Senate leader Darrell Steinberg, D-Sacramento, who helped negotiate the legislative compromise that led to the original measure, agrees it should be scaled back because of state financial issues, said spokeswoman Alicia Trost.

The agreement that undergirds the ballot measure was significant, she said, because it committed the state to tough water conservation policies.

“The other part is financing to meet our water needs,” she said. “They don’t go away because we have good policy behind it.”

Lawmakers have until next summer to decide what to do: In theory, they could revise the bond measure, kill it outright or leave it on the ballot as written.

But revising the measure is no simple task, because any change – even another postponement of the vote – must be approved by a two-thirds vote of the Legislature.

When it comes to revising the water bond, “everything is challenging,” said Bruce Reznik, executive director of the Planning and Conservation League, which objects to the measure’s emphasis on building new dams.

“Nobody thinks it’s got a snowball’s chance of passing” as written, Reznik said. But it’s “an uphill battle” to rewrite the measure, he said, because of the two-thirds vote requirement.

Complicating matters further, many of the parties to the original compromise are no longer on the scene, said another critic, Jim Metropulos of the Sierra Club.

“This was decided by a different Legislature and a different governor,” he said.

State Department of Water ResourcesMark Cowin, director of the California Department of Water Resources

The politics are different as well because of the drought. From 2007 to 2009, California’s water problems were dire. Lacking irrigation water, growers let fields go fallow. Unemployment rates in some Central Valley farm towns edged above 40 percent. The drought also was blamed for ecological collapse in the Sacramento-San Joaquin River Delta, where the Sacramento River’s storied salmon run was on the brink of extinction.

In that crisis atmosphere, Schwarzenegger, Steinberg and other lawmakers crafted their emergency plan, which they said would solve California’s water problems for a generation.

But a wet winter followed, and California’s immediate water problems receded. Meanwhile, environmental groups, taxpayer advocates and some labor unions lined up against the water bond, calling it too expensive, laden with pork and environmentally destructive.

Fearing that the measure would fail, Schwarzenegger induced the Legislature to postpone the vote to 2012.

But since then, the political climate for the water bond may have deteriorated further.

Voters are well aware of the state’s precarious finances; they might be skeptical of the water bond’s price tag.

“All everybody’s been talking about is an $11 billion bond when we’re broke,” said John McManus of the Earthjustice environmental group.

The back-to-back wet winters also may change the dynamic.

“If you are in the middle of a drought, voters are much more sensitive to the issue, even though if you pass the bond. it’s going to be two or three years before you build anything,” said Joseph Caves of the Conservation Strategy Group, political consultants on the bond campaign in 2010.

Wet winters or no, California needs to solve the problem of how to guarantee a water supply to its growing population, advocates say.

“If I had my way, we wouldn’t talk about drought anymore,” said Mark Cowin, director of the state Department of Water Resources. “We live in a state that has variability in water supply. Climate change is only going to accentuate it.”

California needs to continue to “invest in conservation, recycling and water storage projects,” he said – all measures that the water bond sought to fund. Scaling it back isn’t simple.

“It’s very difficult to get an analytic approach of how big (the bond) should be,” he said. “Clearly, the governor is concerned about levels of debt – that’s the real driver for considering reducing the size of the bond.”

Whether to scrap the proposed big dam on the San Joaquin will be “part of the conversation,” he said.

Today, Cowin said the state’s water supply is in good shape. But it’s a year-to-year thing.

In the coming winter, “it appears as if we’ll experience moderate La Niña conditions,” he said. “Typically, what that means is the Northwest is wetter than usual and the Southwest is drier than usual. And here in Northern California, it can swing either way.”

This story was published originally on California Watch, a project founded by the Center for Investigative Reporting, and a content partner of KQED and Climate Watch. You can contact the writer at lwilliams@californiawatch.org.

Patrick McCully/Flickr

Demonstrators rally in 2006 for the removal of dams on the Klamath RIver.

Today at the Commonwealth Club in San Francisco, Secretary of the Interior Ken Salazar weighed in on three major water projects in the state and called on Californians to “stand firm” and defend the “hard-gained agreements and settlements” built in past decades.

“Never before have water agreements that provide safety and certainty for Westerners been so at risk,” said Salazar, referring to debates over the future of the San Joaquin River, the California Bay Delta, and the Klamath River.

Salazar argued that the state, and the country, should not back away from the 2006 San Joaquin River Restoration Program settlement, which, he said enabled the river to run from its headwaters to the ocean this year for the first time in half a century. He lobbied for the Bay Delta Conservation Plan, calling it a “comprehensive approach that includes new habitat for endangered fish species, coordinated measures to attack toxics that are fouling delta waters, and improvements to the state’s water infrastructure.”

Salazar said he will be ruling on the proposal to remove four dams along the Klamath River in March of next year.  In recent years both fish populations and agricultural interests have suffered from drought along the oversubscribed river.  In 2009, negotiators representing a wide array of interests agreed on a settlement that would remove four hydroelectric dams by 2020 as part of an agreement to restore historic salmon runs while keeping irrigation for the region’s farmers.

Salazar said Monday that the cost of removing the dams would be $290 million, far less than the $450 million originally estimated. He offered a preview of the impacts of the dam removals and river restoration, according to the DOI’s Draft Environmental Impact Statement, which is due to be released Thursday. The report includes the following findings, he said:

• Loss of hydroelectric power
• Loss of 50 power generation management jobs
• Loss of some recreational opportunities
• Decrease in some nearby property values
• Addition of 4,600 jobs to the regional economy over 15 years, including 1,500 during dam removal
• Increased water reliability to boost farm income and add between 70 and 695 agriculture jobs annually
• Improved conditions for salmon fishermen, creating 400 jobs

Salazar said that California and the West are facing a critical time for decisions about the region’s water supply.  Both population growth and climate change will add stress to an already stressed system, he said.

“Climate change is happening,” he said. “We can’t ignore this reality. It does no good to blame the scientists or to bury our heads in the sand.”

Craig Miller

Scientists and planners expect the Bay Area to face a host of water-related threats in the coming decades due to climate change, including flooding due to rising seas and summer water shortages due to warmer temperatures and a shrinking Sierra snowpack.

A new analysis released Tuesday from the non-profit Natural Resources Defense Council catalogs these threats, for San Francisco, and for 11 other American cities, including Los Angeles. The study also looks at how prepared the cities are to adapt to these climate challenges. It finds, in general, that San Francisco is leading the way when it comes to being prepared.

“San Francisco is doing a good job laying the groundwork,” said Michelle Mehta, the lead author of the study. “The first step is coming up with really robust science-based plans, and so far San Francisco looks like they are doing a good job of that.”

She said San Francisco is particularly vulnerable to flooding due to rising seas, which, according to current projections, could rise 55 inches by the end of the century.

According to the report:

“High-sea-level events will cause flooding, erosion, damage to coastal structures and real estate, and salinity intrusion, particularly of low-lying land bordering San Francisco Bay and the Sacramento-San Joaquin River Delta. Increased salinity in the Delta would degrade the quality and reliability of the fresh water supply used for drinking water and agricultural purposes. Shoreline development located in the area’s 100-year floodplain could be subject to a 100 percent chance of flooding by mid-century. Sea level rise also threatens critical infrastructure.  Approximately 235 hazardous material facilities would be at risk of a 100-year flood with a 55-inch rise in sea level.  Wastewater treatment facilities, 12 power plants, 1,900 miles of roads and highways, and two major airports also would be vulnerable with a 55-inch rise.

The report also finds San Francisco vulnerable to summer water shortages due to warmer temperatures that will cause more of the state’s precipitation to fall as rain rather than snow and will force the Sierra snowpack to melt earlier in the year, “altering traditional runoff patterns and complicating water supply management.”

The good news, said Mehta, in that San Francisco is paying attention.

“San Francisco is, I think, ahead of the curve compared to other cities in terms of their greenhouse gas mitigations and in terms of looking how to become more resilient to these impacts,” she said.

The report lists some of San Francisco’s climate change strategies and cites them as, “examples of the steps that communities across the country should consider.”  According to the report:

• In 2008, the San Francisco Board of Supervisors set new goals to reduce emissions by 25 percent below 1990 levels by 2017, 40 percent by 2025, and 80 percent by 2050.
• In November 2010, the city formed an interagency task force to develop policies to address potential future flood associated with sea level rise.
• The San Francisco Public Utilities Commission (SFPUC) is working with the National Oceanic and Atmospheric Administration (NOAA) to conduct an assessment of how climate change will impact the SFPUC system.
• The San Francisco Bay Conservation and Development Commission (BCDC), which is the state agency responsible for regulating development in the Bay Area, has proposed incorporating sea level rise scenarios in the permitting process, to develop a longterm strategy that considers local impacts of climate change, and to include policies that promote wetland protection, creation, enhancement and migration.

The report singles out Los Angeles as being particularly vulnerable to water-related climate change impacts, citing rising seas and increasing temperatures that will both likely affect water supply, and recommends that the city continue to work to reduce water consumption and supplement supply with reclaimed wastewater and stormwater.

A new study finds large losses of springtime snow cover in the West in recent years, raising concerns about water supplies.

Spring snowpack in the West is an essential water resource, particularly in Southwestern states that are prone to summer drought, like California, Nevada, Arizona and New Mexico. (Credit: Wolfgang Staudt on Flickr)

Head south across the 40^th parallel, however, and things are dramatically different. While there is still above average snow throughout the Sierra, a relatively snow-less winter and spring has left much of the Southwest in a drought that has fostered record wildfires. Already local officials are worried there won’t be enough water to get through the summer months ahead.

This kind of contrast for the western spring snowpack is not unusual, though. It’s completely normal, and it’s exactly what climate scientists and meteorologists expect during years when the average weather pattern is influenced by La Niña, a climate cycle associated with cooler than average water temperatures in the tropical Pacific Ocean.

But while this north-south dichotomy turns out to be a regular feature of western climate, new research published today in the journal Science shows that, when compared to typical snowfall during the past 1,000 years, snowpack patterns appear to be changing as average temperatures climb. Scientists say that as temperatures continue to rise, this reduced snowpack will lead to more frequent water shortages in increasingly thirsty western states.

“We’re talking about simultaneous snowpack decline in the western watershed that supports 70 million people,” says U.S. Geological Survey (USGS) climatologist Julio Betancourt, who co-authored the new study. “We have to be concerned.”

For several years, scientists have observed that spring snowpack all across the West — in both northern and southern areas — has been decreasing. But now, Betancourt and a group of other climate scientists have found that the recent decline is a departure from patterns of the past 1,000 years. As part of the study published in Science, USGS ecologist Greg Pederson investigated tree ring data to learn how snowpack in the West, on either side of 40^th parallel, changed from year-to-year and from decade-to-decade. Looking back over nearly a millennium, he found that when the north had high snowpack, the south typically experienced low snowpack, and vice versa.

But Pederson and Betancourt noticed a change starting in the mid-1980’s. On average, the amount of snow on the ground at the beginning of April each year was decreasing everywhere across the West. It’s a trend that other scientists studying snowpack have pointed out. This has important consequences for water supplies for drinking water and agriculture, since many areas, including much of interior California, are dependent upon spring runoff for much of their water supplies.

Betancourt says that as average spring temperatures have risen, the snowpack has begun to melt earlier in the year (not the case this year, with record cold weather locking in substantial amounts of snow in many western ranges). Moreover, he says that in many places, the warmer temperatures mean that precipitation falls more as rain than as snow. So while the actual amount of precipitation hasn’t changed dramatically, the amount of rain has.

Snowpack in much of the West remains well above average, thanks to a cold and snowy winter and spring. In the Southwest, however, snowpack was well below average. (Image: NRCS)

“Snowpack is the water resources of the West,” says Greg McCabe, a USGS hydrology expert who was not directly involved in the new study, “and temperature has a dominant impact on the snowpack.” If warming temperatures in the West cause the snowpack to decrease even more, McCabe says, or if the timing of the melt each spring changes, then summer water shortages could happen a lot more often.

McCabe says the research provides valuable evidence about how snowpack has changed historically, and also how unusual the recent patterns appear to be.

According to Pederson and Betancourt’s findings, the way snowpack has changed in the past 30 years isn’t entirely unprecedented. There were two brief periods in the mid-1300’s and early 1400’s where there was less snow built up throughout the West.

“At both those other times in the past, we know it was warm then too,” explains Betancourt.

Now, however, climate scientists are predicting that average temperatures in the West are going to keep rising this century, due in large part to the buildup of greenhouse gases in the atmosphere. Compared to the past, when snowfall returned to normal as temperatures dropped, researchers now expect that warmer spring weather could keep spring snowpack on the decline for years to come.

“What’s happening in the spring for snow is critically important [for water availability] compared to what is happening in the dead of winter,” says Betancourt.

So what do the authors make of a year like this, which has brought frequent snowfall to the Sierra, even into June?

“There isn’t anything that has happened this year that isn’t consistent with what our new findings are,” says Pederson. Even as average temperatures increase in the coming years, there will still be cool years where above average snowpack builds up in parts of the West, particularly during La Niña years. “But these years will tend to be weather noise over top of the larger climate changes we will see over many years,” he says.

NPR’s Richard Harris interviews Pederson in this story for Morning Edition.

A version of this post also appears at Climate Central, a content partner of KQED Climate Watch.

Lake Mead, the Colorado River's largest reservoir in May, 2010 (Photo: Gretchen Weber)

The Colorado River is a critical source of water for more than 30 million people throughout the western United States. California alone gets more than a trillion gallons of water each year from the Colorado. But over the years, recurring droughts and the growing demands of urban populations have stressed the river system, which the Bureau of Reclamation now characterizes as “over-allocated.”  In efforts to plan for the region’s future water needs, the agency, in collaboration with Western states, has undertaken a two-year study to look at what lies ahead for the river and the cities, farms, and families that rely on it.

On Monday, the agency released the first interim report of the “Colorado River Basin Water Supply & Demand Study,” which projects changes in the river’s flow under four different scenarios. A model that incorporates predicted impacts of climate change shows a nine percent reduction in the Colorado’s flow within 50 years.  The study also projects more frequent and more severe droughts throughout the system.

According to the report:

“Under the Downscaled GCM Projected scenario, the mean natural flow as measured at Lees Ferry over the next 50 years is projected to decrease by approximately 9 percent, along with a projected increase in both drought frequency and duration as compared to the observed historical streamflow record. Droughts lasting 5 or more years are projected to occur 40 percent of the time over the next 50 years.”

That likely means harder times for those who rely on a river that already has little water to spare.

In a statement Monday, the Environmental Defense Fund (EDF) applauded the study’s focus on potential climate change impacts, but urged the agency to find ways to address the supply/demand imbalance while still maintaining “healthy” river flows.

“The economic well-being of rural communities and major cities in the basin are inextricably linked to the environmental health of the Colorado River itself,” said EDF’s Rocky Mountain regional director, Dan Grossman. “And just as human health depends on healthy blood flow, the Colorado River’s health depends upon healthy water flows that are being compromised by current management practices and policies, as well as a warming climate.”

The next interim report is expected in the Fall of 2011, and a final report is due in July of 2012.  According to the Bureau of Reclamation’s website, the study will, “define current and future imbalances in water supply and demand in the Colorado River Basin and the adjacent areas of the Basin States that receive Colorado River water for approximately the next 50 years, and will develop and analyze adaptation and mitigation strategies to resolve those imbalances.”

Snowy trees in Truckee, in February. (Photo: Lauren Sommer)

Surveyors from the Department of Water Resources strapped on their skis today and headed out to measure the status of the Sierra snowpack for the fifth and final time this season.  As expected, they reported good news for the state’s water supply.

It’s been a big year for the snowpack – the biggest since 1995 – and the snow’s water content is about 180% of what’s “normal” for early May. The spring melt has already begun, so there’s less snow than there was month ago.  Historically, early April is when the snowpack is at its peak, as it was this year.  And yet, the current water content of the snowpack is still 50% higher than the historic average for April first.

All this water has prompted officials to project water deliveries of 80% of requests from farms and towns served by the State Water Project this year.  That’s the highest percentage since 2006. Last year just 50% was delivered.

And yet when I asked DWR snow survey master Frank Gehrke if this year’s snowpack was record breaking, he chuckled a little and said, “Not even close.”

He said that today, the snow at Philllips Station, where he conducted one survey, had 33.7 inches of water content. In 1995, the water content on May first in the same spot was 44.7 inches of water content.  The maximum on record for early May, he said, was 64.7 inches.

“We went almost 6 weeks with no storm activity, and you’re not going to break any records when you go six weeks without any storms,” said Gehrke.

Yet, there is a lot of snow up there, and Gehrke said it will take awhile before it disappears from higher elevations.  In the meantime, the melt rate will increase with warmer temperatures and clear sunny days.

That, he said, could pose a flood risk in certain parts of the state, although he deemed it unlikely. What could toss a “monkey wrench” into that, he said, would be late-season storms bringing more precipitation that could tax the state’s storage systems.

“You’re coming in with reservoirs that have a lot of water in them already and with this large of a snowpack, there are some management issues,”  he said.

Most of the state’s reservoirs are above normal for this date, and the state’s two largest, Oroville and Shasta, are both more than 90% full.

Current conditions in key California reservoirs as of May 1. Click the map for a larger version. (Source: DWR)