New pests, a shrinking water supply and rising temperatures will alter agriculture in California.

Craig Miller

Tightening water supplies, encroaching pests and dwindling winter "chill hours," vital to many crops, are just some of the climate challenges facing California farmers.

Heat and Harvest, a new series from KQED Science and the Center for Investigative Reporting looks at the multiple climate challenges confronting California farmers. It’s no trivial matter. California’s Central Valley is widely known as “the nation’s salad bowl,” and there’s more than bragging rights at stake. Ag contributes more than $30 billion a year to the state’s economy.

Previously, Climate Watch has focused on efforts in the ag sector to conserve water or lower the carbon footprint. Some farmers are trying new technologies, others are experimenting with renewable energy. But meeting climate challenges on multiple fronts will, for some farmers and ranchers, be a matter of survival.

Here are links to some previous reporting from Climate Watch, from ag’s potential role in California’s emerging cap-and-trade program for carbon emissions, to innovation on the renewable energy front and new conflicts over land use.

Planting the Seeds for Greener Farms
Supporters of sustainable agriculture are looking forward to some “sustenance” of their own, after an eleventh-hour win in Sacramento. The new bills lays out an approach for ensuring that all proceeds from the sale of cap-and-trade permits be used to further reduce greenhouse gas emissions. Among the eligible activities listed in the bill are farming and ranching practices that reduce greenhouse gas emissions and sequester carbon.

Satellites Help Save Water on California Farms
Engineers at NASA and CSU Monterey Bay are developing an online tool that can estimate how much water a farm’s field might need. Satellites orbiting the earth take high-resolution pictures which are combined with on-the-ground data from farms.

Making Hay While the Sun Shines: A Flap over Solar Panels in Farm Country
Sun and open land make the San Joaquin Valley ideal for growing crops. But they’re also attracting an increasing number of large-scale solar power developers to the region. And that’s generating debate over whether farming the sun is really farming.

Making Renewable Energy from Farm Waste
California is just a few votes away from changing the rules to allow farmers to connect machines that create bioenergy to the electrical grid, a privilege that has thus far been reserved for farm-generated wind and solar energy.

New Map for Gardeners Won’t Help California’s Green Thumbs
It’s been more than two decades since the U.S. Department of Agriculture updated its Plant Hardiness Zones Map, used by gardeners across the country to determine what will grow in their yards. The new GIS-enabled map unveiled this week is a boost to people who live in places that get a lot of cold weather and may be seeing slightly warmer average winters now. Despite the new level of detail in the map, gardeners in California and the Bay Area in particular, won’t learn much from it.

Craig Miller

Californians may want to rethink the long-established tradition of watering the sidewalk.

You installed a low-flow toilet. You take fast showers. Your yard is water-wise and drought-tolerant. And even if everyone in California were just like you, which they’re not — yet — the state would still see a significant bump in urban water demand by the end of the century. The culprit: warmer temperatures caused by climate change.

An innovative new model developed by researchers at Oakland’s Pacific Institute shows that even if California meets its current goal of reducing per-capita water usage 20 percent by 2020 — and continues to improve water efficiency at a similar rate through the end of the century — still, by 2100 the state’s urban water demand will increase by eight percent, or roughly one million acre-feet (with all other factors held constant). That’s a lot of water: enough to satisfy the current household needs of 6.7 million Californians.

The result came as a surprise even to model co-creator Juliet Christian-Smith. “Warming overwhelms the efficiency improvements,” she said. Here’s why, in a nutshell: warmer temperatures lead to higher evaporation and respiration from plants. It may sound trivial, but it’s serious stuff. Up to half of California’s urban water use takes place outdoors, including at golf courses, parks, and other large landscaped areas. As temperatures increase, it takes more water to hydrate the same plants. (The one million acre-feet figure is based on temperatures associated with a medium-high greenhouse gas emissions scenario.)

It’s also worth noting that at a certain point — around 2080, Christian-Smith projects — the residential efficiency measures that Californians have been slowly adopting since the 1980s will cease being quite as effective. By the end of this century, if we stay on track, enough homes will have low-flow toilets, shower heads, faucets, washing machines, and dishwashers that their benefit will become less pronounced. At that point (what you might call the “saturation point”), we’ll really need to focus on reducing outdoor water use through low-water landscapes and widespread use of reclaimed water.

The Pacific Institute’s new model isn’t just designed to offer another spin on global-warming doom and gloom — or to pooh-pooh your new toilet. Rather, it’s designed to offer a useful tool to water agencies hoping to plan for the future. It’s particularly targeted toward cities and local agencies that lack the ability to develop their own models, Christian-Smith said.

“This tool will allow smaller agencies that don’t have any modeling staff to run some scenarios and potentially include those in their water management plan,” she noted. It’s even available for free to armchair hydrologists. You can download it and an accompanying report, which explains how the model was created and examines a series of six state-level scenarios, at the Pacific Institute’s website.

Craig Miller

The new normal? A temperature display in the Kern County town of Taft shows 105 degrees on a late afternoon in July.

Granted, it’s been a relatively cool summer in many parts of California. But state officials are saying, “Don’t get used to it.” How would you like to see the number of “extremely hot” days (105 or hotter) in Sacramento increase fivefold in the next few decades? That’s just one of many new projections from the state’s latest official climate assessment.

One hundred-twenty scientists worked on the report, entitled California’s Changing Climate (PDF). Funded by the California Energy Commission, it’s actually a portfolio of studies and contains some of the most specific warnings we’ve seen. For instance, it projects that going forward, average temperatures in the state will warm at three times last century’s pace. It’ll mean heat waves happening more often and lasting longer.

And there’s new evidence from a refined set of models that the state will be drying out. “By mid-century, already we’re seeing a drying trend which could be up to ten percent drier by the end of the century, says Susanne Moser, identified as the principal researcher for the report, “and that is significant for a lot of people.” Especially if you live in say, the San Joaquin Valley, where the report projects that the frequency of “dry years” could increase by about a third in the “latter half of this century,” compared to the late 20th century.

And authors expect the weird weather to get worse, projecting that as soon as 2050, what’s now considered a 100-year storm could become ‘an annual event.”

State officials nearly fell over each other to say that it’s not too late to blunt some of the worst effects, however, with astute planning and aggressive action to reduce global warming emissions. Ken Alex, who heads Governor Jerry Brown’s Office of Planning & Research, characterized the mounting climate threats as, “a series of plagues,” but added that, “we’re not helpless. We need to adapt and we need to understand what that adaptation requires.”

Some interesting numbers from the study:

• 1.7: increase in statewide average temp from 1895 to 2011, in degrees Fahrenheit
• 2.7: likely increase by 2050, compared to 2000
• 20: Number of days per year that the temp could reach 105 in Sacramento by 2050 (versus four, historically)
• 10-18: Likely range of additional sea rise along California by 2050 (v. 2000)
• 23: Number of San Francisco fire stations that would likely be inaccessible with 16 inches of additional sea rise (considered likely by 2050)

CA Climate Change Center

Scientists say how much temperatures eventually rise will depend on the pace of continued global warming emissions.

The study suggests that temperatures will rise more in the summer and inland, with springtime warming “particularly pronounced” and fewer cold nights. Farmers depend on chilly nights to produce some high-value crops, such as stone fruits. Officials at the Energy Commission expressed concern about potential impacts that rising temperatures will have on the state’s power grid, some of which we addressed in a previous post.

As for reducing emissions enough to make a tangible difference, Moser concedes that’s not a job that California can do alone. But she said this report is the first to target findings to the kinds of questions that officials and planners have been asking (like the aforementioned matter of how many triple-digit days they can expect–and how soon).

Craig Miller

Rare summer rain clouds approach a farming valley near the Coast Range, west of Bakersfield.

A new report suggests that global warming is playing out quite differently in California, depending on whether it’s north or south of San Francisco Bay.

The project, by the Environment California Research & Policy Center, studied precipitation trends between 1948 and 2011, with an eye on “extreme” events — storms that dumped unusual amounts of rain or snow on the state.

They found a dichotomy in California — but not the usual “north has all the water” split. It turns out that north of San Francisco Bay, the extreme precipitation events were happening 26% less often, but south of the Bay, they were happening 35% more often. The authors calculate that a storm that used to come along once a year on average, is happening more like once every nine months to the south, which includes the Central Coast. In fact, Santa Barbara showed the biggest increase in frequency, 72% since 1948.

The report was part of a larger look at precipitation trends across the U.S., entitled “When it Rains, It Pours: Global Warming and the Increase in Extreme Precipitation from 1948 to 2011.” It concludes that nationwide, total annual precipitation is up nine percent over the period, and that on average, extreme rain and snow events are happening 30% more often. The authors define “extreme events” as those which have occurred no more than once a year, according to the historical record. Some might argue that once-a-year is a pretty low threshold for “extreme” but the trend is worth noting. Other scientific studies have taken a different approach, defining “extreme” as events that reside in the upper five percent of rainfall, temperature, or whatever is being studied.

Another finding was that big storms are getting bigger. This showed up most starkly in New England and the Mid-Atlantic states which, “saw the intensity of the largest storm each year increase by 20 percent or more,” according to the report.

The authors aren’t bashful about making the link between these trends and a warming planet, noting that warmer temperatures increase evaporation and the amount of moisture in the air:

“Scientists have found the water content of the atmosphere is now increasing at a rate of about 1.3 percent per decade. The additional moisture loaded into the atmosphere by global warming provides more fuel for intense rainstorms and snowstorms.”

“Heavy rainfall, heavy downpour events have been increasing and that is consistent with the fact that a warming atmosphere holds more moisture,” says David Easterling, who heads the Global Climate Applications Division for NOAA. He helped review the study but he’s at a loss to explain the north-south divergence in California.

The study shows that on average, in southern California, the big storms are getting not only more frequent, but bigger, whereas — again — the reverse seems to be true for most of the state north of San Francisco. Easterling says it appears that something is diverting the wettest winter storms, known as “atmospheric rivers,” to the south. He says the closely studied El Nino Southern Oscillation (ENSO) undoubtedly plays a role but then, he says, you have to ask how climate change is affecting the ENSO.

The study has not gone through a formal scientific peer-review process but Easterling told me that he’s impressed enough with the methodology and results that it should.

The report’s release comes just as state and local officials are gathered in San Diego for a workshop on planning for extreme weather events, and as California’s Natural Resources Agency prepares to release a major update in its series of periodic climate assessments.

Scott Olson/Getty Images

1. “Drought’s Footprint” — The New York Times

In June, more than half of the U.S. was experiencing moderate to extreme drought. How does that compare to other years? The Times’ graphic lays it out.

2. “Dried Out: Confronting the Texas Drought” — NPR, KUT and KUHF

The drought began in Texas in October of last year. Watch it grow over time, and explore a timeline that explains the root causes of the drought and how communities are responding.

3. “Flash Drought in U.S. Explained in 14 Seconds” — Climate Central

Watch an animation showing the spread of the drought, from Texas and Georgia in March, to most of the Midwest and West by June.

4. Drought Impact Reporter — The National Drought Mitigation Center

This is “the nation’s first comprehensive database of drought impacts.” Submit reports of how the drought affects you, and search for drought impacts by state, whether they’re to agriculture, industry, public health or wildlife.

5. “Historic heat wave in hindsight: Hottest on record in Washington D.C., hotter than 1930″ — Washington Post

From the Post’s weather blog, a local, numbers-heavy analysis of the heatwave that hit Washington. With stats like “Longest period at or above 100: 7 hours on July 7 (tie with July 6, 2010 and July 21, 1930),” it’s like a Guinness Book of World Records for D.C.’s summer, and holds my usually California-focused attention.

Craig Miller

Opponents to Governor Brown's Delta plan were gathered on the Capitol steps within an hour of the announcement.

You can hear a one-hour discussion of the proposed Delta plan on KQED’s Forum.

“You’ve launched a war. We’ll fight the battle,” was the rallying cry from congressman John Garamendi, within hours of the announcement of Governor Jerry Brown’s revised plan for California’s already embattled Sacramento-San Joaquin Delta.

Brown was flanked by U.S. Secretary of the Interior Ken Salazar and officials of the National Oceanic & Atmospheric Administration in rolling out a plan which Brown’s Natural Resources Agency says, “will undergo a rigorous public environmental review.” The plan’s centerpiece is a long-debated tunnel to shuttle water from the Sacramento River, north of the Delta, to the vast plumbing system that carries water to farms in the San Joaquin Valley and cities in Southern California. The conveyance is touted as a way to protect fish from the voracious pumps that fill the canals heading south.

Opponents were quick to muster their troops in Sacramento and Washington. On the steps of the state Capitol, Delta congressman John Garamendi fired a classic shot in California water wars, telling a crowd of tunnel opponents and onlookers that Brown’s plan is, “the junior water rights-holders once again making a grab for northern California water — that’s what it’s all about.” The “junior rights-holders” he referred to are the agencies and contractors who supply Delta water to the San Joaquin Valley and Southern California.

“They have put plumbing before policy,” said Garamendi. Invoking the film, “Field of Dreams,” he said, “They intend to build it and then figure out how it can be used.”

How it might be used troubles the Delta Democrat, who calculates that the combined throughput of the twin tunnels could easily divert half the volume of water that typically flows past Sacramento toward the Bay.

“We can’t let it happen,” said Garmendi. It’s the Delta. It’s the lifeblood of the SSJD and SFB. There’s a better way of doing it. Let the science dictate what should happen.”

Brown and his federal flankers insist that the plan is “grounded in science,” and an improvement over previous proposals. Planners are, “closer then ever to forging a lasting and sustainable solution,” said Salazar in a news release.

Lois Wolk wasn’t buying it. The Democratic state senator from the Delta region said the plan, “stakes the future of the Delta on a wink and a promise. ‘Trust us,’ they say,’ to build two gigantic tunnels now, take the water, and protect the Delta later.”

Wolk said in the balance are billions of dollars in “higher water rates” and borrowing. She said more of California’s long-term water solution should lie in the “vast potential” of water conservation, recycling, and other technologies such as desalination.

Republican assemblyman Bill Berryhill, who farms his own patch of the Delta, voiced concern that the project, estimated at $14 billion, would become “another Bay Bridge,” a reference to the new San Francisco Bay Bridge currently under construction at a cost that has increased six-fold since it was first approved.

But the Governor waved off the naysayers with impatience and an unusually public expletive. “I want to get s**t done,” he told reporters at the announcement, “and I want to get this thing done the best I can, all right?”

And just in case you’re among the eight-in-ten Californians that can’t quite conjure up a mental image of the Delta or why it’s important, KQED’s Matthew Green has an expansive backgrounder  posted at The Lowdown.

Josh Cassidy/KQED

The Sacramento-San Joaquin Delta plays a crucial role in the state’s water supply.

On Wednesday, Governor Jerry Brown and Interior Secretary Ken Salazar are expected to announce a multi-billion dollar plan designed to fix California’s longstanding water war in the Sacramento-San Joaquin Delta.

Their proposal for a 35-mile water tunnel is set to reignite the fight over how water is exported from the Delta. The announcement comes just months after federal and state wildlife agencies warned that the proposed version of the project could have dramatic impacts on Delta fish.

Political wrangling over the governor’s announcement has already begun. Two weeks ago, 11 members of Congress [PDF] urged officials to release more details about the costs and benefits of the plan before moving ahead. Senators Feinstein and Boxer sent a letter in support of the plan and urged them to meet the February, 2013 deadline to complete it.

History of Controversy

The Delta isn’t a place that most Californians know much about, as recent polls have shown, but the inland estuary just east of San Francisco Bay plays a crucial role in the state’s water supply. Delta water is pumped hundreds of miles across the state, reaching Silicon Valley, Southern California cities and millions of acres of farmland in the Central Valley.

California’s dependence on this supply has come with an ecological cost. Ten years ago, fish populations in the Delta crashed, including Delta smelt and longfin smelt. Numbers of endangered Chinook salmon were so low in 2008 that the commercial salmon fishery closed for two years.

Scientists point to a number of causes for this: loss of habitat, pollution, poor ocean conditions for salmon. But studies have shown significant fish losses at the massive pumping facilities in the south Delta, where water that would normally flow out to San Francisco Bay is diverted south. Others say that in some years, too much water was exported, not leaving enough in the ecosystem.

KQED / Bill Lane Center

California's Deadlocked Delta: Explore our series on the Delta.

After a decade of litigation over water exports, the state began developing the Bay Delta Conservation Plan, largely financed by the water contractors that use Delta exports. The plan revives the idea of the “peripheral canal” – a massive water infrastructure project that would take water farther upstream of the Delta and divert it south. The plan also calls for 65,000 acres of tidal habitat restoration.

“The potential of the Bay Delta Conservation Plan is enormous for the state of California,” says Karla Nemeth of California’s Natural Resources Agency. “It would be the most significant upgrade and modernization of the water projects in decades.”

Raising a Red Flag

The plan contains several alternatives for the “peripheral tunnel,” both in size and location. Earlier this year, the leading proposal was to build the largest tunnel facility with a capacity to move 15,000 cubic feet per second of water. A state analysis showed that it would export near-record volumes of water from the ecosystem (see page 34 [PDF]).

That raised concerns with wildlife agencies, including the U.S. Fish and Wildlife Service and the California Department of Fish and Game. The agencies have the power to approve or deny a permit for the project based on its impact to endangered Chinook salmon and Delta smelt.

In April, the two agencies released a document [PDF] listing their concerns. “We need to be able to make a finding that the project as a whole is going to contribute to the recovery of the species,” says Carl Wilcox of the Department of Fish and Game. “If the analysis says, well, they’re going to do worse under the plan, we’re not going to be able to permit it.”

The plan showed an impact on endangered winter-run Chinook salmon, which depend on spawning ground below Shasta Dam. “The water quality conditions were going to be degraded to the point where they were going to be further jeopardized,” says Wilcox. “Longfin smelt is dependent on a certain amount of outflow through the Delta in the spring to achieve positive population growth. And what we were finding was that wasn’t going to be achieved and the population was going to decline.”

Since then, Wilcox says talks with the Bay Delta Conservation Plan writers have been productive. “Consequently, we expect to be seeing a change in the proposed project to respond to those concerns.”

That appeared to be the case at the Bay Delta Conservation Plan meeting in June, where officials referenced a smaller tunnel project that would move 9,000 cubic feet per second.

“We’ve been taking a look at some of the footprint issues,” says Nemeth. “We are very concerned about impacts to local communities and looking at ways where we can size a facility that can deal with securing water supplies and that can advance the recovery of fish species. That’s been the primary driver for the sizing of facilities as smaller as what had been proposed in February.”

Opposition Heats Up

The most heated criticism of the plan has come from groups representing farmers and communities in the Delta, concerned about the construction footprint. “Governor Brown’s plan, an enormous mistake, would exterminate salmon runs, destroy sustainable Delta family farms and saddle taxpayers with tens of billions in debt, mainly to benefit a small number of growers on the west side of the Central Valley,” said Restore the Delta, in a recent statement.

Financing the plan may still be the largest hurdle for the state. Water users would pay for the construction of the $13 billion tunnel, while funding for habitat restoration would come from state and federal sources, including part of the $11 billion water bond, recently pushed back to the 2014 ballot.

Water users haven’t come out against the smaller tunnel, but say deliveries will still be their bottom line. “It depends on how the 9,000 CFS project is operated,” says Jason Peltier of Westlands Water District, an agricultural area that depends on Delta water.

“If we build a 9,000 cubic feet per second diversion but the fishery agencies say you can only operate it this minimalist amount of time, it’s not going to provide the water supply and reliability benefits that we’re looking for. And maybe we don’t have a project.”

Still, Peltier says they’re willing to work with the state over the next decade as more scientific study is done. “We’ve evolved our thinking in recognizing that we can’t today, with anything other than a guess, say how the project will be operated in 15 years.”

Despite the fact that previous planning efforts have failed, Peltier believes that this time there’s a consensus on all sides that a solution needs to be found. “To not decide is to decide, also, and inaction is unacceptable. I think that’s a pretty uniformly felt feeling.”

A version of this post originally appeared on KQED’s News Fix.

By Andrew Freedman

Scott Olson/Getty Images

A cow feeds in a drought-damaged pasture as temperatures climb near 100 degrees on July 17, 2012 near Princeton, Indiana.

Driven by a combination of natural climate variability, manmade global warming, and plain old bad luck, drought conditions are so widespread in the U.S. that it’s possible to take a cross-country flight from Washington, D.C. to San Francisco — a distance of approximately 2,400 miles — without once overflying an unaffected area. With about 81 percent of the lower 48 states experiencing at least abnormally dry conditions, and 63 percent mired in moderate-to-exceptional drought, it’s becoming harder and harder to find an oasis. And the dog days of August are yet to come.

The National Oceanic and Atmospheric Administration (NOAA) already ranks this drought as one of the worst on record, comparable to the drought events of the 1950s. The last time there were such widespread drought conditions in the corn-growing region of the country was in 1988, and that drought cost at least $40 billion.

Given this summer’s punishing 1-2 punch of dry weather and heat, this drought is also being compared to the Dust Bowl era of the 1930s.

According to Richard Seager, a professor at the Lamont-Doherty Earth Observatory at Columbia University and a prominent drought researcher, this drought has one key thing in common with the Dust Bowl and the 1988 drought events: its origins can be traced to the tropical Pacific Ocean, where a periodic cooling of sea surface temperatures — a phenomenon known as La Niña — helped reconfigure global weather patterns during the past two years.

Seager’s research has shown that La Niña is closely tied to many historical drought events in the U.S., since it shifts weather patterns in a way that favors a northern storm track, bypassing the southern tier of the country and depriving the already arid Southwest of much-needed moisture. Even though La Niña conditions are no longer present in the tropical Pacific — in fact, there is talk of a coming El Niño, with warmer sea surface temperatures — the weather pattern in the tropical Pacific is still behaving in a manner that is more consistent with La Niña. This may be giving the 2011-12 La Niña an extended lifespan in the U.S., Seager and other climate scientists said.

“La Niña conditions are perfect for getting drought in the southern parts of the U.S. There is absolutely no doubt that that has been a large part of what’s been going on here,” Seager said.

Seager and other experts noted that factors besides La Nina are also playing a part in this drought, however.

Unlike the droughts of the 1930s, this one is occurring in a much warmer climate, a byproduct of manmade global warming. Seager said that although it most likely didn’t trigger the drought, it’s possible that global warming is making this drought worse than it would otherwise be.

“I think what we’re seeing is largely a naturally occurring event, but it’s occurring against the background of a warming environment,” Seager said.

Global warming may be affecting the feedbacks that take place between dry soils and the atmosphere. When soils dry, very little evaporation occurs and very little moisture is released from vegetation to the air. This can accelerate warming, making droughts hotter, and therefore even drier. Mark Svoboda, a climatologist at the National Drought Mitigation Center in Lincoln, Neb., said this phenomenon is known as drought “feeding on itself.”

Such feedbacks have helped the current drought rapidly balloon in size, overtaking some regions so quickly that it’s referred to as a “flash drought.” At the start of the year, just 28 percent of the contiguous U.S. — mainly the southern tier — was in at least moderate drought. Between mid-April and mid-July, the moderate to exceptional drought area went from 37 percent to 63 percent, a clear indication of the toll that the hot, dry spring and summer have taken.

Kevin Trenberth, a senior scientist at the National Center for Atmospheric Research in Boulder, Colo., said global warming helps make droughts hotter, and therefore drier, than they would be without a human influence. Manmade global warming, he said via email, “. . . means more energy that has to go somewhere. In dry conditions it amplifies drying and goes into heating, creating heat waves. It is small on a day-to-day basis, but is always in one direction and it creates stronger, more intense, and longer-lasting drought. No doubt about it.”

Seager pointed to the lack of snow cover from the 2011-12 winter as another key factor in the drought’s expansion. In Colorado, for example, there was an unusually thin snowpack that melted earlier than average. This primed the state for destructive wildfires and record warm temperatures during June. The thin snow cover and early melt across the High Plains also may have helped dry soils in that region, and may have affected larger-scale weather patterns.

According to Svoboda, the below-average snowpack was one of the factors, along with a dry and warm spring, that made the U.S. more vulnerable to drought come early summer. “We had two strikes against us before even getting to the summer or the heat wave that would follow,” he said in an email conversation.

“I don’t attribute this drought to global warming, but we do see what increased temperatures can do to exacerbate droughts, and if higher temperatures become a more persistent feature in some regions not used to it, then this isn’t a good combination,” Svoboda said.

There is some evidence that this is already happening. A recent study found that global warming made the Texas drought and heatwave 20 times more likely to occur than under similar large-scale climate conditions 50 years ago. Other research shows that warming driven by human activities made the same heat wave and drought more severe than it otherwise would have been. As for whether global warming made the current drought more likely to occur, such “climate attribution” studies can take several months to complete, and the drought is still underway.

If indeed we’re already seeing more intense droughts as a result of global warming, it doesn’t bode well for the future, judging from what climate studies show. For example, climate research consistently shows the Southwest U.S. will become much drier as the climate continues to warm.

Seager’s own research has revealed a disturbing history of North American “megadroughts” that have lasted for decades, making the current event look quaint by comparison. And one study published in 2011 found evidence for a global warming-induced increase in aridity over global land areas since the 1970s, and noted that climate models project a huge expansion of drought areas in the coming decades, depending on whether and by how much greenhouse gas emissions are reined in.

In other words, if you think this drought is bad . . . just wait.

A version of this post also appears at Climate Central, Climate Watch’s content partner.

KQED QUEST

Scientists are looking at climatic water deficit, the water plants need but don't have.

We hear a lot about how climate change will affect rainfall in California, but climate scientists are increasingly looking at a new indicator: water deficit.

“Climatic water deficit” relates to how much water plants need to survive. “It’s the difference between what a plant would use if it had the water and what is actually available,” Alan Flint, research hydrologist with the US Geological Survey, explained on Wednesday at the North America Congress for Conservation Biology.

The value combines temperature, rainfall, the soil’s capacity to hold water and how plants use water. In agriculture, farmers irrigate their crops to make up the water deficit, but plants in the natural world aren’t so lucky.

Using modeling, Flint and his colleagues are finding that the Bay Area’s water deficit is likely to increase, even under a wetter climate future. “We see that excess water go to runoff in the wintertime. But if you’re a plant species trying to live in March and April and growing leaves, you only have the water that’s in the ground,” Flint said.

Warmer air temperature increases evapotranspiration – the water lost through evaporation from soil and from plants themselves. That increases a plant’s demand for water.

“Water deficit is going to be a big issue. It’s what will control the health of forests in the Sierra Nevada. It will control landscape changes in the Bay Area,” said Flint.

That could include oaks, which are often found on north-facing slopes in the Bay Area, “where the water deficit is low. On the south slopes, we don’t see them there,” said Flint. In a warmer future, “if those areas where oaks live have the same water deficits as the south facing slopes, the oaks may not be able to regenerate there. They may survive, but they may not be able to regenerate.”

Water deficits could also have a large impact in the Sierra Nevada, which Flint calls a potential “worst case.” Water deficits are associated with fires and with forest die-offs. “It will really stress the plants and allow bark beetles or other things to come in and kill them. And it doesn’t have to change by a lot,” said Flint.

By Andrew Freedman

Sasha Khokha/KQED

As soil dries, more of the sun’s energy goes into heating the air directly, rather than evaporating moisture from the ground.

Droughts such as the one currently gripping a majority of the U.S. may dramatically increase the odds of extremely hot days, a new study found. The study, published in Proceedings of the National Academy of Sciences, explores a dynamic that is playing out right now across the country, particularly in the Great Plains, where the severe drought is priming the atmosphere in favor of an above-average number of extremely hot days.

This occurs because of feedbacks between the ground and the air: as the soil and vegetation dry, more of the sun’s energy is able to go into heating the air directly, rather than going into evaporating moisture from plants and the soil.

With drought conditions intensifying during mid-summer, the study suggests that the U.S. may be in for particularly brutal Dog Days of August.

The study is the first to take a global look at the potential for weather forecasters to use precipitation data to help predict the likelihood for heat extremes. With heat killing more Americans per year than any other weather hazard, advance notice of heat hazards could help save lives.

The study looked at the relationship between dry periods and heat extremes that occur during the following month. They found that for much of the U.S., when precipitation falls below a certain threshold, there is a 70 percent likelihood of an above-average number of hot days during the following month.

The study indicates that drought not only increases the odds for the following month to have an above-average number of hot days, but it also makes extremely hot days more likely as well.

“. . . the occurrence probability of an above-average number of hot days is high after dry conditions and low after wet conditions” in certain areas, the study said. The study found that the drought and heat connection was clearly involved in intensifying the Texas drought of 2011, when the Lone Star State suffered through a brutal combination of heat, drought, and wildfires.

In an email conversation, lead author Brigitte Mueller of the Institute for Atmospheric and Climate Science at ETH in Zurich, said the current drought falls well below the study’s precipitation threshold, “which implies an even higher likelihood for an above-average [number of hot days] to occur.”

“Predicting the exact number of hot days would be difficult,” Mueller said, “because dry conditions can lead to both a high number of hot days or a low number of hot days . . . However, the prediction could include a probability for a high number of hot days.”

On the other hand, the study found that wet conditions help limit the occurrence of hot extremes in many parts of the world, and may even prohibit the occurrence of extremely hot days.

In addition to the U.S., the study found that precipitation may help forecasters anticipate heat extremes in Europe and a large portion of the Southern Hemisphere, too.

A version of this post also appears at Climate Central, Climate Watch’s content partner.