The extreme heat and dry conditions of the past few years pushed what was already an epic, decades-long drought in the American West into a historic disaster that bears the unmistakable fingerprints of climate change. The long-running drought, which has persisted since 2000, can now be considered the driest 22-year period of the past 1,200 years, according to a study published Monday in the journal Nature Climate Change.

Previous work by some of the same authors of the new study had identified the period of 2000 through 2018 as the second-worst megadrought since the year 800 — exceeded only by an especially severe and prolonged drought in the 1500s. But with the past three scorching years added to the picture, the Southwest’s megadrought stands out in the record as the “worst” or driest in more than a millennium.

“Without climate change, this would not be even close to as bad as one of those historical megadroughts,” said Park Williams, a climate scientist at the University of California at Los Angeles. “The thing that is really remarkable about this drought period is that temperatures have been warmer than average in all of the years but one.”

The double whammy of searing heat and persistent drought in recent years reflects the steady increase in global temperatures brought on by the burning of fossil fuels. The authors attribute 19 percent of the severe 2021 drought, and 42 percent of the extended drought since the 21st century began, to human-caused climate change.

This giant climate hot spot is robbing the West of its water

Scientists refer to this combined hot and dry effect as “aridity” — a warm and thirsty atmosphere that can pull moisture from soil and plants, melt snow, and intensify heat waves.

“All of the climate models agree that when greenhouse gases go into the atmosphere and temperatures rise, that’s going to enhance the ability of the atmosphere to pull water out of ecosystems,” Williams said.

This “background drying” brought on by a warmer atmosphere can dwarf occasional wet or cool periods. For example, the Southwest’s 2021 drought maintained its grip despite robust monsoon rains and record summer precipitation in some areas, in part because of extraordinary heat waves early last summer, and generally above-average temperatures.

The study’s tree-ring record also provides a sobering view of what is possible in the West. “The tree rings tell us that there can actually be very, very extreme dryness in the West without the help of climate change at all,” Williams said. “Even without climate change, we can have monumentally severe and long-lasting droughts.”

The study finds that the 21st century has been substantially drier than the previous five decades, with 8.3 percent less precipitation, and nearly 1 degree Celsius (1.8 Fahrenheit) warmer than the period from 1950 to 1999.

The American West’s drought isn’t a disaster. It’s our new, permanently arid normal.

And scientists have made clear that future warming could bring even more crippling and frequent droughts. Last summer, a report by the U.N. Intergovernmental Panel on Climate Change found that even as global warming can bring more extreme rainfall and flooding in some areas, it can also fuel more intense drought in many regions.

That analysis found that at the current warming trajectory, droughts in drying regions that previously occurred only once every 10 years are now happening about 1.7 times per decade, on average. If the Earth warms 2 degrees Celsius, scientists expect those once-rare events to take place roughly 2½ times per decade, on average.

But the West’s most recent megadrought isn’t just written in scientific data. It has manifested in the shrinking water levels of Lake Mead and Lake Powell, which last summer reached their lowest on record. These reservoirs have declined during the 21st century with rising temperatures, despite intermittent wet years.

The intensifying drought looks to continue in 2022 — unless a miraculous spring season brings a return of the storm track and moisture-rich atmospheric rivers.

Fueled by climate change, costly Southwest drought isn’t going away

While the study covers only the period through 2021, drought conditions have taken a turn for the worse in 2022. After a promising start to the wet season in December, unusually dry conditions have persisted over much of California since January.

California’s snowpack declined to just 73 percent of normal as of Monday, after being at 160 percent of normal in December.

The Central Sierra Snow Lab run by the University of California at Berkeley tweeted that its snowpack lost 5 percent of its water content amid unusually warm weather over the past week. At its monitoring site, the snowiest December on record has been followed by a record streak of 37 days without precipitation.

The parched conditions laid the groundwork for a recent record-setting winter heat wave in California.

From Wednesday through Sunday, the National Weather Service in Los Angeles issued the first heat advisory on record during the winter months in Southern California. Scores of record high temperatures were set, from San Diego to San Francisco.

Brush fires raged in Southern California amid record heat, worsening drought

Death Valley soared to 94 degrees on Feb. 11, its highest temperature recorded so early in the season.

The hot, dry weather, combined with gusty winds, fueled several brush fires in Southern California late last week. California has seen more than 12 million acres burn in the past decade, and 18 of the top 20 largest wildfires in state history have occurred in the past two decades.

Forecasters at the National Weather Service predict drought conditions to persist through the spring.

The authors of the paper also see no end in sight to the West’s arid reality.

“This drought will very likely persist through 2022,” they wrote, “matching the duration of the late-1500s megadrought.”

Williams said that tree-ring records do provide some reason for hope — megadroughts do eventually end when the rains return. Those rains are arriving in increasingly intense bursts as the atmosphere warms.

“The way you get out of droughts in the West is probably changing,” he said. Droughts may end abruptly during extremely wet years, like 2017, but then quickly reverse course again into another multiyear dry spell.

Brady Dennis and Jason Samenow contributed to this report.

Source: https://www.washingtonpost.com/weather/2022/02/14/southwest-megadrought-worst-1200-years/

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William Brangham:

The Colorado River is a critical source of water for the Western United States, but a mega-drought, one significantly exacerbated by climate change, is jeopardizing that river’s future, how that water gets used, and threatening longstanding agreements between states.

Miles O’Brien has our report.

It’s part of our coverage on how climate change is creating a tipping point for the U.S. and the world.

Miles O’Brien:

This is where the shortage meets the soil, Pinal County, Arizona, desert farmland between Phoenix and Tucson, lifelong home for farmer Nancy Caywood.

Nancy Caywood, Farmer:

My family has been farming in this area for 91 years. My grandfather bought this farm, 255 acres.

Miles O’Brien:

They grow alfalfa and cotton, both thirsty crops, which are not doing well right now.

Nancy Caywood:

This is the drought in action right here. I have never seen it this bad before.

Miles O’Brien:

Much of her water comes from canals that are filled by the Gila River, a tributary of the Colorado River. But in April of 2021, the water stopped flowing.

Nancy Caywood:

We don’t know when we will see water in here again.

Miles O’Brien:

Same goes for farmers in Pinal County who draw water directly from the Colorado River. When the U.S. government declared an official shortage for the river in August, farmers who depend on it were also drastically cut back.

Almost 1, 500 miles’ long, the Colorado winds its way through seven states and into Mexico. This river basin is filled with lush natural ecosystems. It transforms about 5.5 million acres of barren desert into fertile farmland; 40 million people are sustained by this water.

It’s one of the most heavily utilized rivers in the world, and it starts here, as a deep blanket of snow high in the Rocky Mountains of Wyoming, Utah, and Colorado.

Hydrologist Ben Livneh is an assistant professor at University of Colorado Boulder.

Ben Livneh, University of Colorado Boulder: Most of the of the water in the Colorado River starts as snowpack, and one of the reasons is that mountains act as these big catchments of precipitation.

Miles O’Brien:

But around the year 2000, a drought took hold and has not let go. This means less snow on those peaks in the Rockies year after year, and thus a steady reduction of water to feed the river.

The two largest reservoirs in the river basin, Lake Mead and Lake Powell, are now at all-time low levels. Climatologist Park Williams is an associate professor at UCLA. He uses tree rings to study the ancient climate.

Park Williams, UCLA:

The 2000s drought in the Colorado River Basin and across the Western United States has been as dry as any other 22-year period in the last millennium. The drought that we’re in today is not going to last forever, that it will break at some point when we have a string of really good luck years.

Miles O’Brien:

But the climate emergency has changed the odds. The global temperature is about two degrees Fahrenheit higher than it was before the Industrial Revolution.

Park Williams:

If climate change hadn’t happened, the West would still be in a drought, but the severity of the drought is undoubtedly worse because of climate change.

Miles O’Brien:

Here’s why. Warmer temperatures mean drier air. As the snowpack shrinks, it sheds water vapor into the atmosphere. A larger amount of snow melts into liquid water and rapidly evaporates in this warmer climate. Now the soil is dryer than usual.

Park Williams:

This causes the soils to act like a very dry sponge, and the next precipitation events that occurs on top of that dry sponge is going to work to refilling the soil sponge, as opposed to refilling our rivers and reservoirs.

Miles O’Brien:

This precious resource is allocated based on a 1922 agreement called the Colorado River Compact. Once the river basin states agreed on their fair shares, they each established a seniority system, first in time, first in right.

Ben Livneh:

There’s kind of a hierarchy of water rights. That means that people who gained access to the river first, they have what we would call a senior water right.

Miles O’Brien:

Colorado River water first came to Pinal County in the mid-1980s, upon completion of the Central Arizona Project, a network of canals that spans more than 300 miles across the desert.

It puts farmers here at the bottom of the seniority list, making them the first to go dry in the midst of this mega-drought.

Will Thelander, Farmer:

So, over the years, we have had to adapt to different whatever we can make money at, basically. So, on this farm, it’s really close to a bunch of dairies, and they need a bunch of feed.

Miles O’Brien:

Will Thelander is a third-generation farmer in Casa Grande. He and his family are part of an experiment in using their dwindling allocation of water on crops that demand less of it.

Will Thelander:

Here’s the guayule field. So you can see it’s in a nice bloom, and this crop hasn’t been watered for about two weeks.

Miles O’Brien:

They have planted a 40-acre tract of guayule, a plant that thrives in the desert and contains a milky latex that can be used to formulate rubber.

An acre can produce enough to make 50 tires. Bridgestone is working out the production kinks at this pilot plant, while Thelander does the same at this pilot plot.

Will Thelander:

With this crop, using half as much water as the corn, our water will last twice as long here. So that’s why the crop is so promising, and we really hope it takes off.

Miles O’Brien:

But for Nancy Caywood, the story is different. She can’t afford the cost of the new equipment required to harvest crops that need less water. She says she can hold onto the family farm for a year, but:

Nancy Caywood:

Eventually, the money runs out. You can’t pay the water and the taxes anymore. So it’s not your best interest to try to keep the land. Your best interest is to probably go ahead and sell. And it’s heart-wrenching to think that, but it’s true.

Miles O’Brien:

It would be the end of an era here, and maybe the beginning of a new one. Her neighbors recently sold their land, and it’s now a solar farm. Caywood has been approached by an energy company as well.

There is little to suggest this trend will reverse anytime soon. For years, humans overspent the Colorado River, and nature covered the overdrafts. But now the climate emergency has insured the bill has come due.

For the “PBS NewsHour,” I’m Miles O’Brien in Phoenix.

Source: https://www.pbs.org/newshour/show/unrelenting-drought-leaves-millions-who-rely-on-colorado-river-facing-an-uncertain-future

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Mexican and American officials have scheduled a signing ceremony on Sept. 26 in Ciudad Juárez, officials at California water districts said this week. They said that formal event will be followed by a ceremonial signing in Santa Fe, N.M., on Sept. 27 attended by representatives from the states involved.

“This is important to both countries, and will now allow the states and our federal partners to refocus back to drought contingency planning,” said Bart Fisher, chair of California’s Colorado River Board.

California water suppliers — including the Metropolitan Water District of Southern California, the Imperial Irrigation District and the Coachella Valley Water District — approved related agreements on Tuesday, taking some of the final steps necessary to complete the deal. California’s Colorado River Board also signed off at a meeting on Wednesday.

The new accord — titled Minute No. 323 to the 1944 Mexican Water Treaty — outlines a series of measures that build on the countries’ current five-year agreement, which expires at the end of this year.

The deal will extend provisions in the current agreement, known as Minute 319, that specify reductions in water deliveries during a shortage, as well as increases in water deliveries during wet periods. The agreement also provides for Mexico to continue storing water in Lake Mead, near Las Vegas, helping to boost the reservoir’s levels, which in the past few years have dropped to record lows.

A final version of the agreement has not yet been released. But according to a summary released by the U.S. Bureau of Reclamation, the agreement will establish a “binational water scarcity contingency plan,” in which Mexico will join U.S. states in temporarily taking less water out of Lake Mead to reduce the risks of the reservoir reaching critical levels.

Those commitments by Mexico would only take effect if California, Arizona and Nevada finish their own Drought Contingency Plan, under which the states would forgo larger amounts of water than they’ve previously agreed to as Lake Mead’s level declines.

The U.S. government has yet to announce details of the upcoming signing ceremony.

“We are very, very close,” said Lori Kuczmanski, a public affairs officer at the U.S. International Boundary and Water Commission in El Paso. “The signing date is not yet confirmed because we don’t have all the domestic approvals that we need. I expect that within the next week we will have that information and we can move forward.”

The agreement reflects the nations’ need to cooperate on water even as tensions remain over President Trump’s immigration policies and his plans for building a new wall along the border.

The Colorado River and its tributaries provide water for about 40 million people and more than 5 million acres of farmland.

The legal framework that divvies up the Colorado River was established during wetter times nearly a century ago, starting with the 1922 Colorado River Compact. That and subsequent agreements have handed out more water than what flows in the river in an average year, leading to chronic overuse.

On top of that mismatch between supply and demand, the river has dwindled during a 17-year drought. Climate change is adding to the strains on the river, and scientists have projected warming will likely cause the river’s flow to decrease by 35% or more this century.

Talks on the U.S.-Mexico agreement began during President Barack Obama’s administration and have continued with negotiating sessions convened on both sides of the border by the International Boundary and Water Commission, which includes representatives of both governments.

To complete the deal, U.S. water agencies and states needed to sign off on agreements including a U.S.-funded program to invest $31.5 million in water conservation projects in Mexico. Those projects will include infrastructure upgrades such as concrete lining for leaky canals and other improvements to reduce water losses from distribution systems.

The federal government will provide $16.5 million, while the remaining $15 million will come from four water agencies, including the Imperial Irrigation District, the Metropolitan Water District, the Southern Nevada Water Authority and the Central Arizona Water Conservation District.

Each of the water agencies will contribute part of the funding. In return, they will receive a portion of the water freed up through conservation in Mexico.

The conservation projects are intended to generate a total of 229,000 acre-feet of water — enough to cover an area two-thirds the size of Los Angeles with a foot of water. Of that, 50,000 acre-feet will be used to give a boost to the Colorado River system and 70,000 acre-feet will be used to “satisfy the U.S. commitment to provide water for the environment.”

After the U.S. water districts receive the remainder of that water, Mexico will be able to use the additional water supplies made available through the conservation projects.

The Imperial Irrigation District’s board approved seven agreements related to the U.S.-Mexico deal on Tuesday. The district holds the biggest single water entitlement along the Colorado River and supplies water to farms producing crops from alfalfa to Brussels sprouts.

IID Water Department Manager Tina Shields said there’s an interest on both sides of the border in “continuing the cooperative measures outlined in this agreement.”

“This allows for the continued operation of the river system as a basin partnership, and provides benefits to both countries’ water users by more specifically defining reservoir management strategies during this historic drought,” Shields said in a statement. “This leads to a higher level of operational certainty, particularly for lower basin water users that rely upon water deliveries released from Lake Mead.”

The agreement, which will remain in effect through 2026, lays out a strategy for Mexico and the U.S. states to jointly put the brakes on water use to reduce the risks of a crash in the system if the drought persists.

As of this week, Lake Mead stands at just 39% full, with its level at an elevation of 1,081 feet.

Under federal guidelines, the Interior Department would declare a shortage — which would trigger cutbacks for Arizona and Nevada — if Lake Mead’s level is projected to be below 1,075 feet as of the start of the following year.

Earlier this year, the Bureau of Reclamation estimated the odds of Lake Mead hitting shortage levels in 2019 at 31%. A previous projection had put the odds at 50-50 before last winter brought an above-average snowpack across the Rocky Mountains.

Follow Ian James on Twitter: @TDSIanJames

Source: https://www.usatoday.com/story/news/nation-now/2017/09/14/u-s-and-mexico-set-sign-landmark-colorado-river-water-sharing-deal/668596001/

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