T. Tibbitts<\/span><\/figcaption><\/figure>\nThat suggests our modern megadrought falls within the realm of natural variability, Evans says. What\u2019s different, she adds, is that it\u2019s a \u201cwarm drought.\u201d<\/p>\n
Temperature plays a key role in how much moisture remains on the ground as rain or snow. The hot conditions brought on by climate change, Anchukaitis says, have made the sponge of the atmosphere better at sucking up moisture. A 192-year-old thermodynamic formula called the Clausius-Clapeyron equation explains how: For each degree Celsius of warming, a parcel of air can hold 7 percent more water. \u201cA thirsty atmosphere will take that water that does fall from the sky away from the surface,\u201d Anchukaitis says.<\/p>\n
Those effects\u2009\u2014\u2009and the uncertainty over how long they will continue\u2009\u2014\u2009has caused some researchers to stop using the word \u201cdrought\u201d altogether. Instead, they favor the term \u201caridification,\u201d which describes a progressive drying process. Wet weather can come and go, Anchukaitis says, but if the temperature keeps rising, it\u2019s the perfect recipe for aridification.<\/p>\n
A Pacific influence<\/h2>\n An arid atmosphere isn\u2019t all that\u2019s driving the megadrought. The other piece of the puzzle lies in the vast waters of the Pacific Ocean.<\/p>\n
At its heart is a phenomenon known as the Pacific Decadal Oscillation, or PDO. It\u2019s an alternating climate pattern in which areas of warmer and cooler than normal surface waters switch their positions every 20 years or so, says climate scientist Richard Seager of Columbia University. Unlike some shorter-term climate patterns, the PDO \u201cgoes back and forth with timescales of many decades,\u201d Seager says.<\/p>\n
Scientists had long assumed that the PDO obeyed a regular rhythm dictated by the complex interactions between the land, sea and atmosphere. Understanding that cadence has always been of vital interest, Anchukaitis says, because of the PDO\u2019s powerful influence on the North American climate.<\/p>\n
When the PDO shifts, it diverts the path of the Pacific jet stream, a band of high-flying winds that steers weather patterns around the world. During the PDO\u2019s warm phase, a horseshoe of cooler water covers the northern, western and southern Pacific, while a warmer tongue occupies the eastern Pacific. That pushes the Pacific jet stream south over North America, shepherding wet weather patterns into the Southwest.<\/p>\n
But when the PDO switches to its cool phase, the locations of those warm and cool surface waters flip, and the jet stream moves north, diverting wet weather patterns out of the Southwest and making drought more likely.<\/p>\n
The PDO\u2019s last warm phase ran from 1977 to 1998, causing the wettest period the Southwest had seen in a millennium, Seager and colleagues reported in 2025 in AGU Advances<\/em>. But sometime around 1999, the needle swung in the other direction, moving the region from an extremely wet period to an exceptionally dry one, Seager says.<\/p>\nIn a cross section of wood taken from an old Douglas fir in Utah, a dark band of narrow and densely packed tree rings (indicated by the white arrow) records a prolonged period of dryness dating to the 12th century.<\/span>N. Ogasa<\/span><\/figcaption><\/figure>\nGiven the PDO\u2019s presumed cyclical nature, many scientists thought that the switch was only temporary. \u201cThe conventional wisdom suggested that the PDO could shift any given year, and we [wouldn\u2019t] have to worry about drought [after that],\u201d says climate scientist Jeremy Klavans of the University of Miami.<\/p>\n
But he and colleagues weren\u2019t so sure. They dug into that assumption, analyzing more than 500 simulations of the PDO from a dozen major climate models. They examined how the PDO shifted\u2009\u2014\u2009and stabilized\u2009\u2014\u2009in the presence of outside forces such as volcanic eruptions, solar variation and levels of greenhouse gases and aerosols.<\/p>\n
Their finding: Greenhouse gas and aerosol emissions had effectively hijacked the behavior of the PDO over the last 50 years by altering atmospheric temperatures, the team reported in 2025 in Nature<\/em>.<\/p>\nBallooning concentrations of industrial aerosols\u2009\u2014\u2009which can have an atmospheric cooling effect\u2009\u2014\u2009probably pushed the PDO to increasingly favor its warm phase starting in the 1950s, the researchers say. But in the 1980s, clean air legislation decreased aerosol emissions even as greenhouse gas levels continued to rise and warm the atmosphere. That combination drove the PDO toward its cool phase, making drought conditions more likely in the Southwest. Instead of being a rare event, drought \u201cbecomes kind of commonplace,\u201d Klavans says.<\/p>\n
To see if such events had historic precedent, another group of researchers looked to a period of warming that took place during the mid-Holocene Epoch, some 6,000 years ago. At the time, changes to Earth\u2019s orbit around the sun and the spread of vegetation caused less sunlight to be reflected away from the planet, heating up the Northern Hemisphere. The researchers reasoned such warming should have pushed the PDO into a prolonged cool phase.<\/p>\n
After scouring data from bog and lake sediment cores and analyzing dozens of climate simulations re-creating the period, they found that something resembling a cool phase of the PDO did in fact take place. It lasted several thousand years, during which time drought became widespread across the Southwest, they reported in 2025 in Nature Geoscience<\/em>.<\/p>\nAnd the current climate models may actually be underestimating the potential duration of the ongoing megadrought, based on those findings, says study coauthor Victoria Todd, a climate scientist at the National Center for Atmospheric Research in Boulder, Colo.<\/p>\n
That could be bad news for the American Southwest, Udall says. Even if people stopped emitting greenhouse gases today, planet-warming carbon dioxide will continue to accumulate in the atmosphere, locking the PDO and megadrought into place, potentially for decades. If the emerging science is right, then the Southwest is going to keep getting drier and drier, Udall says. \u201cNo question about it.\u201d<\/p>\n
Trading Places<\/h3>\n The Pacific Decadal Oscillation, or PDO, is a climate pattern in which areas of warmer- and cooler-than-normal surface waters in the Pacific Ocean switch their locations every couple of decades. This affects climate on the surrounding continents.<\/p>\n
Warm phase (1977\u20131998)<\/h4>\nT. Tibbitts<\/span>T. Tibbitts<\/span><\/figcaption><\/figure>\nDuring the PDO\u2019s warm phase, the Pacific jet stream (red arrow) moves south over North America, drawing wet weather patterns into the Southwest.<\/p>\n
Cool phase (1999\u2013now)<\/h4>\nT. Tibbitts<\/span>T. Tibbitts<\/span><\/figcaption><\/figure>\nWhen the PDO switches to its cool phase, the Pacific jet stream (blue arrow) moves north, diverting wet weather patterns out of the Southwest and making drought more likely.<\/p>\n
What\u2019s to come<\/h2>\n The hypothesis that human emissions have disrupted the PDO could be put to the test this year. That\u2019s because scientists are predicting a historically strong El Ni\u00f1o, a Pacific climate pattern characterized by months of warmer than normal sea surface temperatures in the eastern equatorial Pacific. El Ni\u00f1os often bring wet conditions to the Southwest\u2009\u2014\u2009and they have been known to force the PDO into a different phase. For example, the 1976\u20131977 El Ni\u00f1o helped push the PDO into a warm phase for nearly a quarter of a century.<\/p>\n
But a powerful El Ni\u00f1o in 2015 wasn\u2019t able to force the switch for more than a few years. That suggests the PDO may be slowly changing, Klavans says. \u201cSomething\u2019s different here.\u201d<\/p>\n
Even if the current El Ni\u00f1o is strong enough to force the PDO into a warm phase, no one should expect the megadrought to go away any time soon, Seager says. \u201cWe\u2019re talking about something that\u2019s been going on for a few decades now. Even one very wet winter is not going to be enough to restore Colorado River reservoirs to where they would preferably be.\u201d<\/p>\n
To find out what would happen if the PDO switched to a warm phase in the near future, Seager and colleagues simulated multiple scenarios in which the PDO either stayed in the warm phase or flipped back into a cool phase, all the while monitoring potential impacts on the megadrought.<\/p>\n
Even in the best-case scenarios, the Southwest never returns to the wet years of the 1980s and \u201990s, when lakes Powell and Mead reached maximum capacity numerous times, the researchers reported in 2023 in npj Climate and Atmospheric Science<\/em>. The findings instead suggest that, regardless of what the PDO does, the region will face a far drier climate than it did in its recent past. In other words, even if the megadrought were to end, the Southwest faces an uncertain future when it comes to water, according to the study.<\/p>\nCommunities need to prepare for the future by improving their water conservation efforts and infrastructure, Anchukaitis says. Those practices will grow only more crucial as the Southwest\u2019s population continues to balloon: Utah, Texas, Nevada, Colorado and Arizona are among the 10 fastest growing states by population this decade, according to a 2024 report by the University of Virginia\u2019s Weldon Cooper Center for Public Service.<\/p>\n
Even if wet weather returns, Anchukaitis says, the cities of the Southwest shouldn\u2019t fall into complacency. \u201c[More rain] doesn\u2019t mean that\u2009\u2026\u2009megadroughts aren\u2019t going to come back,\u201d he says. \u201cMaybe it buys us some time to ease systems into a new way of thinking.\u201d<\/p>\n
In Kearny, the town\u2019s residents have made some impactful changes. Though officials first warned Zero Day could occur in July, they now estimate that water restrictions and conservation efforts\u2009\u2014\u2009as well as canceled water requests by other communities\u2009\u2014\u2009have helped extend the town\u2019s water supply until at least the end of the year.<\/p>\nAfter being told their community could run out of water within months, residents in Kearny, Ariz. cut back on their usage and helped extend the town\u2019s supply to the end of the year.<\/span>N. Ogasa<\/span><\/figcaption><\/figure>\nBut such measures can do only so much. The upstream flow of the Gila River is controlled by the Coolidge Dam, and the reservoir behind the dam is currently less than 1 percent full. If nothing changes before next year, Kearny\u2019s annual allotment of river water could fall to zero.<\/p>\n
Back in his store, Warren contemplates the town\u2019s future. \u201cThis is going to hurt us if we have to shut off our livelihood,\u201d he says, glancing around at his stocked shelves. \u201cWe can\u2019t walk away from it.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"
Kearny, Ariz., is a town on the brink. Located at the foot of the Dripping Spring Mountains in eastern Arizona, this small community of 2,000 people sources its water from the Gila River, a verdant waterway that snakes by the southern edge of town. But in March, the snowpack feeding the river had dropped to […]<\/p>\n","protected":false},"author":1,"featured_media":105983,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":[],"categories":[10],"tags":[],"_links":{"self":[{"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=\/wp\/v2\/posts\/105982"}],"collection":[{"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=105982"}],"version-history":[{"count":0,"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=\/wp\/v2\/posts\/105982\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=\/wp\/v2\/media\/105983"}],"wp:attachment":[{"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=105982"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=105982"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.adviews.info\/news\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=105982"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}