U.S. southwest could see a 60-year drought like that of 12th century — only hotter — this century

An unprecedented combination of heat plus decades of drought could be in store for the Southwest sometime this century, suggests new research from a University of Arizona-led team….

“The bottom line is, we could have a Medieval-style drought with even warmer temperatures,” [lead author Connie] Woodhouse said.

In 2007, Science (subs. req’d) published research that “predicted a permanent drought by 2050 throughout the Southwest” “” levels of aridity comparable to the 1930s Dust Bowl would stretch from Kansas to California.

In October, a National Center for Atmospheric Research (NCAR) study warned, “The United States and many other heavily populated countries face a growing threat of severe and prolonged drought in coming decadespossibly reaching a scale in some regions by the end of the century that has rarely, if ever, been observed in modern times.

UPDATE:  A new Environmental Research Letters article, “Characterizing changes in drought risk for the United States from climate change,” comes to a similar conclusion as the NCAR study, “Drought frequencies and uncertainties in their projection tend to increase considerably over time and show a strong worsening trend along higher greenhouse gas emissions scenarios, suggesting substantial benefits for greenhouse gas emissions reductions.”  See especially Figure 4C.

Now a new Proceedings of the National Academy of Sciences study, “A 1,200-year perspective of 21st century drought in southwestern North America” looks at the paleoclimate record to see the kind of drought the southwest — and other regions — might experience.  It concludes:

Instrumental records and paleoclimatic evidence for past prolonged drought in the Southwest that coincide with elevated temperatures can be assessed to provide insights on temperature- drought relations and to develop worst-case scenarios for the future. In particular, during the medieval period, ˆ¼AD 900- 1300, the Northern Hemisphere experienced temperatures warmer than all but the most recent decades. Paleoclimatic and model data indicate increased temperatures in western North America of approximately 1 °C over the long-term mean. This was a period of extensive and persistent aridity over western North America. Paleoclimatic evidence suggests drought in the mid-12th century far exceeded the severity, duration, and extent of subsequent droughts. The driest decade of this drought was anomalously warm, though not as warm as the late 20th and early 21st centuries. The convergence of prolonged warming and arid conditions suggests the mid-12th century may serve as a conservative analogue for severe droughts that might occur in the future. The severity, extent, and persistence of the 12th century drought that occurred under natural climate variability, have important implications for water resource management. The causes of past and future drought will not be identical but warm droughts, inferred from paleoclimatic records, demonstrate the plausibility of extensive, severe droughts, provide a long-term perspective on the ongoing drought conditions in the Southwest, and suggest the need for regional sustainability planning for the future.

Future droughts will be fundamentally different from all previous droughts that humanity has experienced because they will be very hot weather droughts, as I have written (see Must-have PPT: The “global-change-type drought” and the future of extreme weather).

The University of Arizona news release makes a similar point:

Droughts that are accompanied by warm temperatures have more severe impacts on ecosystems, said Meko, an associate research professor in the UA’s Laboratory of Tree-Ring Research.

During the Medieval period, temperatures were about 1.8 degrees Fahrenheit (1 C) above the long-term average.  Average temperatures in the Southwest have been warmer than that since 1990 and are projected to increase at least another 3.6 F (2 C) by 2100, Woodhouse said.

Well, holding at 2C warming for the SW requires the world to take action immediately and stay below 450 ppm.  Not bloody likely at this point.  On our current emissions path, the SW is facing 6C (11F) warming or more.

The most severe warm-climate drought in the Southwest within the last 1,200 years was 60 years long and occurred during the mid-12th century, according to research by Meko and others. That drought covered most of the western U.S. and northern Mexico.

For a 25-year period during that drought, Colorado River flow averaged 15 percent below normal, according to the tree-ring-based reconstruction of stream flow at Lees Ferry.

For every 1.8 degree Fahrenheit (1 C) of warming in the future, Colorado River flow is projected to decrease between two and eight percent, Woodhouse and her co-authors wrote.

Thus, in the worst-case, the Colorado River flow could drop by half by 2100.

The Colorado River supplies water for cities and agriculture in seven western states in the U.S. and two states in northwestern Mexico. Los Angeles, Las Vegas, Denver, Phoenix, Tucson and Albuquerque are among the many cities dependent on Colorado River water.

“Even without warming, if you had one of those medieval droughts now, the impact would be devastating,” she said. “Our water systems are not built to sustain us through that length of drought.”

… In recent decades, temperatures have been higher than during the previous 1,200 years, and future temperatures are predicted to be even warmer, Woodhouse said.In addition, other research predicts that changes in atmospheric circulation will reduce the amount of winter precipitation the Southwest receives in the future, she said.

“The bottom line is, we could have a Medieval-style drought with even warmer temperatures,” Woodhouse said.

Can’t say we weren’t warned.

Moreover, unlike medieval times, things will just get worse and worse for a long, long time — see NOAA stunner: Climate change “largely irreversible for 1000 years,” with permanent Dust Bowls in Southwest and around the globe.

The NCAR study makes clear what other regions face Dust-Bowlification (click figure to enlarge):

  • Much of Latin America, including large sections of Mexico and Brazil
  • Regions bordering the Mediterranean Sea, which could become especially dry
  • Large parts of Southwest Asia
  • Most of Africa and Australia, with particularly dry conditions in regions of Africa
  • Southeast Asia, including parts of China and neighboring countries

drought map 3 2060-2069

The maps use a common measure, the Palmer Drought Severity Index, which assigns positive numbers when conditions are unusually wet for a particular region, and negative numbers when conditions are unusually dry. A reading of -4 or below is considered extreme drought….

There are also uncertainties in how well the Palmer index captures the range of conditions that future climate may produce. The index could be overestimating drought intensity in the more extreme cases, says Dai. On the other hand, the index may be underestimating the loss of soil moisture should rain and snow fall in shorter, heavier bursts and run off more quickly. Such precipitation trends have already been diagnosed in the United States and several other areas over recent years, says Dai.

The PDSI in the Great Plains during the Dust Bowl apparently spiked very briefly to -6, but otherwise rarely exceeded -3 for the decade (see here).  So the numbers projected by NCAR are beyond catastrophic by the 2060s.  By the 2090s, the damage would be unimaginable, as NCAR explained:

By the end of the century, many populated areas, including parts of the United States, could face readings in the range of -8 to -10, and much of the Mediterranean could fall to -15 to -20. Such readings would be almost unprecedented.

drought map 4 2090-2099

Note that the devastation extends far beyond what is considered the Southwest United States, with staggering drought indices right in the middle of the breadbasket.

This is, of course, just one of many devastating impact the nation and the world face on our current path of unrestricted greenhouse gas emissions (see “A stunning year in climate science reveals that human civilization is on the precipice” and “Royal Society special issue details ‘hellish vision’ of 7°F (4°C) world — which we may face in the 2060s!

While it seems politically implausible that we are going to take serious action anytime soon, that doesn’t mean our inaction is any less immoral.  People need to understand what we risk if we stay anywhere near our current emissions path — if only so they can plan ahead based on the best available information we have.  But the time for rapid deployment of every available low-carbon technology is still right now.
For a glimpse of what’s coming to the United States, look to Australia, the most arid habited continental, the canary in coal mine for climate change:

25 Responses to U.S. southwest could see a 60-year drought like that of 12th century — only hotter — this century

  1. Solar Jim says:

    There are no limits to arrogance and greed so we witness the coming collapse of grain crops and our entire nation so we can make mining corporations and their banksters richer. The clear and present danger to national security are ourselves and our chosen governance by wealth and the politically connected (i.e. paid lobbyists).

    These continuing reports are overwhelming, yet we stand immobile and corrupted by the very concepts of “energy” and “governance.”

  2. Lou Grinzo says:

    Once again: The primary vector for the human impacts of climate change will be water. Rising seas, increased storms and storm surges, heavier rain and snow events, and the biggest one of them all, droughts.

  3. Brendan says:

    Could you give us some basic science on how it could be drier everywhere in the world except Alaska? Seems to imply that it will stop raining everywhere and all the water will go into the oceans. At the same time, you’ve mentioned in other parts of the blog how hotter water means more evaporation means bigger rainstorms (in certain places)

  4. Peter M says:

    The inland ‘heart’ of the USA, from the projections seen on the map, look very hot and dry. It seems dust-bowl conditions could exists from Indiana west to the front range of the Rockies, and from the Dakota’s south ti the Rio Grande.

    There will likely be a complete disappearance of agriculture by 2050- and all farming by the end of the century.

    Madness? yes- it seems that the USA will exist as a fragmented nation climatically- a strip on the west coast from San Francisco to Vancouver the upper great lakes, and Central to northern New England (those areas not flooded)

    The rest? Areas not flooded- hot and dry as well. Punctuated by extreme violent storms and tropical cyclones.

  5. Ominous Clouds Overhead says:

    Glad I sold my house in Moab, Utah.

    I’ve already seen the impacts of global warming on that region on a daily basis for the past 20 years. It’s heartbreaking watching the habitat become more and more inhospitable for its animal and bird residents.

    And of course, for us humans, too, though most seem too myopic to really notice. I’ve watched the desertification for a long time, and it looks to get much much worse. Most of the cities in the desert SW will dry up and blow away. I won’t be sad to see vegas blow to the nether regions.

  6. Jon says:


    Ummm… not to say it’s a bad question in principle but surely you mean except Alaska, almost everywhere else north of 60, quite a lot of eastern Africa, India, a fair bit of northern China, Uruguay and neighbouring chunks of Argentina and Brazil, Papua-New Guinea, and so on with smaller areas of projected increased wetness than the ones just listed?

  7. Stefan says:

    A Palmer index of -15 to -20 seems beyond comprehension. Much of southern Europe may turn into a desert, and even parts of western and central Europe may become arid steppes.

  8. paulm says:

    “The planned complex is precisely the type of facility the Obama administration was imagining when it put those rules in place.

    It would roughly double South Dakota’s carbon footprint, producing an estimated 16.9 million tons of carbon dioxide each year, and if it were a country of its own, it would rank 85th worldwide in greenhouse gas emissions, just behind the Dominican Republic and Estonia.”

  9. Harold Pierce Jr says:

    What happens to cloud formation and rainfall over the oceans? If the climate warms up, there would be more clouds and moisture in the air and where do they go? These are blown out of the oceans into the land because hot air rising from the land will be replaced by cooler moist air from the oceans, a process known as “sea breeze”.

    In 2090, the PDO will be in cool phase so the projected drought my not be as severe as projected. In 1910 the PDO went into a warm phase, the result of which was the drought in the 1930’s.

    The PDO has cycle time of ca 60 years which is comprised of warm and cool phases which are 30 years for each.

    BTW, If you want water, come to super-natursl, beatiful British Columbia, the Best Place on Earth. Many meters of rain fall in the coastal temperate rain forests. And there will always be water in the Fraser river.

  10. paulm says:

    So caribbean islands think the frequency of hurricanes are increasing….

    ‘We are not having the increase in the number of hurricanes because God has chosen to be unhappy with us. It is because of what has been done to the global climate.

  11. Rabid Doomsayer says:

    And this planet will support 9 bilion people, I don’t think so.

  12. Ominous Clouds Overhead says:

    Harold Pierce Jr #9

    Was there last summer and the mosquitos about drove me crazy. Beautiful, though.

  13. Barry says:

    Global warming can easily deliver both more precipitation and more drought in the same location.

    Here are a few ways:

    — “rain and snow fall in shorter, heavier bursts and run off more quickly.”

    — shifting rainfall to wet season and less in dry season. more rain falls when soils saturated so more runs off.

    — more snowfall but earlier melt. again more runs off when soils saturated.

    — warming air also increases absorption of soil moisture.

    Take the California Sierras. Moist ocean air dumps rain and snow as it rises and cools over the mountain chain. Like squeezing out a sponge. As the air falls down the other side it warms up and sucks soil moisture from the eastern slope soils. Like a squeezed sponge expanding over a wet counter. Global warming is creating a thicker sponge allowing even more soil moisture to be sucked up.

    Even before global warming created a thicker sponge, there are regions on earth that had “negative rainfall” from this effect. The rain/snow that falls each year is less than the evaporation-suck of the warm dry air the rest of the year. This could easily get worse with a bigger sponge.

  14. riverat says:


    As Jon pointed out it’s only going to get dryer on about half the land area. 3/4’s of the planet is covered by oceans and we don’t measure drought over them. Since there is little land below 60S latitude any increase in precipitation there wouldn’t show up.

    Also, I believe the Palmer Drought Severity Index is relative to what is considered normal for the area it is indexing. If the rainfall fell from 40″ to 20″ here in Oregon it would be a more severe drought than if it fell from 10″ to 7″ in Phoenix (numbers made up for the example).

  15. Now that we’ve added our bit, the saying ‘if you don’t like the weather, wait an hour’ can be rephrased as ‘if you don’t like the climate, wait a decade’.

  16. BBHY says:

    Absolute devastation, not the dustbowl but more like a North American Sahara.

    Interesting that the Sahara is forecast to have increased rainfall, returning to the dry savannah is was thousands of year ago.

  17. A face in the clouds says:

    There is a legal case worth watching in Galveston, Texas, which could affect property losses due to climate change if it goes beyond the state supreme court. The supreme court is being asked to reconsider a recent ruling which in effect halted an ambitious project to rebuild a large section of Galveston beaches lost to erosion (especially in the aftermath of Hurricane Ike). Public access is the cause being trumpeted by state officials who asked the supreme court for reconsideration, but easement is at issue too.

    Big, out-of-state money has also popped up in the middle of this squabble, causing some to speculate that it’s headed toward the federal courts. I wouldn’t know. Here in the state capital one can’t throw a rock without hitting a lawyer, meaning I’ll have to wait and read about it in the papers like the other mammals. However, non-lawyers like me do wonder if the state supreme court has simply thrown in the towel on trying to save Galveston from climate change.

  18. Roger Gram says:

    “…regional sustainability planning…”
    Would this be a pipeline taking water from Lake Superior to Los Vegas, or would it be more on the order of setting up refugee camps in northern Maine?

  19. DaveE says:

    Wasn’t this drought implicated in the collapse of Anasazi society? Something to look forward to.

  20. Jim says:

    Get out your copy of Cadillac Desert. It’s time to dust off those plans to divert the Fraser River from BC and feed that water into the Colorado where it belongs.

    (Map color coding is idiotic; driest and wettest are nearly identical colors on my screen.)

  21. DaveE says:

    #3 Brendon–being drier doesn’t necessarily mean no rain. As it says in the article, there may be periods of intense rain that run off quickly, but the higher temperatures then dry the soil out more quickly after any rains, leading to low soil moisture and continued drought.

  22. Colorado Bob says:

    DaveE @ 19 –

    When the 4 corners were first investigated by archeologists , where was common theme reported , “It looks like they all just got up and left.” There is one area there, that still remains like they left it. There are ruins on the Southern Ute Res. , much like the ones at Mesa Verde’ to the north. Pots, & corn cobs laying everywhere. The Utes never tidied things up, and never touched any of it. I’ve been to many of the other ruins in the area.
    After decades of progressively growing drier, 1276 was a very bad year in the area, that’s when the drought really took hold. It didn’t rain for the next 25 to 30 years.

    The Utes conduct horse back tours to these ruins.

  23. Ominous Clouds Overhead says:

    Look for lots more flashfloods in the deserts of the SW. A lot of the arroyos and such that used to contain these won’t be able to hold the higher amounts of rain. Warning to those who live near such and on low ground, esp. in places like Las Vegas and Phx.

  24. Harold Pierce Jr says:

    OCO at 14

    Metro Vancouver’s best kept secret: No mosquitos in the summer time!

    There are many places in BC where mosquitos, blackflies and punkies are so thick the sky turns black. However, in the dry interior in southern BC and in the Okanogan or on the Pacific coast, there are few if any of these vicious blood suckers.

    Osoyoos in semi-arid region and not a true desert, but we call it a pocket desert and this draws in the tourists who come to check out the wineries retirement and vacation properties. They are amazed to see saqe brush and marmots.

  25. PuppetKing says:

    We are witnessing the beginning of the end of Vegas and Phoenix. Utter collapse and ruin. Complete destruction and Detroitisation of these cities. Global warming and dwindling water supplies will only hasten the demise.
    The theory that lets build endlessly and they will come buy it, is nonsense…a part of voodoo economics spewed by American economists and professors (paid slaves of the American system).
    The system is going to come crashing down like a house of cards. Stunning ruins of Vegas and Phoenix will be all that remains of a bygone empire that future generations will witness and visit in complete shock and awe.
    So much so for the American southwest.