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From Record Floods to Drought in Three Months: Unusually Hot, Dry Conditions Blanket South

Back during late August of 2017, Hurricane Harvey dumped as much as 60.48 inches of rain over southeast Texas. Harvey was the wettest tropical cyclone on record ever to strike the U.S. — burying Houston and the surrounding region under multiple feet of water, resulting in the loss of 91 souls, and inflicting more than 198 billion dollars in damages.

Harvey was the costliest natural disaster ever to strike the U.S. Its tropical rains were the heaviest ever seen since we started keeping a record. But strangely, almost inexplicably, just a little more than three months later, the region of southeast Texas is now facing moderate drought conditions.

(Just three months after Harvey’s record rains, Southeast Texas is experiencing drought. No, this is not quite normal despite a mild La Nina exerting a drying influence. Image source: U.S. Drought Monitor. Hat tip to Eric Holthaus.)

How did this happen? How did so much water disappear so soon? How could an instance of one of the most severe floods due to rainfall the U.S. has ever experienced turn so hard back to drought in so short a time?

In a sentence — climate change appears to be amplifying a natural switch to warmer, drier weather conditions associated with La Nina.

Climate change, by adding heat to the Earth’s atmosphere and oceans fundamentally changes the flow of moisture between the air, the ocean and the land. It increases the intensity of both evaporation and precipitation. But this increase isn’t even. It is more likely to come about in extreme events. In other words, climate change increases the likelihood of both more extreme drought and more extreme rainfall.

Of course, climate change does not exist in a vacuum. Base weather and climate conditions influence climate change’s impact. At present, with La Nina emerging in the Pacific, the tendency for the southern U.S. would be to experience warmer and drier conditions. But in a normal climate, these conditions would tend to be milder. In the present climate — warmed up by fossil fuel burning — the tendency is, moreso, to turn toward an extreme. In this case, an extreme on the hot and dry end of the climate spectrum.

For the region of Southeast Texas flooded so recently by Harvey’s record rains, it means that a turn from far too wet to rather too dry took just a little more than 3 months.

(Both temperature and moisture took a very hard turn over the past 30 days. Such extremely warm and dry conditions increase the likelihood of flash drought. A climate feature that has become far more frequent as the Earth has warmed. Image source: NOAA.)

South Texas, however, is just one pin in the map of a larger trend toward drought that is now blanketing the South. Over the past month, precipitation levels were less than 50 percent of normal amounts in most locations with a broad region over the south and west experiencing less than 10 percent of the normal allotment of moisture. Meanwhile, 90-day precipitation averages are also much lower than normal across the South.

Precipitation is a primary factor determining drought. But temperature can mitigate or worsen drought conditions. Higher temperatures cause swifter evaporation — driving moisture out of soils at a faster rate. And average temperatures across the south have been quite warm recently. With one month averages ranging from 1 C above normal over most of the south to a whopping 8 C above normal over parts of New Mexico. As with lower than normal precipitation, higher than normal temperatures have also extended into the past 90 day period across most of the South.

 

(Moderate drought conditions are widespread as severe to extreme drought is starting to crop up in the South-Central U.S. With La Nina likely to continue through winter and with global temperatures in the range of 1.1 to 1.2 C above pre-industrial averages, there is risk that conditions will intensify. Image source: U.S. Drought Monitor.)

The upshot is that moderate drought is taking hold, not just in southeast Texas, but across the southwest, the southeast, and south-central U.S. Severe to extreme drought has also already blossomed from northern Texas and Louisiana through Oklahoma, Arkansas and Missouri. This is relatively early to see such a sharp turn, especially considering the fact that La Nina conditions have only lasted for a short while and have, so far, been rather mild on the scale of that particular climate event.

Furthermore, like Texas, many of these drying regions experienced extreme rainfall events during spring and summer. Such events, however, were not enough to stave off a hard shift to drought in a world in which human-caused climate change is now driving both droughts and more extreme rainfall events to rising intensity.

(Predicted temperature and precipitation variance from normal over next three months. Climate change is likely to enhance this variability related feature. Image source: NOAA.)

With La Nina likely to remain in place throughout winter, the typical climate tendency would be for continued above average temperatures across the south and continued below average rainfall for the same region. Present human-caused global warming through fossil fuel burning in the range of 1.1 to 1.2 C above pre-industrial averages will tend to continue to amplify this warm, dry end of the natural variability cycle (for the southern U.S.).

In other words, there is not insignificant risk that the hard turn away from record wet conditions in the South will continue and that severe to very severe drought conditions will tend to spring up and expand.

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22 Comments

  1. Erik Frederiksen

     /  December 4, 2017

    Thanks for the article. Last year in an interview in the Guardian James Hansen said something interesting about increases in extreme weather.

    “Some things do change gradually because of the inertia system. The global average temperature, if you average it over several years, is going up pretty smoothly, since the middle 1970s. January/February of this year, global temperature is now 1.3 degrees above the 1950-1980 average, but that was just two months. Averaged over the year, it’s going to be about 0.9 degrees Celsius, and that’s pretty much on this almost linear increase over the last four decades.

    Locally and regionally you get abrupt events, which are the ones that have the biggest impact on people. The frequency and severity of extreme events increase as the planet continues to get warmer. Sea level and ice-sheet disintegration is also a very nonlinear process. It’s going to lead to rapid change within the next several decades.”

    https://www.theguardian.com/environment/2016/apr/12/climate-scientist-james-hansen-i-dont-think-im-an-alarmist

    Reply
    • Sheri

       /  December 4, 2017

      Phoenix has had n o rain since the end of August. Yes this is VERY unusual and is beginning to feel very alarming to me. The weather that should have cooled us down first in November didnt’ get here until the past few days, and even then it is still very very warm. We “usually” get storms and rain end of September through winter rains through say, February. Our driest season is more like spring to early summer not fall and winter. Monsoon weather starts in JUly and runs to Sept.

      Actually, the past 4-5 years we’ve gotten very little in the way of winter rains anyway. It is noticeable not just my childhood, 50 yrs ago, but fro even 10 yrs ago. About 5 yrs something seemed to really change in our seasons, yes we do have seasons here, Since then, our “seasonal” weather has had some big ,um, the word I want is , anomalies.

      The whole thing is personally very distressing and is to several of my friends. It has made a difficult year for me somehow even more depressing.

      This dryness goes for our whole state and S. California , New Mexico and probably Nevada.
      Thanks for this report, Robert as with all your work.

      Reply
      • :(. Not fun.

        Long term drying trend driven by warming. This particular dry patch is being enhanced by La Nina. But we wouldn’t be seeing these kinds of extremes under a normal La Nina in a normal climate.

        Reply
      • coloradobob

         /  December 4, 2017

        ALBUQUERQUE, N.M. (KRQE) – After logging high temperatures way above seasonal average, Albuquerque shattered heat records for November.

        The National Weather Service released data Friday saying temperature records were typically broken by one-tenth or two, but that wasn’t the case this year.

        The warmest November on record resulted in an average temperature of 52.8 beating the 51 degree marked more than a century ago in 1909.

        http://krqe.com/blog/2017/12/01/nws-albuquerque-shatters-november-heat-records/

        Reply
        • coloradobob

           /  December 4, 2017

          ovember joined the ranks in 2017 as among the warmest months on record, with Tucson’s temperature averaging about 4 degrees above normal.

          This year could end up as the warmest ever.

          “We had quite a few days with temperatures we don’t usually see during the month of November. We had some highs in the 90s, quite a few 80s,” said National Weather Service meteorologist Dan Leins.

          Earlier in the year, March and June also set all-time-high average temperature records.

          https://news.azpm.org/p/news-articles/2017/12/4/120746-november-sets-tucson-heat-record/

        • Wow. Reminds me of recent records broken this Summer during the California heat wave. The records just got left behind in the dust.

      • coloradobob

         /  December 4, 2017

        Phoenix weather: We just had the hottest November ever. And 2017 could be the city’s hottest year
        Warmest November

        Next let’s take a look at what happened in November.

        A persistent area of high pressure hovered over the state and kept temperatures above normal throughout the month.

        • The average high for the month was 82.9 degrees, the warmest ever and 7.4 degrees above normal for that statistic. The previous record was 82.3 degrees in November 1949.

        https://www.azcentral.com/story/news/local/phoenix-weather/2017/12/01/phoenix-weather-hottest-november-ever/910586001/

        Reply
  2. Allan Barr

     /  December 4, 2017

    Most of the United States is going to end up being a dust bowl, according to climate projections, wonder what we here are going to eat with the oglala projected to dry up in the next decade or so and major issues with the california aquifer. Food and water the basics of life are going to become major issues I imagine.

    Reply
    • Apneaman

       /  December 4, 2017

      Allan, y’all will be heading up here to Canada for Manifest Destiny 2.0

      Reply
  3. coloradobob

     /  December 4, 2017

    Reply
    • Thanks for this, Bob. Kinda on a similar line of thought right now. Winter may be coming for the Eastern U.S. But for Alaska, not so much.

      Reply
    • rhymeswithgoalie

       /  December 4, 2017

      Crap. Does that mean that GFS is going to need to extend their temperature legend again?

      Reply
  4. coloradobob

     /  December 4, 2017

    Trump closes panel meant to help cities deal with climate change

    The Trump administration is disbanding an interagency panel that was created to help cities deal with the effects of climate change.

    Jesse Keenan, a Harvard University professor specializing in climate adaptation and chairman of the panel, told members at a Monday meeting that it would be their last, Bloomberg News reported.

    “It was one of the last federal bodies that openly talked about climate change in public,” Keenan told Bloomberg. “I can say that we tried our best and we never self-censored!”

    http://thehill.com/policy/energy-environment/363143-trump-closes-panel-meant-to-help-cities-deal-with-climate-change

    Reply
    • Erik Frederiksen

       /  December 4, 2017

      Here’s an article about Alaskan towns and cities threatened by global warming impacts and the lack of help they are getting from the government. From the NY Times November 2016. Note, the cost to move one village of around 600 people will cost an estimated $180 million.

      “The government has identified at least 31 Alaskan towns and cities at imminent risk of destruction . . .

      At least two villages farther up the western coast, Shishmaref and Kivalina, have voted to relocate when and if they can find a suitable site and the money to do so. A third, Newtok, in the soggy Yukon-Kuskokwim Delta farther south, has taken the first steps toward a move.

      But, after years of meetings that led nowhere and pleas for government financing that remained unmet, Shaktoolik has decided it will “stay and defend,” at least for the time being, the mayor, Eugene Asicksik, said.

      “We are doing things on our own,” he said.”

      If the government won’t appropriate the funds to move a few dozen small cities and towns, what will they do about the 1,400 cities and towns in the US threatened by sea level rise like Houston, New Orleans, Miami, NYC and Boston?

      We’ll all be “doing things on our own.”

      Reply
  5. coloradobob

     /  December 4, 2017

    This chart for 2017 (Alaska NWS) shows the heat and the current spike in December; but notice the heat spikes just about year round in terms of the whole year (observed)

    Reply
  6. coloradobob

     /  December 4, 2017

    Took a look at the numbers for Fairbanks ………..
    Almanac for December 4, 2017

    FORECAST AVERAGE *RANGE *
    Temperature
    High 26 °F 1 °F -29 to 10 °F
    Low 16 °F -6 °F -40 to -11 °F

    https://www.wunderground.com/weather/us/ak/fairbanks/99701

    Reply
  7. coloradobob

     /  December 4, 2017

    Global warming to claim 33% of ice volume in Hindu Kush Himalayan region: Expert

    KATHMANDU: Global warming is not only posing a serious threat to glaciers, it will also result in a loss of 33 per cent of total ice volume in the Hindu Kush Himalayan (HKH) region by the end of the century, leading dire consequences for people living there.

    Read more at:
    //economictimes.indiatimes.com/articleshow/61918393.cms?utm_source=contentofinterest&utm_medium=text&utm_campaign=cppst

    Reply
  8. Kiwi Griff

     /  December 6, 2017

    Hi all I know some from other blogs.

    NZ is having the same extremes.

    We have gone from extreme rain to drought in a couple of months.

    http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11925217
    Record rainfall: 2017 – ‘The year it didn’t stop raining’
    In a year of extreme rainfall amounts, a MetService meteorologist is describing 2017 as “the year it didn’t stop raining”.
    Waikato and Bay of Plenty rainfall are already at record levels, and extreme rainfall levels are being recorded across the north and east of the North Island, and along the eastern South Island.
    22 Sep, 2017 12:38pm

    Followed by.

    https://www.radionz.co.nz/news/environment/345137/drought-risk-rises-with-dramatic-shortage-of-rain
    1 Dec 2017
    Drought risk rises with ‘dramatic shortage of rain’
    5:52 am on 1 December 2017
    The risk of drought is rising as soils saturated after a deluge of rain winter and early spring rapidly dry out.

    Reply

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