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8th Century Megadrought Impacted Much of North America

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    NHNE News List Current Members: 724 Subscribe/unsubscribe/archive info at the bottom of this message. ... EIGHTH CENTURY MEGADROUGHT IMPACTED MUCH OF NORTH
    Message 1 of 1 , Nov 4, 2002
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      University of Arkansas / Newswise
      October 31, 2002


      FAYETTEVILLE, Ark. -- A drought that lasted three times as long as the Dust
      Bowl of the 1930s wreaked ecological havoc over much of the western United
      States and Mexico, and occurred at about the same time as the fall of
      Teotihuacan and classic Mayan civilization 13 centuries ago, say University
      of Arkansas researchers.

      David Stahle, professor of geosciences, presented some of his findings today
      at the annual Council for the Advancement of Science Writing meeting in St.
      Louis, Mo.

      "The megadrought of the eighth century was three times longer than the Dust
      Bowl," Stahle said. "The consequences, ecologically and socially, must have
      been enormous."

      Stahle and colleagues at the University of Arkansas (Matthew Therrell,
      Malcolm Cleaveland, and Falko Fye), the National University in Mexico City
      (Rodolfo Acuna-Soto), the University of Tennessee (Henri Grissino-Mayer),
      and Columbia University's Lamont-Doherty Earth Observatory (Edward Cook)
      have compiled tree ring and lake sediment records to study prolonged
      multi-decadal drought over the past 2,000 years.

      The tree-ring data indicate a severe drought in the eighth century that
      lasted from AD 736 to 765, a period of 30 years. Rainfall over New Mexico
      averaged only 90 percent of normal for this entire 30-year period and only
      83 percent of normal during the worst decade of the eighth century
      "megadrought." In Nebraska, during the heart of the Dust Bowl drought of the
      1930s, annual rainfall averaged just 80 percent of normal. A single year
      with only 80 percent of normal rainfall constitutes a serious deficit, but
      decadal or multi-decadal dry spells of this magnitude can have catastrophic
      environmental and social consequences, as witnessed during the Dust Bowl.

      Widespread, intense droughts like the eighth century event can impact the
      ecology of a region. Long term drought conditions affect a region's plant
      life, animal life and hydrology and have been linked historically to
      outbreaks of disease.

      "They leave behind a big footprint," Stahle said. Indeed, Stahle and his
      colleagues have shown evidence in the tree-ring record of another
      continental-scale megadrought that occurred in the 16th century. The 16th
      century drought conditions lasted 40 to 50 years, probably the most serious
      drought in the last 2000 years over North America, a megadrought that
      certainly affected the first European settlements in North America. The 16th
      century drought seems to have contributed to the virulence of hemorrhagic
      fever outbreaks that swept through the native populations in Mexico in 1545
      and 1576 and caused the deaths of millions of people.

      The tree-ring chronologies document eighth century megadrought over the
      southwestern United States, but lake sediment records indicate that this
      severe drought may have extended into the northern Great Plains and across
      central Mexico, possibly including the Yucatan peninsula. Severe drought has
      been well documented over central Mexico and the Yucatan during the late
      first millennium AD, and the new tree-ring data suggest that this period of
      prolonged drought may have begun in the middle of the eighth century over
      the southwestern United States and northern Mexico.

      The lake sediment records of epic drought in the Yucatan have been linked to
      the collapse of classic Mayan culture. And the new research indicates that
      the eighth century drought may have also contributed to the decline of
      Teotihuacan in central Mexico, one of the six largest cities in the world at
      the time.

      "Any society would be stressed under the conditions of one of these
      megadroughts," said Stahle. "And we now believe that prolonged drought may
      have been a factor in the collapse of Teotihuacan."


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