November 9, 2011
PHOENIX — A University of Arizona study says megadroughts — multi-decade periods of drought — may be a recurring feature of the Southwest's climate.
The study to be published in the journal Geophysical Research Letters revealed a previously unknown decades-long drought period in the second century for the region and suggests the area may have experienced more extended periods of aridity than originally believed.
University of Arizona geoscientists collected data for the study from the southern San Juan Mountains in south-central Colorado. The region serves as a primary drainage site for the Rio Grande and San Juan rivers.
"These mountains are very important for both the San Juan River and the Rio Grande River," said Cody Routson, a doctoral candidate in the environmental studies laboratory of the UA's department of geosciences and the primary author of the study. "We wanted to develop as long a record as possible for that region."
The geoscientists said the San Juan River is a tributary for the Colorado River, meaning any climate changes that affect the San Juan drainage also likely would affect the Colorado River and its watershed.
Scientists say the prolonged drought in the 12th century and the newly discovered event in the second century may both have been influenced by warmer-than-average Northern Hemisphere temperatures. The researchers looked for indications of climate in the past in the growth rings of the oldest trees in the southern San Juan region to develop their chronology.
The chronology extends many years earlier than the medieval period, during which two major drought events in that region already were known from previous chronologies.
Scientists have long known about the medieval drought, but never knew whether it was unique, Columbia University climate researcher Richard Seager told the Albuquerque Journal (http://bit.ly/v27qDr). Routson's data shows it was not, Seager said in a telephone interview with the Journal.
The 50-year drought was embedded in a much longer dry period that lasted about 400 years, Routson and his colleagues concluded.