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Extramural Research

Tree Rings Used to Identify Past Droughts in the US Southwest

This cross-section of Douglas-fir from Arizona shows the tree's annual growth rings. Each ring has a light-colored band, or earlywood, that forms in the spring and a dark-colored band, or latewood, that forms in the summer. The width of the band tells how much the tree grew during that period and therefore can be used as a proxy for the climate during that season. (Image (c) Daniel Griffin/University of Arizona) Daniel Griffin, a 2010 Fellowship recipient has been researching the use of tree-ring analysis to reconstruct ­­­­monsoon records over the past 500 years in America’s southwest. Griffin has found that the monsoon droughts of the past were more severe and persistent than any of the last 100 years. He found that in earlier centuries, the droughts involved both the winter and summer seasons, unlike the recent rain records from 1950-2000 which show dry seasons alternated with wet ones. The earlier droughts had major environmental and social effects which caused landscape scale vegetation changes. Although winter rainfall is important to replenishing water supplies, these data show the importance of more recent summer monsoon seasons in having a mediating effect on water demand.

Griffin and his research team have recently published results in Geophysical Research Letters from the American Geophysical Union. The next steps in their research are to possibly expand the research area, into Mexico and more of the Southwest, and/or look at the history of Southwest wildfires.

To find out more about the Fellowship Program visit: Fellowships

For more information on the AGU press release visit: Loss of Summer Rains Stoked Long Droughts in Southwest Exit EPA Click for Disclaimer
Geophysical Research Letters link: North American monsoon precipitation reconstructed from tree-ring latewood Exit EPA Click for Disclaimer
For the University Arizona News Release visit: Monsoon Failure Key to Long Droughts in Southwest Exit EPA Click for Disclaimer

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