Southwest U.S. Forests Projected by 2050 to See Worst Drought Conditions in at Least 1,000 years, With Extensive Forest Die-off

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Scientists report in the journal Nature Climate Change that the drought-stress currently being experienced by forests in the Southwestern U.S. "is more severe than any event since the late 1500s megadrought" that "probably led to deaths of a large proportion of trees living at the time." They warn that climate projections indicate that "the mean forest drought-stress by the 2050s will exceed that of the most severe droughts in the past 1,000 years."

Above: Extensive tree loss after the first afternoon and evening of the 2011 Las Conchas Fire in the Jemez Mountains, New Mexico.

In Temperature as a Potent Driver of Regional Forest Drought Stress and Tree Mortality (by A. Park Williams et al., Nature Climate Change, 30 September 2012), the authors say that the current severe drought event in the Southwest -- which extends from 2000 to the present -- is the fifth strongest since 1000 AD. They define the Southwest as including Arizona, New Mexico and the southern portions of Utah and Colorado. They attribute the current event both to natural variability and to rising atmospheric concentrations of greenhouse gases from human activity; and they associate it with "regional-scale declines in canopy greenness and tree survival, due in part to large bark-beetle outbreaks and increasingly large wildfires."

A combination of declining precipitation during the cool season and rising temperatures during the warm season is likely by mid-century to be accompanied by increased forest decline. "If forest drought stress exceeds late 1500 levels, we expect that a lot of trees are going to be dying," says the article's lead research, A. Park Williams (Los Alamos National Laboratory), in a press release today (1 October 2012) from the U.S. Geological Survey. “Consistent with many other recent studies, these findings provide compelling additional evidence of emerging global risks of amplified drought-induced tree mortality and extensive forest die-off as the planet warms,” said co-author Craig D. Allen, a research ecologist with the U.S. Geological Survey.

Above:  Drought and beetle-killed piñon pines near Flagstaff, Arizona, with some surviving trees.   Source: Craig D. Allen, USGS.

Online Resources:

Temperature as a potent driver of regional forest drought stress and tree mortality. By A. Park Williams et al. Nature Climate Change, 30 September 2012.

Climate Change to Cripple Southwestern Forests. "Trees Face Rising Drought Stress and Mortality as Climate Warms." Press release (1 October 2012) from the U.S. Geological Survey.

WWF Climate Change Blog:

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