Pinyon pine forests near Los Alamos, N.M., had already begun to turn brown from drought stress in the image at left, in 2002, and another photo taken in 2004 from the same vantage point, at right, show them largely grey and dead. (Photo by Craig Allen, U.S. Geological Survey)
The chronic drought that hit western North America from 2000 to 2004 left dying forests and depleted river basins in its wake and was the strongest in 800 years, scientists have concluded, but they say those conditions will become the “new normal” for most of the coming century. Such climatic extremes have increased as a result of global warming, a group of 10 researchers reported today in Nature Geoscience. And as bad as conditions were during the 2000-04 drought, they may eventually be seen as the good old days.
Climate models and precipitation projections indicate this period will actually be closer to the “wet end” of a drier hydroclimate during the last half of the 21st century, scientists said. Aside from its impact on forests, crops, rivers and water tables, the drought also cut carbon sequestration by an average of 51 percent in a massive region of the western United States, Canada and Mexico, although some areas were hit much harder than others. As vegetation withered, this released more carbon dioxide into the atmosphere, with the effect of amplifying global warming.
“Climatic extremes such as this will cause more large-scale droughts and forest mortality, and the ability of vegetation to sequester carbon is going to decline,” said Beverly Law, a co-author of the study, professor of global change biology and terrestrial systems science at Oregon State University, and former science director of AmeriFlux, an ecosystem observation network. ”During this drought, carbon sequestration from this region was reduced by half,” Law said. “That’s a huge drop. And if global carbon emissions don’t come down, the future will be even worse.”