This past week may have brought a much-needed dose of rain to southern California, but the region still continues to suffer under devastating drought conditions. These conditions are so bad, according to researchers from the Woods Hole Oceanographic Institution and the University of Minnesota, that they now constitute California’s worst drought in 1,200 years.
The study, which was conducted by Daniel Griffin, an assistant professor in the Department of Geography, Environment and Society at the University of Minnesota, and Kevin Anchukaitis, an assistant scientist at Woods Hole Oceanographic Institution sought to determine precisely “How unusual is the 2012-2014 California Drought?”
In order to do this, they started out by looking at the trees, specifically at the rings of blue oak trees. In a press release, Griffin explained “California’s old blue oaks are as close to nature’s rain gauges as we get, they thrive in some of California’s driest environments.” And so the tree rings can show variations in moisture over centuries, and even show climate, weather and natural disaster trends.
Using the trees, Griffin and Anchukaitis were able to reconstruct rainfall data back to the 13th century. In addition, the duo also calculated the severity of the drought by “combining NOAA’s estimates of the Palmer Drought Severity Index (PDSI), an index of soil moisture variability, with the existing North American Drought Atlas, a spatial tree-ring based reconstruction of drought developed by scientists at Columbia University’s Lamont-Doherty Earth Observatory.”
What they found was surprising. Griffin said “This is California—drought happens. Time and again, the most common result in tree-ring studies is that drought episodes in the past were more extreme than those of more recent eras. This time, however, the result was different.” The 2012-2014 conditions are worse than any other consecutive years of drought conditions without reprieve.
So what does this all mean? In short, warmer temperatures are creating “hot” droughts that compounded the severity of the conditions created by an absence of rainfall. “There is no doubt,” cautions Anchukaitis, “that we are entering a new era where human-wrought changes to the climate system will become important for determining the severity of droughts and their consequences for coupled human and natural systems.”
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