The portion of our planet affected by serious drought has doubled in the last three decades, a new study suggests. Findings to be presented today at the annual meeting of the American Meteorological Society in San Diego, Calif., indicate that the fraction of global land characterized as "very dry" has increased from 10 to 15 percent in the 1970s to nearly 30 percent in 2002.
Dry conditions in the U.S. are classified according to the Palmer Drought Severity Index, which compares the amount of moisture in the soil to that in the air closest to the surface. Using long-term temperature and precipitation records from 1870 to 2002, Aiguo Dai of the National Center for Atmospheric Research and colleagues calculated the Palmer index for locations around the world in which it is not routinely used. "Droughts and floods are extreme climate events that are likely to change more rapidly than the average climate," says Dai. "Because they are among the world's costliest natural disasters and affect a very large number of people each year, it is important to monitor them and perhaps predict their variability."
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