Drought Lands Doubled

The amount of land ravaged by droughts has more than doubled over the last 30 years, and the key factor, according to a recent analysis, appears to be the rise in global temperatures.

Scientists at the National Center for Atmospheric Research (NCAR) studied the widespread drying trends in Europe, Asia, Canada, western and southern Africa, and eastern Australia. They found that the fraction of the Earth experiencing very dry conditions rose from about 10-15 percent in the early 1970s to about 30 percent in 2002.

The researchers claim that almost half of this drastic change is due to global warming as opposed to a decrease in rainfall or snowfall. In fact, the average global precipitation has increased slightly over the past few decades.

"Global climate models predict increased drying over most land areas during their warm season, as carbon dioxide and other greenhouse gases increase," said Aiguo Dai, lead author. "Our analyses suggest that this drying may have already begun."

Warmer temperatures cause more evaporation - drying out certain areas, while drenching others in rain and snow. Evidence of the latter is the United States, which has become wetter overall -especially between the Rocky Mountains and Mississippi River - over the last 50 years, says Dai. Other parts of the world showing a moistening trend include Argentina and parts of western Australia.

"Droughts and floods are extreme climate events that are likely to change more rapidly than the average climate," Dai said. "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."

Dai will present the new findings on Jan. 12 at the American Meteorological Society's annual meeting in San Diego. The work also appears in the December issue of the Journal of Hydrometeorology.