Reply #12: Drought's Growing Reach: [View All]

Drought's Growing Reach:
NCAR Study Points to Global Warming as Key Factor

http://www.ucar.edu/news/releases/2005/drought_research.shtml


January 10, 2005

BOULDER- The percentage of Earth's land area stricken by serious drought more than doubled from the 1970s to the early 2000s, according to a new analysis by scientists at the National Center for Atmospheric Research (NCAR). Widespread drying occurred over much of Europe and Asia, Canada, western and southern Africa, and eastern Australia. Rising global temperatures appear to be a major factor, says NCAR's Aiguo Dai, lead author of the study.

Dai will present the new findings on January 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 in a paper also authored by NCAR's Kevin Trenberth and Taotao Qian. The study was supported by the National Science Foundation, NCAR's primary sponsor.

Dai and colleagues found that the fraction of global land experiencing very dry conditions (defined as -3 or less on the Palmer Drought Severity Index) rose from about 10-15% in the early 1970s to about 30% by 2002. Almost half of that change is due to rising temperatures rather than decreases in rainfall or snowfall, according to Dai.

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

Even as drought has expanded across Earth's land areas, the amount of water vapor in the air has increased over the past few decades. The average global precipitation has also risen slightly. However, as Dai notes, "surface air temperatures over global land areas have increased sharply since the 1970s." The large warming increases the tendency for moisture to evaporate from land areas. Together, the overall area experiencing either very dry or very wet conditions could occupy a greater fraction of Earth's land areas in a warmer world, Dai says.



This depiction of linear trends in the Palmer Drought Severity Index from 1948 to 2002 shows drying (reds and pinks) across much of Canada, Europe, Asia, and Africa and moistening (green) across parts of the United States, Argentina, Scandinavia, and western Australia. (Illustration courtesy Aiguo Dai and the American Meteorological Society.)