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 Washington, December 15 — NOAA Scientists
reported today that droughts
more severe than the 1930s Dust Bowl could occur in the Great Plains
sometime in the next century.
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here
for
graphics.
Connie Woodhouse, a University of
Colorado research scientist working at NOAA's
National Geophysical Data
Centerin Boulder, Colo., and Jonathan Overpeck, head of NOAA's
Paleoclimatology
Program, report the results of their research in the December
issue of the Bulletin of the American Meteorological
Society.
The authors reviewed existing
paleoclimatic literature, including a variety of data sources, to
determine what droughts were like before instruments were invented,
and to compare droughts of the past 2000 years with more recent
droughts. The data sources consist of historical documents, tree
rings and archaeological remains, as well as lake, river and
wind-blown sediments.
The authors found a greater range of
drought variability in the past than found in the instrumental
record. Droughts of the 20th century have been only moderately
severe and relatively short, compared with droughts of much longer
ago. Woodhouse said that paleoclimatic records of the past 400 years
strongly indicate that the severe droughts of the 20th century, the
1930s Dust Bowl and the l950s drought, were not unusual events and
suggest that we can expect to have droughts of this magnitude once
or twice a century.
"However, when we look even farther back
in time, we see indications of droughts with much greater duration,"
said Woodhouse. During the 13th to 16th centuries, there is evidence
for two major droughts that probably significantly exceeded the
severity, length, and spatial extent of 20th century droughts, the
authors report. The most recent of these "megadroughts" occurred
throughout the western United States in the second part of the 16th
century. This drought appears to have been the most
severe and
persistent drought in the Southwest in the past 1000 to 2000 years.
Another megadrought occurred in the last quarter of the 13th
century.
"Conditions that lead to severe droughts
such as that of the late 16th century could recur in the future,
leading to a natural disaster of a dimension unprecedented in the
20th century," Overpeck said. "Besides the fact that natural
variability could have more severe droughts in store for us in the
future, two human factors could make the Great Plains even more
susceptible to a severe drought in the future. These are land use
practices and global warming."
"Even in the absence of significant
greenhouse warming, however, future droughts may be much more severe
and last much longer than what we have experienced this century,"
Woodhouse said.
Overpeck said that paleoclimatic data in
combination with instrumental data, satellite observations, and
climate models are essential to understanding the full range of
natural drought variability, and also to reduce uncertainty with
respect to what human-induced and natural climatic change will occur
in the future. | 