Environmental Engineering Reference
In-Depth Information
challenge is accommodating the variability in the water cycle's tim-
ing and location and, more importantly, its variation from what we
see and are used to as “typical.”
Understanding Drought
Scientists and weather experts use many criteria to defi ne drought,
including the amount of moisture in the soil; how much precipita-
tion has fallen; the volume—or lack thereof—of water fl owing in
streams; the content of reservoirs, that is, how full or empty they
are; and how current conditions compare with past ones. The level
of drought severity varies based on numbers and scientifi c calcula-
tions. Basically, however, drought is a moisture defi cit over a broad
area and usually over a prolonged time. That defi cit results in short-
falls in the water needed to meet the needs of people, business, and
industry.
Climate prognosticators currently see portions of the Southwest,
Southeast, Northeast, and Hawaii experiencing varying degrees
of drought. As of the end of November 2010, about 12 percent of
the contiguous United States was characterized as in moderate to
extreme drought, according to the offi cial U.S. Drought Monitor
(http://www.ncdc.noaa.gov/sotc/drought/2010/11). The United
Nations labels much of the southwestern United States as being
in a state of “physical water scarcity.” They defi ne this as a condi-
tion where “water resources development is approaching or has
exceeded sustainable limits.” 1
Even though some places experience a month here or
a month there with plentiful rainfalls, it's the short-term Band-
Aid versus the long-term solution. Drought-plagued Huntsville,
Alabama, for example, received 10 inches of rain in December
2008. It was the fi rst time the area had that much precipita-
tion in one month since 2003, and it was enough to pull it
out of a more-than-two-year drought. In fact, December that
year provided so much rain that northern Alabama and south-
ern Tennessee had to deal with fl ooding concerns in January
2009. In April 2009, Tampa, Florida's primary reservoir was
all but dried up. The next month Florida recorded its all-time
wettest May.
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