Agriculture Reference
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Fig
ure 9.1
Dryland corn yield for Nebraska, 1950-2002 (from U.S. Department of Agricul-
ture, National Agricultural Statistics Service, Washington, DC;
www.nass.usda.gov).
[122
Line
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0.0
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Long
PgEn
D
rought Monitoring Program
After the creation of the National Drought Mitigation Center (NDMC) in
1995, one of our first goals was to create a “one-stop shopping” section on
our Web site that would provide users with access to all the information for
drought monitoring in a timely and reliable fashion. The development of
the “drought watch” section was undertaken because no routine national
or regional integrated assessment was available from federal agencies. This
section has evolved into the “Monitoring Drought” section of the NDMC
Web site (drought.unl.edu). Currently, drought monitoring in the United
States relies heavily on a product called the U.S. Drought Monitor, which
draws on the climate and water supply indicators and indices such as
Palmer drought severity index (PDSI) and the standardized precipitation
index (SPI).
[122
Pa
lmer Drought Severity Index
The PDSI was developed by W.C. Palmer (1965) for monitoring droughts
in terms of their intensity, duration, and spatial extent. Although there are
several variations of the index, each variation has characteristics similar to
the PDSI (Palmer, 1965; Karl and Knight, 1985; Heddinghaus and Sabol,
1991). Palmer based the PDSI on anomalies in the supply and demand
concept of the water balance equation. Inputs into weekly or monthly
calculations include precipitation, temperature, and the local antecedent
soil moisture conditions. The data are standardized to account for regional
differences so that the PDSI values can be compared from one location to
another. Therefore, identical PDSI values, in theory, in the Midwest and
Texas indicate the same severity of drought, even though actual rainfall
deficiencies would be different at the two locations.
Weekly maps of a modified PDSI (Heddinghaus and Sabol, 1991) are
produced by the Climate Prediction Center (CPC) of the National Oceanic
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