The genesis and a short history of the development of the National
Drought Atlas are given elsewhere. A few words on the philosophy of the
Atlas, however, are in order. As initiator, editor, analyst, and writer of
portions of the Atlas, I was strongly influenced by Ray Linsley, late
Professor Emeritus of Civil Engineering at Stanford University, and a
long-time colleague. Indeed, the Atlas might well have been dedicated to
his memory. Ray strongly believed that water resources problems needed, at
a minimum, an adequate information base. If the information base did not
exist, it had to be developed. In the case of drought, a subject on which
Ray rarely, but significantly, lectured, we have had at our disposal vast
quantities of data on precipitation and streamflow that were not assembled
to make drought planning easier and more effective. I believed that by
summarizing this data in terms of frequency, national patterns could be
shown, reasonably precise information could be provided to analysts and
lay people with minimal effort on their part, and we could understand
drought across the Nation's geographic regions in some common terms.
The team of people who planned the Atlas were committed to using the
best data and the best methods currently available to compile the Atlas.
The team was also committed to employing widely recommended practices,
whether or not they were currently in widespread use; that is why, for
example, we made extensive use of the median rather than the mean as the
measure of central tendency.
I believe the Atlas will be an important step in understanding the risks
associated with extreme hydrologic events, but there are important
questions we did not pursue. We did not have the time and resources to
undertake conditional and joint probability studies. Although these are
daunting tasks, there clearly is a desire for that kind of information
among water managers. We were also unable to analyze some of the other
aspects of drought characterization that are sometimes done, such as run
length, trends, and periodicity.
Having been encouraged in the early stages of Atlas preparation by
suggestions that there was a high degree of orderliness in the data, we
looked for those properties. It would be fair to say that we looked more
carefully at similarities than at differences, although differences are
acknowledged and fairly treated as they occur. It is our hope that water
planners will find this Atlas useful, and that it will provide a stimulus
and a basis for additional analyses.
Gene E. Willeke, Ph.D., P.E.
Director, Institute of Environmental Sciences
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