US Army Corps of Engineers
US Army Corps of Engineers

National Drought Atlas


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
Miami University

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revised 1 Aug 2006



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