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uses a slightly different set of categories in monthlynational SPI maps displayed on their website (http://www.wrcc.sage.dri.edu/spi/spi.html). Finally, Agnewsuggested the classification of categories based on the5%, 10%, and 20% occurrence probabilities, which isalso a very good system (see Agnew’s second tableon p. 10 of this issue).In his article, Agnew brings up another importantpoint that needs to be emphasized. Precipitationnormals do shift at all locations depending on theperiod being considered “normal.” Such shifts wouldcertainly have an impact when standardizing precipitationdata, but they also can affect the SPI. This iswhy it is hoped that the data sets of 100 years, or aslong as possible, could be used in determining the SPI.Guttman (1999) recommends at least 50 years of datato compute SPI values for time periods smaller than 12months, and a longer record to compute multiyear SPIvalues is desired.Finally, Agnew reminds everyone that indicesbased on precipitation alone do not take into accountspecific drought impacts. These impacts will varybased on the vulnerability of the society and environmentof each particular region. The SPI and otherindices are only tools to help decision makers understandevents that are taking place. It is good to haveone or more of these tools, but the decision makershave to become familiar with how to apply these toolsand understand their strengths and limitations in localsituations.The articles by Komuscu (1999) and Agnewdemonstrate that the number of drought monitoringapplications using precipitation indices is increasing.We welcome the discussion of indices and theirapplications in future issues of Drought NetworkNews. It is very important that this information relatingto “lessons learned” from a drought monitoring perspectiveis shared with the drought planning community.ReferencesEdwards, D. C.; and T. B. McKee. 1997. “Characteristics of20th century drought in the United States at multiple timescales.” Climatology Rep. 97–2, Department of AtmosphericScience, Colorado State University, Fort Collins,Colorado.Guttman, N. B. 1998. “Comparing the Palmer Drought Indexand the Standardized Precipitation Index.” Journal of theAmerican Water Resources Association 34(1):113–21.Guttman, N. B. 1999. “Accepting the Standardized PrecipitationIndex: A calculation algorithm.” Journal of the AmericanWater Resources Association 35(2):311–22.Hayes, M. J.; M. D. Svoboda; D. A. Wilhite; and O. V.Vanyarkho. 1999. “Monitoring the 1996 drought using theStandardized Precipitation Index.” Bulletin of the AmericanMeteorological Society 80(3):429–438.Jones, P. D.; and M. Hulme. 1996. “Calculating regionalclimatic time series for temperature and precipitation:Methods and illustrations.” International Journal of Climatology16:361–377.Komuscu, A. U. 1999. “Using the SPI to analyze spatial andtemporal patterns of drought in Turkey.” Drought NetworkNews 11(1):7–13.McKee, T. B.; N. J. Doesken; and J. Kleist. 1993. “The relationof drought frequency and duration to time scales.”Proceedings of the Eighth Conference on AppliedClimatology; pp. 179–84. American MeteorologicalSociety, Boston.McKee, T. B.; N. J. Doesken; and J. Kleist. 1995. “Droughtmonitoring with multiple time scales.” Proceedings of theNinth Conference on Applied Climatology; pp. 233–236.American Meteorological Society, Boston.Michael HayesNational Drought Mitigation Center239 L. W. Chase HallUniversity of Nebraska–LincolnLincoln, Nebraska 68583–0749USAe-mail: mhayes2@unl.edu14 Vol. 12, No. 1, Winter 1999–Spring 2000
An Introduction to the Drought MonitorOriginsThe idea of better monitoring and assessing droughthas been a quest of NDMC director Don Wilhite formore than two decades. He has been an advocate ofbetter climate monitoring, particularly drought monitoring,because drought is a normal, recurring hazardin virtually all of the United States. The challenge isto recognize drought, a slow-onset or “creeping”natural disaster, before a region is in the middle ofone.The most recent surge in interest in drought aroseduring the 1995–96 drought in the Southwest andsouthern Great Plains states. At the NDMC wediscussed how we could do a better job of trackingand assessing the severity of droughts. One questionwe often hear is “How does this drought compare, orrank, to other droughts or the drought of record forthis region or state?” Or “Just how strong or severe isthis drought?” These are complicated questions totackle. We have to take into account spatial extent,intensity, duration, and impacts on people and theaffected environment. That discussion is for anothertime.For purposes of understanding vulnerability orrisk, another question we have tried to address is“What is the degree of usualness or unusualness ofvarious droughts now and in the past?” How frequentlyor rarely do we see a drought of this magnitude,and does it occur often enough that we shouldplan for it rather than simply acknowledge it when itoccurs? In short, can we define the difference betweenperception and reality? Our hope is that theDrought Monitor and future research will begin to letus find some of the answers to these questions.Until recently, there were no comprehensive nationwideefforts to consolidate or centralize droughtmonitoring activities being conducted by or betweenvarious federal, state, or regional entities. In thesummer of 1998, I began to correspond with DougLeComte, senior meteorologist with the NationalCenters for Environmental Prediction/Climate PredictionCenter (NCEP/CPC), who shared his ideaswith us on how we might come up with a classificationsystem for droughts, much in the same way theFujita Tornado Intensity Scale (F0–F5) categorizestornadoes and the Saffir-Simpson Hurricane System(Category 1–5) rates hurricane strength. Based onLeComte’s first draft, and with the help of others, weworked on a classification scheme criteria, and as aresult the Drought Monitor was created.In spring 1999, Don Wilhite and I met withscientists at the U.S. Department of Agriculture’sJoint Agricultural Weather Facility (USDA/JAWF)and the National Oceanic and AtmosphericAdministration’s Climate Prediction Center (NOAA/CPC) to discuss working together to address the issueof tracking drought. How could we better collaborateand implement an integrated drought monitoringsystem? The signing of the National Drought PolicyAct in the summer of 1998 and the subsequentformation of the National Drought Policy Commission(NDPC) and its working groups in 1999 nodoubt helped speed up the process and fueled interestin such an effort. Monitoring and Prediction was oneof the NDPC working groups. Many of the keyplayers in the climate monitoring realm were exposedto the Drought Monitor concept and initial prototypesthrough this working group. We introduced thedrought classification system to them and welcomedthe many suggestions that followed in this informalpeer review process.As a result of the meetings in spring 1999, anagreement was reached between the NDMC, USDA,and NOAA to produce and maintain a drought monitoringproduct that would incorporate climatic dataand professional input from all levels. Requests forinput were initially sent out to National WeatherService field offices. This was followed up by contactingNOAA’s six regional climate centers (RCCs).We have invited state climatologists to comment onand review the weekly product (both map and narrative).Our intent was to create a general assessment ofdrought conditions in the United States using the mostDrought Network News15
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