Did you know . . . - the National Drought Mitigation Center

the World Wide Web. This new product is the resultof a partnership formed in spring 1999 between theJoint Agricultural Weather Facility of the U.S. Departmentof Agriculture, the Climate Prediction Centerof the National Oceanic and Atmospheric Administration,and the National Drought Mitigation Centerat the University of Nebraska. The Drought Monitorintegrates climate information and information from avariety of indices to determine drought severity acrossthe United States. This product is updated weekly andhas been well received by technical specialists, policymakers, the media, and commercial groups. I encouragereaders to visit the Drought Monitor website(http://enso.unl.edu/monitor/) to learn more aboutthis activity and to consider how this approach mightbe modeled for other countries or regions.As some of you know, for the past two years Ihave been involved in the preparation of a book ondrought. This book, Droughts: A Global Assessment,was published in two volumes in December 1999 byRoutledge as part of a series on natural hazards anddisasters. Routledge will eventually publish sevenbooks as part of this series. Another volume, Storms,is also available, and a volume on floods should beavailable very soon. A more detailed description ofDroughts is provided on page 21 of this issue.Readers are encouraged to submit articles, announcementsof workshops and conferences, andother information of interest to our network membersto Drought Network News. The deadline for submissionfor the next issue is May 25, 2000.Donald A. WilhiteContentsCharacteristics of Drought in Kerala, India ..................................................................................... 3Using the SPI to Identify Drought ................................................................................................... 6Revisiting the SPI: Clarifying the Process ..................................................................................... 13An Introduction to the Drought Monitor ....................................................................................... 15Announcements ............................................................................................................................ 212 Vol. 12, No. 1, Winter 1999–Spring 2000

Characteristics of Drought in Kerala, IndiaKerala state in India, which is the first area of thecountry to experience the southwest monsoon, has amoist and wet climate. Kerala is in the extremesouthwestern part of the Indian subcontinent; it bordersKarnataka state in the north, Tamil Nadu in theeast, and the Arabian Sea in the west (Figure 1). Theentire state is one of the 35 meteorological subdivisionsin India.Kerala’s climate is tropical monsoon and tropicalsavanna, according to Koppen’s climatic classification(Figure 1). The state normally experiences excessiveseasonal rainfall, with hot summers (except in theextreme southern districts like Trivandrum, wheredry season and hot summer climate prevails). Thethree main seasons of the state are the hot seasonK A R NCannanoreLakshadweep SeaTropical monsoon:Seasonally excessiverainfall, hot summerTropical savannah:Seasonally dry,hot summerAKozhikodeT AAlleppeyKKERALA100 80 60 40 20 0 100MalappuramTrichurAPalghatErnakulamKottayamQuilonTrivandrumIdukkiIndian OceanFigure 1. Climatic classification of Kerala.T A MI LN A DU(March–May), southwest monsoon season (May–September), and northeast monsoon season (October–February).The annual rainfall of the state varies from 3,800mm over the north to 1,800 mm in the extreme south.The potential rainy season for Kerala is the southwestmonsoon period, which contributes more than 80%of the annual rainfall. The monsoon rain decreasesfrom the north to the south. In recent years, a trend ofdecreasing rainfall has been seen both in seasonalrainfall and 10-day extreme rainfall duration.There is significant rainfall variation in north andsouth Kerala. North and south Kerala have tworainfall distribution subzones. In north Kerala, northeastmonsoon rainfall shows a decreasing trend andcontributes about 15% of the annual rainfall. Thismay adversely affect cultivation of the second ricecrop in the area. Southwest monsoon rain, whichcontributes 82% of the area’s total rainfall, does notshow any increasing trend. Similarly, in south Kerala,southwest and northeast monsoon rains have decreasedby 5% and 8.3%, respectively. Mean annualrainfall is also decreasing in south Kerala.The decreasing rainfall over the region, late onsetof the monsoon, failure of the monsoon, and break inthe monsoon in the state lead to many drought situations.Kerala had severe dry spells and droughts in1983, 1985, 1986, and 1987, even though the statehas a wet climate. There were dry spells of 5 and 4weeks in 1985 and 1986, respectively, during thesouthwest monsoon period.Damage due to drought was particularly significantin Kerala in 1987. About 1,500 villages in 14districts were affected, and 9.82 lakh 1 hectares ofcropland and 6 lakh cattle were also affected. DuringJanuary–May 1987, the entire Kerala region wasaffected by drought. About 30% of the rabi season11 lakh = 100,000Drought Network News3

paddy crop was lost, and cash crops like coconuts,arcanuts, cashews, and bananas were damaged, resultingin a loss of Rs. 1,000 crores.Kerala also experienced a significant drought in1983. About 323,000 hectares of paddy were lost, atan estimated cost of Rs. 106.86 crores. Other majorcash crops affected were coconuts, rubber, coffee,and tea. In Ernakulam district of Kerala, 36,000hectares of paddy were lost; in Tiruchur, 33,000hectares were lost. Coconut losses of Rs. 14 croresand Rs. 11 crores were reported in Kozikode andTrivandrum districts and Kottayam district, respectively.In 1989, drought resulted in the loss of 60% ofthe cropped area in Kerala, and about 3 millionkilograms of tea, worth one crores rupees, witheredunder stress and drought.Figure 2 shows the departure of seasonal rainfallfrom normal for different years (1981–87) in theregion. Summer rains were deficient (-80%) in 1983.The southwest monsoon was about 40% of normalduring 1989 in the state. Similarly, the northeastmonsoon was highly deficient in 1986. Large rainfalldeficiencies in the various districts of the state areshown in Table 1. Figures 3a–3c reveal large waterdeficits in almost all of the representative stationsduring December to April. The seasonal dry periodand water deficits led to severe dry spells and droughts.Departure from Normal (%)40200-20-40-60Summer RainSW MonsoonNE Monsoon-801981 1982 1983 1984 1985 1986 1987Districts 1983 1984 1985 1986 1987Alleppey 21 -17 -5 -26 -17Cannanore -5 -2 1 -15 -35Ernakulam 16 9 1 19 -24Idukki -20 -3 1 1 -45Kasargode NA -3 -14 -8 -33Kottayam -28 -15 -14 -15 -28Kozikode 15 -7 -5 -14 -43Mallapuram 12 19 -7 -18 -50Palghat 17 4 2 -8 -48Pattinamathi. NA -24 -21 -35 -50Quilon 29 -18 -5 -21 -29Trichur 2 -4 -5 -25 -23Trivandrum -22 -57 -29 -44 -37Wayanad -16 9 -18 -31 -68Table 1. Percentage departure of rainfall from normal fordistricts of Kerala.The low pressure waves from the east (the Gulf ofThailand), which move across the South Bay ofBengal toward Tamil Nadu, may temporarily increaserainfall over Kerala. Also, an upper troposphericeasterly jet stream with an axis of 12°N isbelieved to influence the rainfall over the state. However,a detailed study is needed to determine this.During weak monsoons and droughts in Kerala,the orographic contribution is almost nil, but this is notattributed to a weaker westerly component during thedry spell. The Nepha (or cloud) analysis from satellitepictures over Kerala also gives good informationabout drought. During 1966, a year of weak monsoonsand drought, satellite pictures showed a zone ofcloudiness shifting far into southern India. Duringdrought situations over the state, there is no high-levelmoving system of waves in the upper troposphericeasterlies.During the drought of 1966, high-level waveflows were more or less straight easterly flows withless speed variation than in a good strong monsoonseason. Cloud analysis during active and strong monsoonssuch as occurred in 1967 shows at least 7 oktasof cloudiness on any given day over the state, extendingfrom the interior of the southern peninsula acrossFigure 2. Precipitation departure from normal for Kerala,1981–87.4 Vol. 12, No. 1, Winter 1999–Spring 2000

Water Deficit (mm)180160140120100806040Rainfall20PET0Dec. Jan. Feb. Mar. Apr.Figure 3a. Seasonal water deficit, Alleppey, Kerala.Kerala southward and westward (1,200 km from theKerala coast of the Arabian Sea). There is also asecondary maxima of 7 oktas of cloudiness south ofthe equator. This type of situation did not exist duringthe 1966 drought over the state. Thus cloud analysisand orographic rainfall patterns may give a goodindication of the drought situation in a wet state likeKerala.K. K. NathanWater Technology CentreIndian Agricultural Research InstituteNew Delhi 110 012IndiaWater Deficit (mm)25020015010050RainfallPET0Dec. Jan. Feb. Mar. Apr.Figure 3b. Seasonal water deficit, Palghat, Kerala.Water Deficit (mm)20015010050RainfallPET0Dec. Jan. Feb. Mar. Apr.Figure 3c. Seasonal water deficit, Calicut, Kerala.Drought Network News5

Using the SPI to Identify DroughtThis article was written in response to the recentanalysis of drought in Turkey by Komuscu (1999).The study showed the relationship between droughtduration, drought frequency, and drought time scaleusing the Standardized Precipitation Index (SPI):whereSPI = (X ik- X i)ó ió i= standardized deviation for the ith stationX ik= precipitation for the ith station and kth observationX i= mean precipitation for the ith stationThe index has the advantages of being easilycalculated, having modest data requirements, andbeing independent of the magnitude of mean rainfalland hence comparable over a range of climatic zones.It does, however, assume the data are normally distributed,and this can introduce complications forshorter time periods. Komuscu claims that the SPI hasnot been widely applied or tested and employs thedrought classes suggested by McKee et al. (1995),reproduced here in Table 1.The SPI is of course the same as the StandardizedRainfall Anomaly, defined by Jones and Hulme(1996) and widely used in the analysis of desiccationin drylands. Figure 1 shows a typical example of suchuse, depicting the widely reported downward trend inSahelian rainfalls (only continental Sahelian stationsare employed after the suggestions of Ba et al. [1995],Janicot et al. [1998], and Nicholson and Palao [1993]that other parts of West Africa belong to a differentclimate regime). Komuscu’s assertion that the SPI isunderused for drought assessment appears to becorrect, in that it is the persistence of the negativeanomalies that receives most attention rather than anexamination of their intensity or impact (for example,see Hulme, 1992). That is, rainfall anomalies are usedto investigate desiccation rather than drought (seeAgnew, 1995, for further discussion). The purpose ofthis paper is then to question the values assigned to theSPI for drought classes and to suggest alternative,more rational thresholds. The effect of using differentdrought classes is investigated using annual rainfallsfrom the Sahelian region of West Africa, and theSPI Probability Komuscu (1999) and Proposed newof occurrence McKee et al. (1995) drought classesdrought classesLess than -2.00 0.023 Extreme droughtLess than -1.65 0.050 Extreme droughtLess than -1.50 0.067 Severe droughtLess than -1.28 0.100 Severe droughtLess than -1.00 0.159 Moderate droughtLess than -0.84 0.201 Moderate droughtLess than -0.50 0.309 No droughtLess than 0.00 0.500 Mild drought No droughtTable 1. Probabilities for different standardized rainfall anomalies.6 Vol. 12, No. 1, Winter 1999–Spring 2000

21.5Standardized Rainfall Anomaly10.50-0.5-1-1.5-21930 1940 1950 1960 1970 1980 1990Figure 1. Standardized annual precipitation anomalies for the continental Sahel (Burkina Faso, Mali, and Niger), using the1961–90 base period.problem of changing the base averaging periods ispresented.What is Meteorological Drought?This question has been addressed time and again(Agnew and Anderson, 1992; Wilhite, 1993), and ithas often been stated that no universal definition ofdrought exists. There is little to be gained by reproducinga long list of conflicting definitions that merelyillustrate the diverse interests of those who investigatedrought. Most definitions anyway can be resolvedinto a generic statement that drought is caused by animbalance between water supply and demand. Hencedrought can be defined in terms of both supplyreduction and demand increase, and there are numerousdefinitions of hydrological, agricultural, ecological,and economic drought that demonstrate this.Many, however, agree with Palmer (1965) and Beranand Rodier (1985) that drought is essentially a meteorologicalphenomenon. The analysis below adoptsthis perspective—that examining the occurrence ofmeteorological drought is the most fundamental requirementof any investigation.The second premise of this account is that droughtis an abnormal occurrence. This is an equally importantpoint and it is the reason why it is suggested thatTable 1 should not be used without modification fordrought analysis. In McKee’s classification (McKeeet al., 1995), all negative indexes (SPI) are taken toindicate the occurrence of drought; this means for50% of the time, drought is occurring. This is clearlynonsense! It also raises the notion of “persistentDrought Network News7

drought,” which confuses drought with desiccation.Based on Warren and Khogali (1992), droughtcan be distinguished from desiccation as follows:• Drought occurs when moisture supply is abnormallybelow average for periods of up to 2 years.• Desiccation is a period of aridization broughtabout by climate change lasting decades. Thusdrought requires short-term relief, whereas desiccationrequires longer-term measures such asresettlement and land use change.When desiccation takes place, one can expect anincrease in drought frequency, but a definition ofdrought that assumes any precipitation below themean constitutes a drought will lead to exaggeratedclaims for climate change. Better that drought isdefined as an abnormal event and that a significantchange in climate is required for drought to becomepersistent.New SPI Intensity ClassesThe occurrence of drought has been widely reportedfor southern England in the 1990s, giving riseto concerns about low flows in the rivers of the region(Marsh et al., 1994; Acreman and Adams, 1998):The Environment Agency reported today that groundwaterlevels are so low in South East England that theenvironment and water supplies will be at risk nextyear if the weather remains drier than average thiswinter. (Env. Agency Press Release 04/11/1997:113/97)Approaches to the definition of low flows can bedivided into those that examine flow statistics, thosethat model hydrological processes, and those thatemploy biological/habitat conditions. Procedures forlow flow estimation in gauged and ungaugedcatchments have been produced for the United Kingdomby the Institute of Hydrology (Gustard et al.,1.41.21Cumecs0.80.60.40.2019751980 1985 1990 1995 2000Gade Bulb . Gade Q95 Bulb. Q95Figure 2. Daily flows for the Bulbourne and Gade rivers in Hertfordshire, with low flow thresholds Q95 plotted.8 Vol. 12, No. 1, Winter 1999–Spring 2000

90Percentage Occurrence80706050403020100ExtremeSevereModerateMildNo DroughtAgnewMcKeeFigure 3. Drought classes (McKee et al., 1995, and author) for annual rainfalls in the continental Sahel region between 1931and 1990, based on the 1961–90 averaging period.1992). Claussen (1995) summarized the statisticalapproaches for low flow determination in gaugedcatchments:• 7-day minimum (annual and 10-year minimum)• 1-day minimum (median annual)• 90% and 95% percentile exceedance• Base flow index (ratio of baseflow to total flow)The Q95(1) (the 95 percentile from the 1-dayflow duration curve) is commonly used and is calculatedhere for two drought-prone rivers, the Gade andthe Bulbourne, which flow in catchments some 40km north of London. The Environment Agency(1997, p. 54) described conditions in this region:The cause of low flows in rivers is attributable to acombination of factors, which include lack of rainfall. . . seasonal fluctuations in the chalk water table, andwater abstraction . . . Over the period October 1996 toSeptember 1997, rainfall and groundwater rechargein the East Chilterns [were] 88% and 51% of the longtermaverage respectively.Figure 2 shows the 1990s increase in low flows inthese rivers and the use of the Q95 threshold todemarcate abnormal deficits (curiously, annual rainfallshave been increasing in this region during the20 th century, but the winter to summer rainfall ratiohas also increased, as low rainfalls in summer are nowmore frequent). It is suggested that climatologistsshould learn from their hydrologist colleagues andemploy a threshold similar to Q95 for defining meteorologicaldrought.The SPI drought thresholds recommended heretherefore correspond to 5%, 10%, and 20% probabilities.Hence drought is only expected 2 years in 10 andextreme drought only 1 year in 20. This, it is believed,is a more realistic drought frequency than that used byKomuscu, and it corresponds to the employment ofthe term abnormal occurrence, as used in otherbranches of environmental science.The impacts of changing the drought class boundariesare exemplified in Figure 3, based on the dataused to draw Figure 1. It is evident that little changeis made for extreme drought conditions, but the mostimportant effect is to reduce the incidence of mildmeteorological droughts. It may seem curious thatthere are a large number of no-drought years (68% or86% for McKee et al. [1995] or the author’s classes,respectively) given the widespread reports of droughtDrought Network News9

Drought McKee et al. 1961–90 1931–60 Agnew 1961–90 1931–60class (1995) base period base period base period base periodSPI value McKee McKee SPI value Agnew AgnewExtreme

765Standardized Rainfall Anomaly43210-1-2-3-4-5-6-71930 1940 1950 1960 1970 1980 1990Mean Max MinFigure 4. Average standardized precipitation anomalies for the continental Sahel using the 1961–90 base averaging periodand the maximum and minimum anomalies observed at individual stations.through time. Hence purely statistical definitions ofmeteorological drought should be treated with caution.Perhaps of equal significance is the omissionwithin the SPI of any assessment of persistence. It israre that drought in any one year causes major hardship.It is the sequence of low rainfalls that createsdifficulties. For example, in England the drought of1976 was really caused by the low rainfalls in thepreceding year, while the drought of 1992 was theresult of the low rainfalls from 1988. The SPI thereforeneeds to be developed from merely classifyingintensities to include drought sequences, and theselection of appropriate averaging periods needs moreattention.AcknowledgmentsThe annual rainfall totals were generously providedby the Climate Research Unit at the University of EastAnglia. The river flow data was provided by theEnvironment Agency, United Kingdom.C. T. AgnewDepartment of GeographyUniversity College London26 Bedford WayLondonWC1H OAPUnited KingdomReferencesAcremen, M.; and B. Adams. 1998. Low Flows, Groundwaterand Wetland Interactions. Vol. 1, Issues Report to theDrought Network News11

Environment Agency, UKWR and NERC. Institute of Hydrology,Wallingford, UK.Agnew, C. T. 1995. “Desertification, drought and developmentin the Sahel.” In A. Binns, ed. People and Environmentin Africa; pp. 137–149. J. Wiley & Sons, Chichester, UK.Agnew, C. T.; and E. Anderson. 1992. Water Resources in theArid Realm. Routledge, London.Agnew, C. T.; and A. Chappell. 1999. “Drought in the Sahel.”Submitted to GeoJournal.Ba, M. B.; R. Frouin; and S. E. Nicholson. 1995. “Satellitederived interannual variability of West African rainfallduring 1983–88.” Journal of Applied Meteorology 34:411–431.Beran, M. A.; and J. A. Rodier. 1985. Hydrological Aspects ofDrought. Studies and Reports in Hydrology 39. UNESCO-WMO, Geneva.Claussen, B. 1995. “Discharge data collection and analysisstrategies in low flow studies.” Nordic Hydrology 26:191–204.D’Amato, N.; and T. Lebel. 1998. “On the characteristics of therainfall events in the Sahel with a view to the analysis ofclimatic variability.” International Journal of Climatology18:955–974.Downing, T. 1992. Climate Change and Vulnerable Places.Research Report No. 1. Environmental Change Unit, OxfordUniversity, Oxford, UK.Environment Agency. 1997. Local Environment Agency Plan,Colne consultation report. E. A. Thames region, Reading,UK.Gustard, A.; A. Bullock; and J. M. Dixon. 1992. Low FlowEstimation in the U.K. IH Report 108. Institute of Hydrology,Wallingford, UK.Hulme, M. 1992. “Rainfall changes in Africa.” InternationalJournal of Climatology 12:685–699.Janicot, S.; A. Harzallah; B. Fontaine; and V. Moron. 1998.“West African monsoon dynamics and eastern equatorialAtlantic and Pacific SST anomalies (1970–88).” Journal ofClimate 11:1,874–1,882.Jones, P. D.; and M. Hulme. 1996. “Calculating regionalclimatic time series for temperature and precipitation: Methodsand 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.Marsh, T. J.; R. A. Monkhouse; N. W. Arnell; M. L. Lees; andN. S. Reynard. 1994. The 1988–92 Drought. HydrologicalData UK Series. Institute of Hydrology, Wallingford, UK.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.Nicholson, S. E.; and I. M. Palao. 1993. “A re-evaluation ofrainfall variability in the Sahel.” International Journal ofClimatology 13:371–389.Palmer, W. C. 1965. Meteorological Drought. Research Paper45. U.S. Weather Bureau, Washington, D.C.Warren, A.; and M. Khogali. 1992. Assessment of Desertificationand Drought in the Sudan–Sahelian Region 1985–1991. UNSO, New York.Wilhite, D. A. 1993. “The enigma of drought.” In D. A. Wilhite,ed. Drought Assessment, Management, and Planning: Theoryand Case Studies; pp. 3–15. Kluwer Academic Publishers,Boston, Dordrecht, and London.12 Vol. 12, No. 1, Winter 1999–Spring 2000

Revisiting the SPI: Clarifying the ProcessThe number of applications using the StandardizedPrecipitation Index (SPI) around the world continuesto increase (e.g., Agnew, pp. 6–12 of thisnewsletter, and Komuscu 1999). However, there arerelatively few publications explaining the SPI, andoccasional misconceptions about the index have occurred.When the SPI was first developed by McKee etal. (1993, 1995), it was meant to address some of thelimitations that exist within the Palmer Drought Index(PDI). These first publications were relatively simpleintroductions of the SPI to the scientific community,appearing in the Proceedings of the Eighth and NinthApplied Climatology Conferences, respectively,sponsored by the American Meteorological Society.In both cases, the authors define the SPI as the“difference of precipitation from the mean...dividedby the standard deviation.” It is this equation, givenby Komuscu (1999) and repeated by Agnew, thatcauses confusion about the SPI.Agnew is correct to point out that the “differenceof precipitation from the mean divided by the standarddeviation” standardizes the data and has beencalled the “Standardized Rainfall Anomaly” by Jonesand Hulme (1996). Variations of standardized rainfallanomalies have been used with data sets, especiallyanalyzing African rainfall. It is important topoint out, however, that this is not the SPI! There is adifference between standardizing precipitation datausing the equation above and the SPI, and it is easy tomiss this difference. In the cases of McKee et al.(1993, 1995) and Komuscu (1999), the authors brieflymention that the long-term data sets used to determinethe SPI at any time scale must first be normalized.Readers of these articles may overlook this step. Thenormalization procedure using a probability distributionis a very important feature of the SPI and makesit unique. Edwards and McKee (1997) first highlightthis important distinction and give a detailed descriptionof how this is done for the SPI. People willfrequently ask, “What is the equation of the SPI?”Edwards and McKee (1997) illustrate that it is moreof a “process” to determine an SPI value.In 1998, Guttman wrote an article comparing theSPI with the PDI that contained a more detailedexplanation about determining the SPI. Hayes et al.(1999) also contains a detailed description of theprocess. Guttman (1999) went into the specificsabout different probability distributions applied to thelong-term data sets and examined the impact of sixdistributions on the SPI. The recommendation fromGuttman (1999) is that the Pearson Type III distributionis “best” suited to normalize the long-term datasets when calculating the SPI. Edwards and McKee(1997) used the two-parameter gamma distribution tocalculate the SPI. Guttman (1999) also recommendedthat the procedure be uniform for everyone so thatapplications of the SPI would be consistent. Differentsoftware versions to determine the SPI are nowavailable from Colorado State University and theNational Climatic Data Center.Agnew makes another very good point aboutidentifying appropriate drought categories, and pointsout that the initial categories identified in the originalMcKee et al. (1993, 1995) articles had a location forany time period in some stage of “drought” 50% of thetime. Table 1 below shows the NDMC modificationsto the categories identified by Agnew in his table onp. 6 of this issue. The term dry is used because that ismore appropriate for short time scales, and the categoriesreflect the lower percentages that should occurwith dry periods, especially with the labels severe andextreme. These categories are also the basis for themonthly national SPI maps that are displayed on theNational Drought Mitigation Center’s website (http://enso.unl.edu/watch/). Guttman (1999) uses the samecategories. The Western Regional Climate Center2.0 + extremely wet1.5 to 1.99 very wet1.0 to 1.49 moderately wet-.99 to .99 near normal-1.0 to -1.49 moderately dry-1.5 to -1.99 severely dry-2 and less extremely dryTable 1. SPI values.Drought Network News13

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

elevant and current data that each entity involved hadto offer. The selected data were then put into anexperimental product using a new drought classificationsystem approach. The first experimental droughtmap was put out for internal review and comment inMay 1999. An e-mail exploder group was set up andis maintained at the NDMC. This allows all reviewersand authors of the product to discuss and share theirrelevant expertise, viewpoints, and concerns.The experimental tag was short-lived. TheDrought Monitor quickly evolved into a more permanentproduct as a result of the efficient partnershipsbetween USDA, NOAA, NDMC, RCCs, and a fewstate climatologists. No doubt the drought in theNortheast in summer 1999 provided an extra incentivefor the map. The Drought Monitor was officiallylaunched at a joint White House press conferencebetween the Department of Commerce (NOAA) andUSDA in August 1999. The Drought Monitor hadgone from an experimental bi-weekly map to a fullfledgedoperational product in a few months. With thesupport of USDA’s chief meteorologist, the NationalDrought Mitigation Center at the University of Nebraska–Lincolnagreed to set up and maintain thehome page for the Drought Monitor (http://enso.unl.edu/monitor/monitor.html).Since its unveiling, the Drought Monitor has beenwell received by people from a wide variety ofbackgrounds and trades. The media has been especiallyquick to pick up on and use the new product toinform their readers and listeners. Producers, commoditybrokers, congressional delegations, and federal/stateagencies also are using this product. Theyseem to like the simplicity and ease of use of theproduct (see Figure 1), rather than having to learnabout another new index.The ConceptThe Drought Monitor consists of a color map,showing which parts of the United States are sufferingfrom various degrees of drought, and accompanyingtext. The text describes the drought’s currentimpacts, future threats, and prospects for improvement.The Drought Monitor is a synthesis of severaldifferent scientific drought indices. It is by far themost user-friendly national drought monitoring product,and it is particularly well suited for use bymainstream media because it represents state-of-theartscientific expertise and is packaged as a timely,colorful, unambiguous map. Currently, the WorldWide Web is the main means of distributing theDrought Monitor. NOAA also distributes the mapthrough their internal channels. The obvious advantagesto using the web are that there are no distributioncosts and the information is instantly available andalways current. The obvious disadvantage is that noteveryone has access to the web. Our focus to thispoint has been how to best disseminate the product inthe most timely manner.No single definition of drought works in allcircumstances, so water planners rely on indices ordata in various forms, and most often depicted in mapor graphic form, to recognize droughts. The authorsof the Drought Monitor also rely on the input ofseveral key indices and ancillary indicators fromdifferent agencies to create the final map, which isposted each Thursday. The seven key parametersmaking up the current scheme are the Palmer DroughtIndex, Crop Moisture Index, CPC Soil MoistureModel (percentiles), USGS Daily Streamflow (percentiles),Percent of Normal Precipitation, USDA/NASS Topsoil Moisture (percent short and veryshort), and a remotely sensed Satellite VegetationHealth Index. The final color map summarizes all ofthis information in an easy-to-read format that showswhere drought is emerging, lingering, and subsiding.Classification: D0–D4The idea is to classify droughts on a scale fromzero to four (D0–D4), with zero indicating an abnormallydry area and four reflecting a region experiencingan exceptional drought event (likened to a droughtof record). The drought intensity categories are basedon six key indicators and many supplementary indicators.The Drought Monitor summary map andnarrative identify general drought areas, labelingdroughts by intensity from least to most intense. D0areas (abnormally dry) are either drying out and16 Vol. 12, No. 1, Winter 1999–Spring 2000

February 8, 2000 Valid 7 a.m. ESTU.S. Drought MonitorD1(A)Map focuses on widespread drought.Local conditions may vary.D rought type: used onlyw hen impacts differDEPARTMENT OF COMMERCEUNITED STATES OF AMERICAA = AgricultureW = WaterF = W ildfire dangerP lus (+) = Forecast to intensify next two weeksM inus (-) = Forecast to diminish next two weeksN o sig n = No chang e in drought classification forecastReleased Thursday, Feb. 10, 2000Figure 1. The Drought Monitor (http://enso.unl.edu/monitor/monitor.html).Drought Network News17

possibly heading into drought or recovering fromdrought but still experiencing lingering impacts (ornot yet back to normal or wet conditions).Categories: A, W, and FThe Drought Monitor also shows which sectorsare presently seeing the majority of impacts due todrought, using labels of A, W, or F. An A representsimpacts on agriculture (crops, livestock, range orpasture). Water (W), or hydrological, impacts showthat the region is experiencing an impact on some partof the water supply system. In determining whether touse this label, we look at how droughts affectstreamflow, snowpack, groundwater, and reservoirs.An F is used when abnormally high risks of firedanger are observed.ForecastsWe use the two week forecasts (5 day and 6–10day) to determine if the drought is intensifying ordying out. Intensifying drought is indicated by a plus(+) sign after the drought classification; decreasingdrought is indicated by a minus (-) sign after thedrought classification.drought. Efforts are underway to better forecast, withhigher confidence, further into the future.Currently, seasonal forecasts issued by the CPCare taken into account, but they are not used indetermining intensity trends. We do know that somestrong relationships exist between dryness or droughtin certain parts of the United States, depending on theseason and whether or not we are in an El Niño or LaNiña phase. The relationship isn’t nearly as strong,however, in the continental grain-producing regionsthat make up our corn and wheat belts. The problemis addressing the non-phase year, especially in thesummer. In fact, the summer months are the toughestto predict, regardless of whether an ENSO event istaking place. Today’s models are much better thanever before, and they will continue to improve ascomputing power increases and we better identifyand understand the complex relationships that existbetween our oceans, continents, and atmosphere.Classification ParametersTable 1 illustrates the drought severity classificationsystem that exists now. The system was intendedto be flexible, allowing it to continually evolve byresponding to and incorporating the latest technologiesand data available in the monitoring world.An ExampleAn area shaded and labeled as D2 + (A) is ingeneral experiencing severe drought conditions thatare affecting the agricultural sector but at present arenot affecting water supplies. The area is not seeing aheightened fire risk in association with this dryness.In addition, the drought looks like it will intensify inthe next two weeks, according to the forecasts.Droughts are generally slow in developing andcan be slow in receding, but there are cases (like thehurricanes in the Northeast this past summer) inwhich a drought-breaking type of event can speed upthe recovery process. Even after the physical event isover, impacts may linger for months or years, dependingon the timing, duration, and intensity of theThe FutureThe CPC has been experimenting with blendingup to three inputs to produce a weighted objectivedrought index, but this is continually going throughadjustments and is only one part of the equation welook at when making the Drought Monitor. Weexpect to see CPC and others improve the accuracyand confidence of forecasts at all time scales. Thisprocess and product are still evolving as both monitoringand forecasts improve. For example, we alsohope to integrate USDA and other soil moisturenetwork data into the Drought Monitor in the nearfuture. Interestingly, it is the availability and input ofthese parameters (i.e., soil moisture) that in turn serveas inputs into better models at better resolutions. We18 Vol. 12, No. 1, Winter 1999–Spring 2000

Drought Network NewsTable 1. Drought severity classification.Category Description Impacts Palmer CPC Soil Daily Percent of USDA/ SatelliteDrought Moisture Streamflow Normal NASS VegetationIndex or Model (Percentiles) Precipitation Topsoil HealthCrop (Percentiles) Moisture IndexMoisture(% short &Indexvery short)D0 Abnormally Short-term dryness slowing -.6 – -1.9 21–30 21–30

would like to include seasonal (long-lead) forecasts inthe Drought Monitor to give people as much informationas possible (and as soon as possible) to use indecision making.Although the maps are based on many inputs, thefinal maps are tweaked to reflect real-world conditionsas reported by numerous experts throughout thecountry. States or water suppliers may be looking atour indicators while also using many other local dataresources and tailored drought triggers. Our intent isnot to replace any local or state information or subsequentlydeclared drought emergencies or warnings.Instead, we are providing a general assessment of thecurrent state of drought around the United States,Pacific possessions, and Puerto Rico.We hope we have found a way to better picturethis “freeze-frame” disaster and relay the informationto users. Ultimately, it is the users who determine howto use the information; it is our job to provide themwith the best available data and product in a timelyfashion.Mark SvobodaNational Drought Mitigation Center107 L. W. Chase HallUniversity of Nebraska–LincolnLincoln, Nebraska 68583–0749USAe-mail: msvoboda2@unl.edu20 Vol. 12, No. 1, Winter 1999–Spring 2000

AnnouncementsNew BooksDroughts: A Global AssessmentDroughts: A Global Assessment has been published in two volumes by Routledge as part of aseries of definitive works on major hazards and disasters. The series is being published to mark the endof the International Decade for Natural Disaster Reduction.Donald Wilhite of the National Drought Mitigation Center is the editor of Droughts. More than75 leading international researchers in the field contributed to the volume. Through an extensive rangeof case studies covering the most drought-prone and most drought-affected countries, the contributorsexamine new technology, planning methodologies, and mitigation actions from recent droughtexperiences worldwide.Following a discussion of the critical concepts of drought, the book is divided into seven additionalparts that address causes and predictability; monitoring and early warning techniques; impacts andassessment methodologies; adjustment and adaptation strategies; policy, mitigation techniques, andpreparedness methodologies; links between drought and other global issues; and conclusions andfuture challenges. With its emphasis on both the physical and social dimensions of drought andproposed management actions and policies, this volume will be helpful to those seeking a greaterunderstanding of this complex natural hazard.The cost of the two-volume set is US$275/UK£225. The ISBN (International Standard BookNumber) of Droughts is 0–415–16833–3. In North America, copies may be ordered from Routledgeat 1 (800) 634–7064. Routledge’s United Kingdom customer hotline is 01264 342939 (+44 1264342939), or fax: 01264 343005 (+44 1264 343005). Their website is www.routledge.com.Proceedings of the National Workshop on Dynamic Crop Simulation Modeling forAgrometeorological Advisory ServicesThe Proceedings of the National Workshop on Dynamic Crop Simulation Modeling forAgrometeorological Advisory Services has been published. The workshop was conducted at theNational Centre for Medium Range Weather Forecasting (NCMRWF), Department of Science andTechnology, New Delhi, in January 1999. The volume includes papers presented at the workshop onvarious themes of crop modeling and the recommendations that evolved from the deliberations of theworkshop. S. V. Singh, L. S. Rathore, S. A. Saseendran, and K. K. Singh are the editors; the volumeis published by the NCMRWF. For further information and copies of the publication, please contactDr. S. A. Saseendran, Scientist, NCMRWF, DST, Mausam Bhavan, Lodi Road, New Delhi–3, India;e-mail: saseendransa@hotmail.com.Drought Network News21

ConferencesCentral and Eastern European Workshop on Drought MitigationThe Central and Eastern European Workshop on Drought Mitigation will be held April 12–15, 2000, inBudapest, Hungary. The workshop is being presented by the Ministry of Agriculture and Rural Development;Ministry of Environmental Protection; and Ministry of Transport, Communication and Water Management ofthe Hungarian Republic.The workshop will provide a forum for discussing various aspects of drought monitoring, strategies, impactassessment, and mitigation, with special regard to the central and eastern European (CEE) region. Topics willinclude the status of national drought mitigation strategies in the CEE countries and impacts of drought ondifferent areas of the economy. For more information, contact the Budapest Station for Plant Health and SoilConservation, Department of Informatics, Budaörsi út 141–145, H–1118 Budapest, Hungary; telephone: (36–1) 309–1000; fax: +36–1–246–2942.11th Global Warming International Conference and ExpoThe 11th Global Warming International Conference and Expo will be held April 25–28, 2000, in Boston,Massachusetts. The objective of the conference is to provide a comprehensive international and interdisciplinaryreview forum for resource and technology managers on global warming, its impacts on all economicsectors, its effective mitigation, and each nation’s compliance with the Kyoto Protocol to reduce greenhousegas emissions. Topics include Global Warming and Climate Change; Global Surveillance: Climate Future;Education: Global Change; Human Health in a Changing Climate; Energy and Natural Resource Management;International Law and Policy Making; and State and Local Government Actions. For more information,contact the Global Warming International Center, P.O. Box 5275, Woodridge, Illinois 60517–0275, USA; fax:+1 630–910–1561; website: http://GlobalWarming.net.New ProductsGLOBE Data SetThe NOAA National Geophysical Data Center (NGDC) has released the Global Land One-kilometerBase Elevation (GLOBE) digital elevation data set. GLOBE is an international effort to create a global digitalelevation model on a nominal 1-kilometer grid. Source data for GLOBE include satellite imagery, aerialphotography, satellite altimetry, cadastral survey data, and hardcopy topographic maps converted to digitalformat. There are two versions of GLOBE: an unrestricted version with full global coverage and no copyrightor security restrictions on its distribution, and a version with high-quality data that honors copyright. GLOBEdata can be obtained via the web and as a CD collection. GLOBE data, documentation, and visualizations areavailable at no charge at http://www.ngdc.noaa.gov/seg/topo/globe.shtml. The CD-ROM collection (fourCDs), with documentation, is available from NOAA/NNDC/National Geophysical Data Center. For moreinformation, contact the National Environmental Satellite, Data, and Information Service, NOAA NationalData Centers, National Geophysical Data Center, 325 Broadway, Boulder, Colorado 80303, USA; telephone:(303) 497–6277; e-mail: seginfo@ngdc.noaa.gov; website: http://www. ngdc.noaa.gov/store/.22 Vol. 12, No. 1, Winter 1999–Spring 2000

Material from this newsletter may be reproduced with acknowledgment of the source.Drought Network News is published three times a year by the International Drought Information Center (IDIC) and National Drought Mitigation Center(NDMC). The IDIC and NDMC are part of the School of Natural Resource Sciences at the University of Nebraska–Lincoln. Funding for the newsletter is providedby the International Activities Division, National Weather Service/NOAA, through their cooperative program with the World Meteorological Organization, andCooperative State Research, Extension, and Education Service, U.S. Department of Agriculture.Drought Network News encourages readers to submit information on current episodes of drought and its impacts; timely reports of response, mitigation,and planning actions of governments and international organizations (successes and failures); recent research results and new technologies that may advancethe science of drought planning and management; recent publications; conference reports and news of forthcoming meetings; and editorials. If referencesaccompany articles, please provide full bibliographic citations. All artwork must be camera-ready—please provide clear, sharp copies (in black/gray and whiteonly—we are unable to reproduce color artwork) that can be photocopied/reduced without losing any detail. Correspondence should be addressed toDrought Network News Telephone: (402) 472–6707IDIC/NDMC fax: (402) 472–6614239 L. W. Chase Hall e-mail: ndmc@enso.unl.eduUniversity of Nebraskawww: http://enso.unl.edu/ndmcP.O. Box 830749Lincoln, NE 68583–0749USASubscriptions to Drought Network News may beobtained, free of charge, by contacting Kim Klemsz atthe street or e-mail address or the telephone or faxnumber to the left.Director: Donald WilhiteClimate Impacts Specialist: Michael HayesClimate/Water Resources Specialist: Mark SvobodaWater Resources Specialist: Cody KnutsonInformation Specialist: Kelly Helm SmithPublications Specialist: Deborah WoodSecretary: Kim KlemszSystems Analyst: James HinesInstitute of Agriculture and Natural Resources, University of Nebraska-LincolnDrought Network News23