Drought monitoring and early warning: concepts, progress and future challenges

7/31/2019 Drought monitoring and early warning: concepts, progress and future challenges

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Dru iri d

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WMO - No. 1006

Weather and climate information for

sustainable agricultural development


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WMO-No. 1006

2006, World Meteorological OrganizationISBN 92-63-11006-9

Cover illustration: Maasai tribesman walking through drought-stricken landscape, Kenya. Jonathan and Angela (Getty Images)

NOTE

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever

on the part of the Secretariat of the World Meteorological Organization concerning the legal status of any country, territory, city or

area, or of its authorities, or concerning the delimitations of its frontiers or boundaries.


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Contents

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Australia . ..23

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FoReWoRD

Throughoutthecourseohumanhistory,drought

hasbeenaproblemaectingourwelareandood

security.Oallhumanendeavours,agriculturewas

perhaps the rst sector or which humans recog-

nized the strongrelationships between cropsand

weather.Short-termrainalldecitspromptedearly

humans to nd alternative ood crops. However,

evenasingleyearwithaseveredroughtduringthe

rainyseasonresultedincropailures,whichmost

likelyledtohumansmigratingtootherareas.There-

ore,inearlyhumanhistory,evenlimiteddroughtshadlargeimpacts.

In recent times, short-term drought adaptation

mechanismshaveimproved,butextendedperiods

o drought are now the main concern or human

welareandoodsecurity.Theseperiodsodryness,

whencoupledwithotherclimaticactors,suchas

extremerainallandwindeventsorunsustainable

agricultural and development patterns, can result

inlanddegradationand,iunchecked,inincreases

in desert land areas or desertication. During the

1970s and 1980s, West Arica experienced anextendedperiododroughtthatledtowidespread

concernabouttheseissuesTheaggregateimpact

odroughtcanbequitenegativeontheeconomies

odevelopingcountries,inparticular.Forexample,

GDPellby8to9percentinZimbabweandZambia

in1992and4to6percentinNigeriaandNigerin

1984.Over250millionpeoplearedirectlyaected

bylanddegradationanddesertication.Inaddition,

someonebillionpeopleinover100countriesareat

risk.Theyincludemanyotheworldspoorestand

mostmarginalizedcitizens.Hence,combatingdeser-

ticationisanurgentpriorityintheglobaleor tsto

ensureoodsecurityandthelivelihoodsomillionsopeoplewhoinhabitthedrylands.

Asvulnerabilitytodroughthasincreasedglobally,

greaterattentionhasbeendirectedtoreducingthe

risks associated with its occurrence through the

introduction o planning to enhance operational

capabilities such as climate and water supply

monitoringandbuildinginstitutionalcapacity,and

mitigationmeasuresthatareaimedatreducingthe

impactsodrought.

Importantcomponentsoeectivedroughtmanage-ment are improved drought monitoring and early

warning systems. The ght against drought and

desertication receives a high priority in WMOs

Strategic Plan, particularly under the Agricultural

Meteorology Programme, the Hydrology and

Water Resources Programme and the TechnicalCooperation Programme. WMO actively involves

the National Meteorological and Hydrological

Services (NMHSs), the regional and sub-regional

meteorological centres and other bodies in the

improvement o hydrological and meteorological

networksorsystematicobservationsandexchange

and analysiso data.WMO also works closely with

other UN agencies and international organizations

to develop long-term strategies aimed at promot-

ing meteorological and hydrological activities that

contributetobetterdroughtmonitoringanduseo

medium- and long-range weather orecasts and to

assistinthetranseroknowledgeandtechnology.

Atits58thordinarysession,theUnitedNationsGeneral

Assemblydeclared2006tobetheInternationalYear

o Deserts and Desertication (IYDD). In doing so,

the General Assembly underlined its deep concern

or the exacerbation o desertication, particularly

in Arica, and noted its ar-reaching implications or

the implementation o the Millennium Development

Goals(MDGs),whicharetobemetbytheyear2015.

TheIYDDpresentsagoldenopportunitytoconveythe

message strongly and eectively in the sense that

issues o drought, land degradation and desertica-tion are global problems that must be addressed. It

also provides animpulseto strengthen the visibility

andimportanceothedrylandsissueontheinterna-

tionalenvironmentalagenda,whileprovidingatimely

M. Jarraud, Secretary-General


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remindertotheinternationalcommunityothehuge

challengesthatstilllieahead.

TheUnited NationsConvention toCombat Deserti-

cation (UNCCD) and WMO have been longstanding

partners in developing and promoting the issues

related to drought monitoring, preparedness, miti-

gation, land degradation and desertication. As

partoitsimplementationactivitiesorIYDD,WMO

has prepared this brochure to explain the various

conceptsandchallengesodroughtmonitoringandearly warning systems. This brochure also details

the considerable progress that has been made on

theseissuesinsomedrought-pronecountriesbyhigh-

lightingseveralcasestudiesromaroundtheworld.

IwishtothankMrDonaldWilhite,DirectorotheNational

DroughtMitigationCenterandProessorotheSchool

o Natural Resources o the University o Nebraska

(USA),orpreparingthisinormativebrochure.Wehope

thatthisdocumentwillbeuseultocountrieslookingto

developorenhancetheirowndroughtmonitoringand

earlywarningcapabilities.


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IntRoDUCtIon

Droughtisaninsidiousnaturalhazardcharacterized

bylowerthanexpectedorlowerthannormalprecip-

itationthat,whenextendedoveraseasonorlonger

periodotime, isinsucient tomeetthedemands

o human activities and the environment. Drought

isatemporaryaberration,unlikearidity,whichisa

permanenteatureoclimate.Seasonalaridity,that

is,awell-deneddry season,alsoneedstobe dis-

tinguished rom drought, as these terms areoten

conusedorusedinterchangeably.Thedierences

needtobeunderstoodandproperlyincorporatedindroughtmonitoringandearlywarningsystemsand

preparednessplans.

Droughtmustbeconsideredarelative,ratherthan

an absolute, condition. It occurs in both high and

low rainallareas and virtually all climate regimes.

Droughtisotenassociatedonlywitharid,semi-arid

andsub-humidregionsbyscientists,policymakers

and the public. In reality, drought occurs in most

countries,inbothdryandhumidregions.Droughtis

anormalpartoclimate,althoughitsspatialextent

andseveritywillvaryonseasonalandannualtime-scales.Inmanycountries,suchasAustralia,China,

India and the United States o America, drought

occurs over a portion o the country each year.

Owingtotherequentoccurrenceodroughtandthe

proound impacts associated with it, governments

shoulddevotemoreattentiontothedevelopmento

anationalstrategyorpolicytoreduceitseconomic,

social and environmental consequences. A criti-

calcomponentothatstrategyisacomprehensive

drought monitoring system that can provide early

warning odroughts onset and end, determine its

severityanddeliverthatinormationtoabroadclien-

teleinmanyclimate-andwater-sensitivesectorsina

timelymanner.Withthisinormation,theimpactso

droughtcanbereducedoravoidedinmanycases.

Drought is a regional phenomenon and its charac-teristics dier rom one climate regime to another.

Aewexamplesothecontrastingtemperatureand

precipitationregimesovariousregionsareshownin

Figure1.Droughtoccursineachotheselocations,

but characteristics such as requency and duration

vary appreciably. New Delhis precipitation pattern

isdistinctlymonsoonal,withmaximumprecipitation

occurring rom June to October, with the greatest

concentrationinJuly,AugustandSeptember.Tunis

has a distinctly Mediterranean-type (dry summer)

climateregime.Nairobisprecipitationdistributionis

distinctlybi-modal,withpeakrainallexpectedromMarch through Mayanda second concentration in

November and December. Londons precipitation

is evenly distributed throughout the year. In each

example,asignicantdepartureromtheseregimes

oranextendedperiodotimewillresultinimpactsin

climate-andwater-sensitivesectors.Impactsarealso

PhIlIPPEChEvAlIEr(IrD)


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regionalinnature,refectingexposuretothehazard

andthevulnerabilityosocietytoextendedperiods

oprecipitationdecits.Impactsareameasureovul-

nerability.Riskisaproductoexposuretothehazard

andsocietalvulnerability.

Droughtbyitselisnotadisaster.Whetheritbecomes

a disaster depends on its impact on local people,

economiesandtheenvironmentandtheirabilityto

copewithandrecoverromit.Thereore,thekeyto

understandingdroughtistograspitsnaturaland

socialdimensions. The goal odroughtrisk man-

agement is to increase societys coping capacity,

leading to greater resilience and a reduced need

orgovernmentordonorinterventionsintheorm

o disaster assistance. Drought monitoring and

early warning are major components o drought

riskmanagement.

Figure 1. Climographs illustrating monthly temperature and precipitation regimes or New Delhi, Tunis, Nairobi and London.

(Source: National Drought Mitigation Center, University o NebraskaLincoln, USA)

New Delhi

Prec

ipitation(mm) Te

mperature

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JAN FEB MAR A P R MAY JU N JUL A UG S EP O CT N OV D EC

Temperature

Precipitation


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Meteorological

drought

Economic impacts Social impacts

Soil water deficiency

Environmental impacts

Agricultural

drought

Hydrological

drought

Natural climate variability

Increased evaporation

and transpiration

Plant water stress, reduced

biomass and yield

Reduced infiltration, runoff,

deep percolation and

groundwater recharge

Reduced streamflow, inflow to

reservoirs, lakes, and ponds;

reduced wetlands,

wildlife habitat

High temperatures, high winds,

low relative humidity, greater

sunshine, less cloud cover

Precipition deficiency

(amount, intensity, timing)

Time(duration)

DRoUght as a hazaRD:

ConCepts anD DeFInItIons

Droughtdiersromothernaturalhazardsinvari-

ous ways. Drought is a slow-onset natural hazard

thatisotenreerredtoasacreepingphenomenon.

Itisacumulativedepartureromnormalorexpected

precipitation,thatis,along-termmeanoraverage.

This cumulative precipitation decit may build up

quicklyoveraperiodotime,oritmaytakemonths

beore the deciency begins to appear in reduced

streamfows,reservoirlevelsorincreaseddepthto

thegroundwatertable.Owingtothecreepingnature

odrought,itseectsotentakeweeksormonthstoappear(Figure2).Precipitationdecitsgenerally

appearinitiallyasadeciencyinsoilwater;thereore,

agricultureisotentherstsectortobeaected.

Itisotendiculttoknowwhenadroughtbegins.

Likewise, it is also dicult to determine when a

droughtisoverandaccordingtowhatcriteriathis

determinationshouldbemade.Isanendtodrought

heraldedbyareturntonormalprecipitationand,i

so,overwhatperiodotimedoesnormalorabove

normal precipitation need to be sustained or the

droughttobedeclaredociallyover?Sincedrought

represents a cumulative precipitation decit over

anextendedperiodotime,doestheprecipitation

decitneedtobeerasedortheeventtoend?Do

reservoirs and groundwater levels need to return

tonormaloraverageconditions?Impactslingeror

aconsiderableperiodotimeollowingthereturno

normalprecipitation.Thereore,istheendodrought

signalledbymeteorologicalorclimatologicalactors,

or by the diminishing negative impact on human

activitiesandtheenvironment?

Anotheractorthatdistinguishesdroughtromother

naturalhazardsistheabsenceoapreciseanduni-

versallyaccepteddenition.Therearehundredso

denitions,addingtotheconusionabouttheexist-

enceo drought and its degree o severity. Deni-

tions o drought should be region and application

specic or impact specic. Droughts are regional

inextentand,aspreviouslystated,eachregionhas

specicclimaticcharacteristics.Droughtsthatoccur

intheNorthAmericanGreat Plainswilldierrom

Figure 2. Sequence o drought occurrence and impacts or commonly accepted drought types.

All droughts originate rom a defciency o precipitation or meteorological drought but other types o drought and impacts

cascade rom this defciency. (Source: National Drought Mitigation Center, University o NebraskaLincoln, USA)

CArlOSChErEr


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thoseinNortheastBrazil,southernArica,Western

Europe,easternAustraliaortheNorthChinaPlain.

Theamount, seasonality and orm o precipitationdierwidelybetweeneachotheselocations.

Temperature, wind and relative humidity are also

important actors to include in characterizing

drought rom one location to another. Denitions

alsoneedtobeapplicationspecicbecausedrought

impactswillvarybetweensectors.Droughtconjures

dierentmeaningsorwatermanagers,agricultural

producers,hydroelectricpowerplantoperatorsand

wildliebiologists.Evenwithinsectors,therearemany

dierentperspectivesodroughtbecauseimpactsmay

diermarkedly.Forexample,theeectsodroughton crop yield may vary considerably or maize,

wheat, soybeans and sorghum because they are

plantedat dierent times during thegrowingsea-

son and donothave thesamewater requirements

andsensitivitiestowaterandtemperaturestressat

variousgrowthstages.

Drought impacts are non-structural and extend

overalargergeographicalareathandamagesthat

result rom other natural hazards such as foods,

tropical storms and earthquakes. This, combined

withdroughtscreepingnature,makesitparticularly

challenging to quantiy impacts and even more

challenging to provide disaster relie or drought

thanor other natural hazards. These characteris-

tics have hindered the development o accurate,

reliable and timely estimates o the severity and

impacts, such as drought early warning systems

andultimately,theormulationodroughtprepar-edness plans. Similarly, it is dicult or disaster

ocialstaskedwithrespondingtodroughttodeal

withthelargespatialcoverageusuallyassociated

withitsoccurrence.


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types oF DRoUght

Droughtsarecommonlyclassiedbytypeasmeteo-

rological, agricultural, hydrological and socio-

economic.

Meteorological droughtisusuallydenedbyapre-

cipitationdeciencythresholdoverapredetermined

periodotime.Thethresholdchosen,suchas75per

centonormalprecipitation,anddurationperiod,or

example,sixmonths,willvarybylocationaccord-

ingtouserneedsorapplications.Figure3illustrates

threecharacterizationsodroughtorthreedierentcountries based on precipitation departures rom

normal, deciles and the Standardized Precipitation

Index (SPI). Meteorological drought is a natural

eventandresultsrommultiplecauses,whichdier

rom region to region. Agricultural, hydrological

andsocio-economicdrought,however,placegreater

emphasisonthehumanorsocialaspectsodrought,

highlightingtheinteractionorinterplaybetweenthe

natural characteristics o meteorological drought

and human activities that depend on precipitation

toprovideadequatewatersuppliestomeetsocietal

andenvironmentaldemands.

Agricultural droughtisdenedmorecommonlybytheavailabilityosoilwatertosupportcropandor-

age growth than by the departure o normal pre-

cipitationoversomespeciedperiodotime.There

Figure 3. Meteorological drought expressed as percentage departure rom normal precipitation or India, precipitation deciles or

Australia and the Standardized Precipitation Index or Canada. (Sources: Indian Meteorological Department, Australian Bureau o

Meteorology and Prairie Farm Rehabilitation Administration and Agriculture Canada, respectively)


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Figure 4. Interrelationships between meteorological, agricultural,

hydrological and socio-economic drought. (Source: National

Drought Mitigation Center, University o NebraskaLincoln, USA)

Meteorological

Decreasing emphasis on the natural event

(precipitation deficiencies)

Increasing emphasis on water/natural resource managementIncreasing complexity of impacts and conflicts

Time/duration of the event

Agricultural Hydrological

Socio-economic

and political

isno direct relationship between precipitationand

inltration o precipitation into the soil. Inltra-

tionratesvary,dependingonantecedentmoisture

conditions,slope,soil typeandtheintensityo the

precipitation event. Soil characteristics also dier:

somesoilshaveahighwater-holdingcapacitywhile

othersdonot.Thelatteraremorepronetoagricul-

turaldrought.

Hydrological droughtisevenurtherremovedrom

the precipitation deciency since it is normallydened by the departure o surace and subsur-

acewatersuppliesromsomeaverageconditionat

various points in time. Like agricultural drought,

thereisnodirectrelationshipbetweenprecipitation

amountsandthestatusosuraceandsubsurace

watersuppliesinlakes,reservoirs,aquiersandstreams

becausethesehydrologicalsystemcomponentsare

usedormultipleandcompetingpurposes,suchas

irrigation, recreation, tourism, food control, trans-

portation,hydroelectricpowerproduction,domestic

watersupply,protectionoendangeredspeciesand

environmental and ecosystem management andpreservation.There isalsoa considerable time lag

betweendeparturesoprecipitationandthepointat

whichthesedecienciesbecomeevidentinsurace

andsubsuracecomponentsothehydrologicsys-

tem.Recoveryothesecomponentsisslowbecause

olongrechargeperiodsorsuraceandsubsurace

watersupplies.Insomedrought-proneareas,such

as the western United States, snow packaccumu-

latedduringthewintermonthsistheprimarysource

owaterduringthesummer.Reservoirsincreasethe

resilienceothisregiontodroughtbecauseotheir

abilitytostorelargeamountsowaterasabuer

duringsingle-ormulti-yeardroughtevents.

Socio-economic droughtdiersmarkedlyromthe

other types o drought because it refects the

relationship between the supply and demand or

somecommodityoreconomicgood,suchaswater,

livestock orage or hydroelectric power, that is

dependentonprecipitation.Supplyvariesannually

asaunctionoprecipitationorwateravailability.

Demandalsofuctuatesandisotenassociatedwith

apositivetrendasaresultoincreasingpopulation,

developmentorotheractors.

Theinterrelationshipbetweenthesetypesodrought

is illustrated in Figure 4. Agricultural, hydrological

and socio-economic drought occur less requently

thanmeteorologicaldroughtbecauseimpactsinthese

sectorsarerelatedtotheavailabilityosuraceand

subsuracewater supplies. It usually takes several

weeks beore precipitation deciencies begin to

producesoilmoisturedecienciesleadingtostress

on crops, pastures and rangeland. Continued dry

conditionsorseveralmonthsatatimebringabout

a decline in stream fow and reduced reservoir

and lake levels and, potentially, a lowering o the

groundwatertable.Whendroughtconditionspersist

or a period o time, agricultural, hydrological and

socio-economicdroughtoccur,producingassociatedimpacts. During drought, not only are infows to

rechargesurace and subsurace supplies reduced

butdemandortheseresourcesincreasesdramati-

callyaswell.AsshowninFigure4,thedirectlinkage

betweenthemaintypesodroughtandprecipitation

decienciesisreducedbecausewateravailabilityin

suraceandsubsuracesystemsisaectedbyhow

these systems aremanaged. Changes inthe man-

agementothesewatersupplies caneither reduce

oraggravate the impacts odrought.Forexample,

the adoption o appropriate tillage practices and

planting more drought-resistant crop varieties candiminishtheimpactodroughtsignicantlybycon-

servingsoilwaterandreducingtranspiration.


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0

ChaRaCteRIzIng DRoUght anD Its seveRIty

Droughts have three distinguishing eatures: inten-

sity, duration and spatial coverage. Intensity reers

tothedegreeotheprecipitationshortalland/orthe

severityoimpactsassociatedwiththeshortall.Itis

generallymeasuredbythedepartureromnormaloa

climaticparametersuchasprecipitation,anindicator

suchasthereservoirleveloranindexsuchasSPI.

Anotheressentialcharacteristicodroughtisitsdura-

tion.Droughtscan developquickly insomeclimatic

regimes,but usuallyrequire a minimum o two to

threemonthstobecomeestablished.Onceadrought

begins,itcanpersistormonthsoryears.Themag-

nitude odroughtimpacts is closelyrelatedto the

timingotheonsetotheprecipitationshortage,its

intensityandthedurationotheevent.Forexample,

adrywintermayhaveewimpactsinmanymiddle

latitude,temperateclimatesbecauseothereduced

demandorwaterduringthosemonths.Developinga better understanding o the requency, duration

andspatialextentodroughtromthepaleo-record,

or example, tree rings or lake sediments, can be

very instructive because it provides planners with

critically important inormation rom periods out-

sideotheinstrumentalperiodorecord.

Droughts also dierintheirspatial characteristics.

Theareasaectedbyseveredroughtevolvegradu-

ally,andregionsomaximumintensity,suchasepi-

centres,shitromseasontoseasonandyeartoyear

intheeventomulti-yeardroughts.Inlargercoun-tries,suchasBrazil,China,India,theUnitedStates

orAustralia,droughtwouldrarely,iever,aectthe

entirecountry.During1934,oneothemostsevere

droughtyearsinUnitedStateshistory,65percent

o the country was aected by severe or extreme

drought(Figure5).Thatwasthemaximumspatial

extentodroughtbetween1895and2005.

10

30

20

0

40

50

60

70

Figure 5. Percentage o the United States aected by severe to

extreme drought, January 1895 to May 2006.

(Source: National Drought Mitigation Center, University o

NebraskaLincoln, USA; based on data rom the National Climatic

Data Center/NOAA)

PIErrEGAzIN(Ir

D)


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JEAN-PIErrEMO

NTOrOI(IrD)

the Challenges oF DRoUght monItoRIng anD

eaRly WaRnIng

Adroughtearlywarningsystemisdesignedtoiden-

tiy climate and water supply trends and thus to

detectthe emergence orprobability ooccurrence

andthelikelyseverityodrought.Thisinormation

canreduceimpactsideliveredtodecisionmakers

inatimelyandappropriateormatandimitigation

measures and preparedness plans are in place.

Understandingtheunderlyingcausesovulnerability

isalsoanessentialcomponentodroughtmanage-

mentbecausetheultimategoalistoreduceriskora

particularlocationandoraspecicgroupopeopleoreconomicsector.

There are numerous natural drought indicators

thatshouldbemonitoredroutinelytodeterminethe

onset and endo drought andits spatial character-

istics.Severity must also beevaluated on requent

time steps.Althoughalltypesodroughtsoriginate

romaprecipitationdeciency,itisinsucienttorely

solelyonthisclimateelementtoassessseverityand

resultant impacts because o actors identied

previously.Eectivedroughtearlywarningsystems

must integrate precipitation and other climatic

parameterswithwaterinormationsuchasstream

fow, snow pack, groundwater levels, reservoir

andlakelevels,andsoilmoistureintoacompre-

hensiveassessmentocurrentanduturedrought

andwatersupplyconditions.

Monitoring drought presents some unique chal-

lengesbecauseoitsdistinctivecharacteristics.Some

othemostprominentchallengesareasollows:

Meteorologicalandhydrologicaldatanetworks

areoteninadequateintermsothedensityo

stationsorallmajorclimateandwatersupply

parameters. Data quality is also a problem

becauseomissingdataoraninadequatelength

orecord;

Data sharing is inadequate between govern-

ment agencies and research institutions, and

thehighcostodatalimitstheirapplicationin

drought monitoring, preparedness, mitigationandresponse;

Inormation delivered through early warning

systemsisotentootechnicalanddetailed,lim-

itingitsusebydecisionmakers;

Forecastsareotenunreliableontheseasonal

timescale and lack specicity, reducing their

useulnessoragricultureandothersectors;

Droughtindicesaresometimesinadequateor

detectingtheearlyonsetandendodrought;

Drought monitoring systems should be inte-

grated, coupling multiple climate, water and

soilparametersandsocio-economicindicators

toullycharacterizedroughtmagnitude,spatial

extentandpotentialimpact;

Impact assessment methodologies, a critical

parto drought monitoring and early warning

systems,are not standardized orwidely avail-

able,hinderingimpactestimatesandthecrea-

tion o regionally appropriate mitigation and

responseprogrammes;

Deliverysystemsordisseminatingdatatousers

in a timely manner are not well developed,

limitingtheiruseulnessordecisionsupport.


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15/26

consistsoacolourmap,showingwhichpartsothe

UnitedStatesaresueringromvariousdegreeso

drought,andaccompanyingtext.Thetextdescribes

the droughts present impacts, uture threats and

prospectsorimprovement.USDMisbyarthemost

user riendly national drought monitoring product

availableintheUnitedStatestoday.TheInternetis

currentlytheprimarydistributionvehicle,although

themapalsoappearsinlocalandnationalnewspa-persandontelevision.Figure7illustratesthepat-

ternodroughtconditionsacrosstheUnitedStates

rom2002to2005.Asingleweeklymapillustrates

the drought pattern in each year. All USDM maps

since1999arearchivedonthewebsiteandavailable

tousersorcomparison.

Sincenosingledenitionodroughtisappropriate

inallsituations,agriculturalandwaterplannersand

othersmustrelyonavarietyodataorindicesthat

areexpressedinmaporgraphicorm.TheUSDM

authorsrely onseveral key indicators and indices,

suchasthePalmerDroughtSeverityIndex(PDSI),the Standardized Precipitation Index, stream fow,

vegetationhealth,soilmoistureandimpacts.Ancil-

lary indicators such as the Keetch-Byram Drought

Index,reservoirlevels,SuraceWaterSupplyIndex,

Figure 7. Spatial extent and severity o drought conditions in the United States, 2002 to 2005 , as per the US Drought Monitor.(Source: http://www.drought.unl.edu/dm)


16/26

riverbasinsnowwaterequivalent,andpastureand

range conditions rom dierent agencies are inte-

gratedtocreatethenalmap.Electronicdistribution

oearlydratsothemaptoeldexpertsthroughout

thecountryprovidesexcellentgroundtruthorthe

patterns and severity o drought illustrated onthe

mapeachweek.

USDMclassiesdroughtsonascaleromonetoour

(D1D4),withD4 refectinganexceptionaldrought

eventsuchasa1in50-yearevent.Athcategory,D0, indicates an abnormally dry area. The USDM

map and narrative identiy general drought areas,

labelling droughts by intensity rom least to most

intense.D0areasareeitherheadingintodroughtor

recovering rom drought but still experiencing lin-

geringimpacts.

USDMalsoshowswhichsectorsarepresentlyex-

periencing direct and indirect impacts, using the

labels A (agriculture:crops, livestock,pasture and

grasslands), and H (hydrological) and/or W (water

supplies).Forexample,anareashadedandlabelledasD2(A)isingeneralexperiencingseveredrought

conditionsthatareaectingtheagriculturalsector

moresignicantlythanthewatersupplysector.The

mapauthorsarecareulnottobringanareaintoor

out o drought too quickly, recognizing the slow-

onset characteristicso drought,the longrecovery

processandthepotentialorlingeringimpacts.

The methodology associated with USDM has now

beenappliedtotheproductionotheNorthAmerican

Drought Monitor (NADM), a collaborative project

between the United States, Mexico and Canada.

Thepartnershipbeganin2002inanattempttomapdrought severity and spatial patterns across the

North American continent. Figure 8 illustrates the

NADM or May 2006. Multiple indices and indica-

torsareusedtomapdroughtconditions,similarto

theprocedureusedtogeneratetheUSDM.Respon-

sibility or this product is shared between NOAAs

National Climatic Data Center, the US Department

o Agriculture andthe National Drought Mitigation

CenterattheUniversityoNebraskaLincolninthe

United States; the National Water Commission in

Mexico; and Environment Canada and Agriculture

andAgri-FoodCanada.Thisproductispreparedonamonthlybasisandisanexcellentexampleointer-

nationaldroughtmonitoringcooperation.

Figure 8. North American Drought Monitor, May 2006. (Source: North American Drought Monitor,

http://www.ncdc.noaa.gov/oa/climate/monitoring/drought/nadm/index.html)


17/26


18/26


19/26

IGaD ClImaTe PreDICTIon anD aPPlICaTIons

CenTre (ICPaC)

The Greater Horn o Arica, like many parts o the

tropics,isprone toextreme climateevents such as

droughts and foods. In an eort to minimize the

negative impacts o extreme climate events, WMOand the United Nations Development Programme

established theregionalDrought Monitoring Centre

(DMC)inNairobiandasub-centreinHararein1989

covering 24 countries in the eastern and southern

Aricansubregion.In2003,DMCNairobibecameaspe-

cializedinstitutionotheIntergovernmentalAuthority

onDevelopment(IGAD)andwasrenamedtheIGAD

ClimatePredictionand ApplicationsCentre( ICPAC).

The participating countries o ICPAC are Burundi,

Djibouti, Eritrea, Ethiopia, Kenya,Rwanda,Somalia,

Sudan,UgandaandUnitedRepublicoTanzania.The

Centreisresponsibleorclimatemonitoring,predic-

tion,earlywarningandapplicationsorthereductionoclimate-relatedrisksintheGreaterHornoArica.

ICPACsmainobjectiveistocontributetoclimatemoni-

toring and prediction services or early warning and

mitigation othe adverseimpactsoextremeclimate

eventsonvarioussocio-economicsectorsintheregion,

suchasagriculturalproductionandoodsecurity,water

resources,energyandhealth.Theearlywarningprod-

uctsenableuserstoputmechanismsinplaceorcoping

withextremeclimate-andweather-relatedrisksinthe

Greater Horn o Arica. The Centre also promotes

capacity-buildingorbothclimatescientistsandusers.

ICPACprovidesregularregionalclimateadvisories,

including10-day,monthlyandseasonalclimatebul-

letinsaswellastimelyearlywarninginormationon

evolvingclimateextremesandassociatedimpacts.

Regional Climate Outlook Forums are also being

heldbeoretheonsetothemajorrainallseasonsto

provideconsensusclimateoutlooksandtodevelop

mitigationstrategies.Belowaresomeotheactivi-

tiesundertakenbyICPAC:

Development and archiving o regional andnationalquality-controlledclimatedatabanks;

Data processing, including development o

basicclimatologicalstatistics;

Timelyacquisitiononearreal-timeclimateand

remotelysenseddata;

Monitoring space-time evolutions o weather

andclimateextremesovertheregion;

Generationoclimatepredictionandearlywarn-

ingproducts;

Delineation o risk zones o extreme climate-

relatedevents;

Timelydisseminationoearlywarningproducts;

Conducting capacity-building activities in the

generationandapplicationoclimateproducts;

Organizationoclimateoutlookorumsorthe

countriesintheGreaterHornoArica;

Enhancementointeractionswithusersthrough

userworkshopsandpilotapplicationprojects;

Climate change monitoring, detection and

attribution.


20/26

Figures 12 to 14 illustrate a range o climate- and

drought-relatedproductsproducedbyICPAC(http://

www.icpac.net). The products depict cumulative

rainall deviations rom the mean or Marsabit,

Kenya;aregionalclimateoutlookmap;andamap

illustrating the ood security outlook or the coun-

triesintheGreaterHornoArica,respectively.

Mean

2005/2006

35

45

20

33

33

33

20

45

35

20

4535

35

45

20

33

33

33

35

45

20

I

II

IV

V

VI

VII

VIII

III

Sudan

Rwanda

Uganda

Burundi

Ethopia

Somalia

Kenya

United Republicof Tanzania

Eritrea

Djibouti

Figure 12. Examples o cumulative decadal rainall over parts o Kenya rom June 2005 to early April 2006 . (Source: ICPAC)

Cumulativerainfall(mm)

Marsabit, Kenya

DecadsJUN1 JUN3 JUL2 AUG1 AUG3 SEP2 OCT1 OCT3 NOV2 DEC1 DEC3 JAN2 FEB1 FEB3 MAR2 APR1 APR3 MAY2

0

100

200

300

400

500

600

700

800

900

Figure 13. Climate outlook or the Greater Horn o Arica,

March to May 2006. (Source: ICPAC)

Figure 14. Food security outlook or the Greater Horn o Arica,

September to December 2005. ( ICPAC)

A Above normal

N Normal

B Below normal

Percentage probability

Extremely food insecure

Highly food insecure

Moderately food insecure


21/26

souTh aFrICa

Droughtisanormal,recurrenteatureotheSouth

Aricanclimate.Droughtshaveinthepastresulted

in signicant economic, environmental and social

impactsandhighlightthecountryscontinuingvul-

nerabilitywithregardtothisnaturalphenomenon.

During low rainall periods, policymakers, agricul-

turalists, businesses and the general public oten

requireadditionalrainalldataordecision-making

andplanning.

InresponsetorecurringdroughtinSouthArica,the

SouthAricanWeatherService(SAWS)establisheda

droughtmonitoringdeskwhereinormationregard-

ingobservedrainallandlong-rangeorecastscould

be presented in one place or easy access. It also

provides anopportunityor people to comparethe

current years rainall with amounts rom previous

dryperiodstoassistthemintheirdecisionandplan-

ningpractices.

Neither the percentage o normal nor the decile-

based drought indices can assist decision makers

with the assessment o the cumulative eect o

reducedrainall overvarious timeperiods.Neither

otheseindicescandescribe themagnitudeo thedrought compared with other drought events. SPI

can alleviate both o these principal shortcomings

while atthesametime being less complex to cal-

culatethansomeotheotherdroughtindicesnow

inuseattheSouthAricanWeather Service.SPIis

anindexbasedontheprobabilityorainallorany

timescale;itcanbeuseulinassessingtheseverity

o drought and can be calculated at various time-

scalesthatrefecttheimpactothedroughtonthe

availabilityowaterresources.TheSPIcalculationis

based onthedistributiono rainalloverlong time

periods, preerably more than 50 years. The long-termrainallrecordisttoaprobabilitydistribution,

whichisthennormalizedsothatthemeanSPIor

anyplaceandtimeperiodiszero.SPIvaluesabove

zero indicate wetter periods and values less than

zeroindicatedrierperiods.

On23November2005,theDepartmentoAgriculture

issuedareportindicatingthateightoSouthAricas

nine provinces were being severely aected by

drought,theexceptionbeingthedenselypopulated

Gautengprovince,aminorplayerinagriculture.At

thattime,thenorthernmostprovince,Limpopo,had

had districts fagged as disaster areas since 2003and2004,with27oits37municipalitiesaected.

Thedamsotheprovincewereattheirlowestlevels,

anaverageo36percentocapacity,comparedwith

64percentthepreviousyear.

Theseverityothesituationwasclearlyrefectedin

thedierenttimescalesotheSPImapsontheSAWS

Drought Monitoring Page (http://www.weathersa.

co.za/DroughtMonitor/DMDesk.jsp),updatedatthe

beginningoDecember2005.Averydrywinterand

the lack o good spring rains exacerbated the dry

conditionsinsomeareas.

ThemainrainalleaturesinNovember2005werenear

normalrainallovermostoSouthArica,butwetcondi-

tionsoverpartsotheWesternCape,theEasternCape,FElIxMASI/vO

ICElESSChIlDrEN,COurTESYOFPhOTOShArE


22/26

0

KwaZulu-Natal and Mpumalanga (Figure 15, top).

Accordingto availabledata,nopart othecountry

received rainall much below the normalvalue or

themonth.

FromSeptembertoNovember2005,therewassome

alleviation o the dry conditions in the northern

provincesaswellasthearsouth(Figure15,middle).

However,somedrynessremainedinthenorthernmost

province,Limpopo.

Therainallorthesix-monthperiod,asshownby

theSPImaporJunetoNovember2005,showsnear

normal conditions over the largest part o South

Arica,butmoderatetoverydryconditionsinseveral

areas, most notably in the Southern Cape, southern

partsotheNorthernCapeandthearnorth(Figure15,

bottom).EventhoughsomepartsoLimpoporeceived

good rains during November 2005, there was still a

strainonwaterresources.

PorTuGal

ThePalmerDroughtSeverityIndexisusedtochar-

acterize drought in Portugal. This index has been

adaptedandcalibratedtothespecicclimaticcon-

ditions omainland Portugal.The PDSI perormsa

parameterizedcomputationothesoilwaterbalance

andcomparestheestimatedsoilmoisturecontent

withitsclimatologicalmean.

Evolving drought patternsare presented in monthly

PDSImapsthatshowthespatialdistributionodrought

in Portugal. These mapsare used tomonitor spatial

and temporal variations in droughtacross mainlandPortugal,whichishelpulindelineatingpotentialdis-

asterareasoragricultureandothersectors,allowing

orimprovedon-armdecisionstoreduceimpacts.

The20042005hydrologicalyearbeganwithavour-

ableamountsoprecipitationinOctober,exceptin

the southern region, where it was dry to normal.

The months that ollowed were dry to extremely

dry,resultinginthedevelopmentoaveryintense

drought. Figure 16 and Table 1 show the monthly

PDSI variations expressed as percentages o area

aected in mainland Portugal. In addition, theyrevealadeteriorationodroughtconditionsduring

thewintermonths,withsomeattenuationinMarch

because o the occurrence o precipitation in the

countrysnorthernandinnerregions.DuringJune,

Figure 15. Standardized Precipitation Index (SPI) or South Arica,

November 2005 (top); September to November 2005 (middle); June to

November 2005 (bottom). (Source: South Arican Weather Service)

Extreme drought

Severe drought

Moderate drought

Mild drought


23/26

Palmer Drought

Severity Index

(PDSI)

a ctd by dgt i 20042005 (p ct)

2004 2005

31

Oct

30

Nov

31

Dec

31

Jan

28

Feb

31

March

30

April

31

May

30

June

31

July

31

Aug

30

Sept

31

Oct

30

Nov

31

Dec

mdty wt 5 0 0 0 0 0 0 0 0 0 0 0 0 0 0

sigty wt 47 0 0 0 0 0 0 0 0 0 0 0 6 5 5

n 22 1 0 0 0 0 0 0 0 0 0 0 6 12 11

mid dgt 20 47 30 0 0 26 15 4 0 0 0 0 52 81 83

mdt dgt 5 47 48 25 23 22 22 28 3 0 0 3 36 2 1

sv dgt 1 5 20 53 44 28 20 20 33 27 29 36 0 0 0

ext dgt 0 0 2 22 33 24 43 48 64 73 71 61 0 0 0

July and August, the drought situation worsened.

Thesemonthsnormallycontribute,onaverage,only

6percentotheannualprecipitation.Precipitation

Table 1. Percentage o mainland Portugal aected by drought in 2004 and 2005 . (Source: Instituto de Meteorologia, I.P., Portugal)

Percentage

of

country

OCT-04

0

100

20

NOV-04 DEC-0 4 JAN-05 FEB-05 MAR- 05 APR- 05 MAY- 05 JUN-0 5 JUL-05 AUG-05 SEP-05 OCT-0 5 NOV- 05

40

60

80

DEC-05

Figure 16. Percentage o Portugal aected by drought, October 2004 to December 2005. ( Source: Instituto de Meteorologia, I.P., Portugal)

Extreme drought

Severe drought

Moderate drought

Mild drought

Normal

Slightly wet

Moderately wet

Very wet

Extremely wet

received during the rst 15 days o September

lessenedtheseverityodroughtinthenorthernand

centralregions.


24/26

Period

actd ppti

With

supplemented

water

With

cuts/reduction

insupply

1t api 14175 213

1t my 8395 2635

1t J 26500 26781

2d J 23440 25217

1t Jy 26004 26350

2d Jy 54831 53312

1t agt 48500 60061

2d agt 94372 100500

1t sptb 73097 66127

2d sptb 69588 39429

2d octb 48883 30083

2d nvb 11921 13354

2d Dcb 10238 13445

mxi 94 372 100 500

Table 2. Number o people aected directly or indirectly by drought

in Portugal, 2005. ( Source: Instituto de Meteorologia, I.P., Portugal)

Figure 18. Number o municipalities with supplemented water (blue) or cuts/reduction in household supply (red). (Source: Instituto de

Meteorologia, I.P., Portugal)

Figure 17. Spatial representation o consecutive months in severe

and extreme drought situations in Portugal, October 2004 to

September 2005 . (Source: Instituto de Meteorologia, I.P., Portugal)

Figure17showsthenumberoconsecutivemonths

insevereandextremedroughtthroughtheendo

September2005.

Theimpactsothedroughtonagriculture,energyand

urbanwatersupplywere signicant.Figure18illus-

tratestheseimpactsontheurbanwatersupply.The

numberopeopleaectedbydroughtromAprilto

December2005,asshowninTable2,isalsoagood

indicatorothewidespreadimpactsassociatedwith

thisdroughtevent.

Numberofmunicipalities

15 MAR

0

70

10

15 APR 15 MAY 15 JUN 30 JUN 15 JUL 31 JUL 15 AUG 31 AUG 15 SEP 30 SEP 31 OCT 30 NOV 31 DEC

20

30

40

50

60

Municipalities with supplemented water

Municipalities with cuts/reduction in water supply


25/26

Figure 19. The extent o serious or worst rainall defciencies at the

peak o the last El Nio-related drought in 2002 and 2003.

(Source: Australian Bureau o Meteorology)

thepeako the lastElNio-relateddrought during

20022003.

Althoughanextendedperiodorainalldeciencyin

anyareaisvirtuallyaprerequisiteordrought,there

iswidespreadrecognitioninAustraliathattheormal

declaration o a drought is a more complex issue.

It involves consideration not only o the rainwater

supplybutalsothesubsequentusesorthatrainall

onceithasallenontoarmlands,runsintostreams

andrivers,isstoredindams,isusedtodrivehydro-electricpowerstationsandissuppliedtocitiesand

townsacrossthenation.Furthermore,giventhesize

andgeographicallocationoAustralia,itisunusual

ortherenottobeoneormoreareasovaryingsize

at any given time experiencing serious or severe

rainalldeciencies.Whetherornotsuchareasare

declared drought stricken and then whether the

droughtisosucientintensity,durationandextent

orthoseaectedtobeeligibleorgovernmentrelie

involvesacomplexseriesoassessmentsbynational

andstateauthorities.

The recognition that drought is a normal eature

oAustraliasnatural,economic,andsocialenviron-

mentshasledthenationalandstategovernmentsto

agreethatclimate-sensitiveindustriesandenterpris-

esmustlearntomanagedroughtrisk,alongwithall

theotherattendantandongoingrisksthattheyace.

Nonetheless, the governments do recognize that,

romtimetotime,somedroughtsbecomesosevere,

chronicor widespread that thereis a need to oer

supporttothoseworstaected.Suchoccurrencesin

Australiaarecalledexceptionalcircumstances.

In 20022003 Australia experienced an especiallysevere and widespread drought, accompanied by

recordhightemperaturesinmanyregions.Atthepeak

othedrought,57percentotheAustralianmainland

hadregistered10monthsormoreoserioustosevere

cumulativerainalldecits,and90percent,belowthe

median(Figure19).Withtheexperienceothedrought

reshinmind,andalsorecognizingtheneedoramore

objective, airandtransparent processunderpinning

the declaration o exceptional circumstances, the

Primary IndustriesMinisterial Councilo Australiain

2005commissionedtheestablishmentotheNational

AgriculturalMonitoringSystem(NAMS).

NAMSwasdevelopedoverthenext12monthsunder

the leadership o the Bureau o Rural Sciences in

collaboration with the Bureau o Meteorology and

ausTralIa

TheislandcontinentoAustraliastraddlesthesouth-

ern subtropical zone, with its mainland extending

romaround11SacrosstheTopEndto39Sin

thesouth-east.Thenorthernregionsareseasonally

tropicalwhiletheeastern,south-easternandsouth-

westerncoastsandnearinlandregionsaregener-

allywellwateredbutpronetohighinterannualand

seasonalvariabilityintheirrainall.Themoreinland

regions range rom arid to semi-arid. Droughts,sometimes covering vast tracts o the continent,

arearecurringeatureoAustraliasclimate.Many

o the more severe and widespread droughts are

associatedwithElNioevents.

Given that rainall is by ar the dominant actor

determiningthesuccessorailureothegrowing

seasonacrossAustralia,droughtmonitoringhasor

many years been synonymous with the monitor-

ingorainalldeciencies.TheAustralianBureauo

MeteorologysDroughtWatchService,inoperation

since1965,hasusedaccumulatedrainallpercentilesoversuccessivemonthstoidentiyregionsorainall

decitandexcess.Areaswithrainallaccumulations

belowthe10thor5thpercentileorperiodsothree

monthsormorearereerredtoasbeingseriously

orseverelyindecit,respectively.Figure19shows

theextentoseriousorworserainalldecienciesat

ri dfcici: 10 t

1 api 2002 t 31 Jy 2003Distributionbasedongriddeddata

ProductotheNationalClimateCentre

Serious deficiency

Severe deficiency

Lowest on record

Rainfall percentile ranking


26/26

Droughtaectsmorepeoplethananyothernatural

disasterandresultsinseriouseconomic,socialand

environmental costs. The development o eective

drought monitoring, early warning and delivery

systems has been a signicant challenge because

otheunique characteristics odrought. Signicant

strideshavebeenmadeinrecentyearstoimprovethe

eectivenessothesesystems.Withtheincreasing

requencyandseverityodroughtinmanyregionso

theworldandincreasedsocietalvulnerability,more

emphasisisnowbeingplacedonthedevelopmentodroughtpreparednessplansthatareproactiverather

thanreactiveandemphasizerisk-basedmanagement

measures. Improved drought monitoring is a key

component o a drought preparedness plan and a

nationaldrought policy. Early warning systems can

provide decision makers with timely and reliable

accesstoinormationonwhichmitigationmeasures

canbebased.Therearemanychallengestoimprov-

ing thesesystems, buta comprehensive,integrated

approachtoclimateandwatersupplymonitoring is

provingtobesuccessulinmanycountries.

theCommonwealthScienticandIndustrialResearch

Organization(CSIRO).Theoutcomeisareelyacces-

sible websitecontaining currentmaps, graphs and

reports on the state o the climate system across

Australia,andinormationonproductionormajor

drylandbroad-acreagriculturalsystems.Aswellas

currentdata,NAMSalsocontainshistoricalinorma-

tion onmeasuredand modelled production,nan-

cialimpacts,remote-sensingindicesandclimate.

TheNAMSwebsitepresentsinormationonscreenandintheormoprintablereports,providinggen-

eral background, current climatic conditions and

production and resource statistics or regions that

canbespeciedbytheuser.Regionscanrangein

sizeromtheentirecountrytoindividuallocalgov-

ernmentareasorthestatisticallocalareasusedor

summarizingAustraliancensusdata.

Collectively, NAMS inormation shows the status

o current conditions or the major agricultural

production systems and production prospects or

the upcoming growing season. NAMS is initiallydirectedatmonitoringandsupplyingdataordry-

landbroad-acreindustries,withplanstoextendthe

system to cover the extensive irrigated regions o

Australiaandalsoormoreintensiveindustriessuch

ashorticulture.

AsNAMSdrawsonacommoninormationdatabase

or theentirecountry, it will acilitatea more con-

sistentapproachtothedroughtdeclarationprocess

throughtheuseotheollowing:

Acommontemplateandlanguageordescrib-

ingdroughtintermsoprobabilities;

Acommonsetodeclarationcriteria;

A common process or the subjective on-

groundassessmentodroughtimpacts.

The NAMS website is at http://www.nams.gov.au.

DetailedinormationonAustraliasnationaldrought

assistance measures, including the declaration o

exceptional circumstances, can be ound at http://

www.da.gov.au/droughtassist, while inormation

ontherainalldeciencymonitoringsystemcanbeound at http://www.bom.gov.au/climate/drought/

drought.shtml.

ConClUsIon

Documents

Drought monitoring and early warning: concepts, progress and future challenges