The EDDI User Guidev1.0 – September 2017

Jeff Lukas, Mike Hobbins, Imtiaz Rangwala and the EDDI team

Contents- UseBookmarks inPDFtonavigate1) Cover2) Contents3) Theintendedaudience4) WhatthisUserGuideprovides5) EDDIinanutshell6) KeyfeaturesofEDDI7) WhatEDDIisnot8) Drought=moisture imbalance9) AboutEvaporativeDemand(E0)10) NormalE0 variesacrosstheUS11) Largeseasonalcycle inE012) TherelationshipbetweenETandE013) HighE0=surfacemoisturestress14) IncreasingE0reflectsdroughtintensification15) HowEDDIiscalculated16) EDDIcategories17) Seasonalinterpretation ofEDDI18) EDDIcomparedwithotherindicators19) EDDIcomparedwithotherindicators20) Comparingdifferentindicators21) Convergenceofevidence fordrought22) BasicsofreadinganEDDImap23) InterpretingEDDIatdifferenttimescales24) InterpretingEDDIatdifferenttimescales25) EDDIgivesearlywarningofflashdrought

26) Moreflashdroughtearly-warning27) NotallEDDIhotspotsbecomedrought28) EDDIinagricultural droughtmonitoring29) Potentialapplicationsinfire&hydrology30) DecomposingE0toseedroughtdrivers31) Wheretogetcurrent EDDImaps32) Wheretogetpast EDDImaps33) WheretogetEDDItime-series34) Technical backgroundonEDDI35) Acknowledgements

2

ThisUserGuideisintendedfor:• Managers: Thosewhomonitordrought

conditions inordertomanageresourcesandmakedecisions;e.g.,agproducers,andwater,fire,forests,range,andwildlifemanagers

• Translators:Thosewhoworkcloselywiththeabovegroups inanadvisoryoroutreachroleand/ordisseminatedrought information;e.g.,NWSforecasters,Stateclimatologists,droughtcoordinators

• Researchers: Thosewhostudythedroughtphenomenon tobetterunderstand itscauses,manifestations,andimpacts

• Thelevelofinformation intheGuideismostsuitedforthefirsttwogroups.Butresearchersmayfind theoverviewusefulbeforedelvingmoreintothetechnicalbackground onEDDI. 3

WhatthisUserGuideprovidesClearandconciseexplanationsof:

• EvaporativeDemand (E0)andwhyitisimportanttodrought

• HowEDDIiscalculatedandhowitdepictsEvaporativeDemand

• HowEDDIrelatestootherdrought indicators

• HowtointerpretEDDImapsoverdifferent timewindows

ThisUserGuidewillbeupdatedbasedonuserfeedback.Pleaseletusknowifitwashelpful,andhowitmightbeimproved.

SendfeedbacktoJeffLukas,lukas@colorado.edu4

EDDIinanutshell

• EDDIisadrought indexbasedonthe“thirst”oftheatmosphere—whichleadstothedrying ofsoilsandvegetation,andalsoreflectsthatdrying

• Moretechnically:EDDIshowstheanomaly*indailyevaporativedemandaggregatedoveraspecified timewindow,atagivenlocation

• EDDIiscalculatedfromobservationsoftheatmospherenearthelandsurface:temperature,humidity, windspeed,andsolarradiation

• EDDIcanprovideaddedvaluetootherdrought indicators,especiallyforearlywarningandflashdroughtdetection

*i.e.,theunusualness ofthecurrentconditionsascomparedtotherangeofhistorical conditions 5

KeyfeaturesofEDDI

• EDDImapsareproduced innear-real-time,witha~5-daylag

• EDDIiscalculatedovermultiple timewindows(like theStandardizedPrecipitationIndex;SPI),tosuitdifferentapplications

• EDDImapshaveaspatialresolutionof1/8-degree(~12kmor~7miles)

• EDDIusesaclassificationschemethatisequivalenttotheUSDroughtMonitorcategories(D0,D1,D2,etc.)

• EDDIisnotsensitivetotheland-covertype,soitisappropriate foruseinallregions

6

WhatEDDIisnot

• EDDIdoesn’tdirectlymeasureon-the-ground conditions—thoughEDDIvaluesarestronglyinfluencedbysurfacemoistureconditions

• EDDIisnotadroughtprediction,butatshorttimescales,itindicatesthepotential fordroughtemergence

• EDDIisnotameasureofactualevapotranspiration (i.e.,ET)

7

Droughtresultsfrommoistureimbalanceatthelandsurface

RUNOFF

PRECIPITATION

ETE0

• Themoisturestatusatthelandsurfacereflectsthebalanceofgainsfromprecipitation andlossesfromevapotranspiration (ET)

• Drought (inadequatesurfacemoisture) istypicallyinitiatedbybelow-normalprecipitation(reducedgains),andworsened byabove-normalevaporativedemand (increasedlosses)

• ETistherateofactualmoisturelosstotheatmosphere,usuallyexpressedasin./dayormm/day,fromsoils,openwater,and/orvegetationatonelocation

• ETiscoupled toevaporativedemand(E0) butunlikeE0,ET isconstrainedbythesurfacemoisturesupply

• ETcanneverexceedE0,andisoftenless 8

Evaporativedemand(E0)isthe“thirstoftheatmosphere”

fao.org

• E0 istheETthatwouldoccurgivenanunlimitedsurfacemoisturesupply

• E0 iseasiertoquantify thanET

• E0 canestimatedbyoneofseveralmethods:

o ReferenceET(ET0)o PotentialET(PET)o Panevaporation

• AccurateestimatesofReferenceET,suchasusedinEDDI,requirethesevariables:

o Temperatureo Humidityo Windspeedo Solarradiation

9

MeanannualE0 (mm),1981-2010

The“normal”E0 varieswidelyfromplacetoplace,withhigherE0indryandhotplaceslikewestTexas,andlowerE0incoolandwetplaceslikeMaine

The mean annual E0 varies by a factor of ~3 between the dry-hot Southwest and the cool-wet Northeast

Figure: Mike Hobbins, adapted from Hobbins (2016), Trans. ABABE

10

E0hasalargeseasonalcycle,peakinginthesummer

Daily E0 for the Midwest US (1980-2016), with summer values highlighted

• WhenE0 inthesummer isevenhigher thanusual(asin2012,below) itoftenreflectstheonsetorrapidintensificationofdroughtconditions

11

Time

Surface moisture availability

Evapotranspiration(ET)

Evaporative Demand(E0)

Moisture is notlimitingET ~ E0

Moisture is limiting E0 > ET

Feedback from the drying land surface increases E0

TherelationshipbetweenE0 andET changesasthelandsurfacedriesout

• Whensufficient surfacemoistureisavailable,risingE0 leadstorisingET

• Whenmoisture islimited,ET declines,whileE0 risesevenmoresteeply

• Regionswithamorearidclimate(yellowandredbelow)areoften inthemoisture-limitedstateunder ‘normal’ conditions

12

Inotherwords:Unusuallyhighevaporativedemand(E0)canleadtomoisturestressonthelandsurface,andultimatelytodrought—evenwhenprecipitationhasbeennear-normal

E0

ET

Soil Moisture

13

Oncedroughthasdeveloped,thenow-drylandsurfacemakestheairabovethesurfacewarmeranddrier—whichfurtherincreasesevaporative demand

E0

ET

Soil Moisture

14

HowEDDIiscalculated

Startwithmeteorologicalinputs foreachgridcell(temperature,humidity,windspeed, solarradiation)

fromNLDAS-2,1/8-degreegriddedmetdata

CalculatedailyReferenceET(ET0;estimateofE0)andaggregateitovertheselectedtimewindowusingtheASCEvariantofthePenman-Monteith equation*

DeterminewherethataggregatedE0 valueslotsintotheclimatology(1980-present) foreachgridcell

usingrank-basednon-parametricprobabilities

Higher E0than normal

Lower E0 than normal

Temperature

Humidity Wind speed

Radiation

Temperature Humidity

Wind speed

Radiation

*identicaltotheFA056variantofthePenman-Monteith atdailytimescales

EDDI15

100th2 5 10 20 30 70 80 90 95 98Percentile

ED0 ED1 ED2 34 ED0ED1ED23 4EDDI Category 4

Onthedryend,EDDIusesthesamepercentilebreaksasintheUSDroughtMonitor

Higher E0than normal

Lower E0 than normal

EDDIcategoriesarederivedfromthedistributionofaggregatedE0values;selectedpercentilesusedasthresholdsforthecategories

ObserveddistributionofE0from1980-present forthegivenlocationandtimewindow

16

Inthesummer,anygivenEDDIcategorywillreflectamuchlargeraggregatedE0 valuethaninotherseasons

• SowhenEDDIisinadrought categoryduring thesummer, thedroughtimpactsaregenerallygreaterthanduring thecoolerseasons

• Thatsaid,emergenceofED3orED4inotherseasonscanstillindicatehigh riskof significantimpacts,suchaswildfires (below,Sunshine Fire)

Daily E0 for Boulder, CO, with 30-day running mean (2009-2017)

2010 2011 2012 2013 2014 2015 2016 2017

June 25, 2012 – Flagstaff Fire 1-month EDDI: ED4

March 19, 2017 – Sunshine Fire 1-month EDDI: ED4

17

HowthephysicalbasisofEDDIcompareswithotherdroughtindicators- partI

E0

EDDIAnomalyinestimatedEvaporativeDemand(E0)overauser-selectedtimewindow,whereE0isestimatedfromobservedTemperature,Humidity,Windspeed,andsolarRadiation

SPI(StandardizedPrecipitationIndex)AnomalyinobservedPrecipitation(P)overauser-selectedtimewindow ofinterestP

SPEI(StandardizedPrecipitation-EvapotranspirationIndex)Anomalyinthedifferencebetween observed Precipitation(P)andestimatedPotentialEvapotranspiration(PET;equivalentto E0*)overauser-selectedtimewindow

P

PDSI(PalmerDroughtSeverityIndex)Simulatedsoil-moisturebalanceanomaly,calculatedfromobservedPrecipitation(P)andanestimateofE0*,withaneffectivetimewindow of~6-12months

P

*SomesourcesofSPEIandPDSImapsanddatauseafullyphysicalestimateofE0;othersusearoughestimateofE0fromTemperatureonly

E0

E0

18

E0

EDDIAnomalyinestimatedEvaporativeDemand(E0)overauser-selectedtimewindow,whereE0isestimatedfromobservedTemperature,Humidity,Windspeed,andsolarRadiation

ESI(EvaporativeStressIndex)AnomalyintheratioofETtoE0,whereETiscalculatedusingleaf-areaindex(LAI)andland-surfaceTemperaturefromsatellitedata,andE0isfromafullyphysicalestimate,overauser-selectedtimewindow

USDM (U.S.DroughtMonitor)Quasi-objectiveblendofmultipledroughtindicators:SPI,PalmerIndices,modeledsoilmoisture,observedstreamflow,reporteddrought impacts,andother indicators;inherenttimewindow variesbyseason/region

P

P

ET

VegDRIBlendofmultipledroughtindicators:9-monthSPI,PalmerIndex,andsatellite-sensedvegetationgreennessandleaf-outanomaly;effectivetimewindowofseveralmonthsvegetation

HowthephysicalbasisofEDDIcompareswithotherdroughtindicators- partII

T (~E0)

E0

T (~E0)

19

It'sgoodpracticetocomparedifferentdroughtindicators

E0(T)

PE0(T)

P

E0(T)ET

vegetation

E0

E0(T)

P

PE0(T)

P

• EDDIandtheotherindicatorscapturedifferentaspectsofthemoisturebalanceatthelandsurface;EDDIisunique infocusingonevaporativedemand

• Differentindicatorsalsohavedifferent timewindowsoverwhichconditionsareaggregated—whether thewindowisuser-selectedor“bakedinto”thatindex

• Thus,different indicatorscanspeaktosomedroughtimpactsbetterthanothers

• Lookingatmultipleindicatorsprovidesa“convergenceofevidence”,e.g.,tosupportadrought designation

• Thedifferencesbetweenindicatorscanalsoprovideinsight intohowdroughtconditionsareemergingandcausingimpacts

20

Forexample,the3-monthEDDIforMay-July2002showsadroughtpatternverysimilartootherindicatorsusedforagricultural droughtimpacts(“convergenceofevidence”)

July 31, 2002

USDM 3-month EDDI

VIC-modeled Soil Moisture 3-month Evaporative Stress Index (ESI)

21

ThebasicsofreadinganEDDImapAn“EDDImonth”is30days,sothis3-monthmapisbasedonevaporativedemandfromFebruary4toMay4,2017(90days).

ThemostrecentEDDImapslagthecurrentdateby~5days—sothismapwasreleasedaroundMay9,2017

Evaporativedemandwasunusuallyhigh forFeb4-May4intheOhioValley,Florida,andthewesternGreatPlains.(ED4meansthatconditionsthisdryareexpected inonly2%ofFeb4-May4periods.)

Evaporativedemandwasunusuallylow forFeb4-May4inthePacificNorthwestintotheRockies.

Thenames,colors,andpercentile breaksforthedroughtcategoriesareanalogoustothosefortheUSDroughtMonitor.

TheDroughtandWetnesscategoriesforagivennumberhavethesameexpected frequency(e.g.,ED2andEW2). 22

2-weekEDDI12-monthEDDI

InterpretingEDDIatdifferenttimescalesThesimpleversion:Long-term(>3-month)= droughthasemergedorispersistingShort-term (2-weekto3-month)=potential fordrought emergence/intensification

Unusuallyhighevaporativedemandoverpast12monthsinsouthernNewEnglandandOhioValleyreflectspersistentlydrysurfaceconditions(i.e.,drought)

Above-normalevaporativedemandover2weeksinSouthwest andSouthern Plainscouldsignaldroughtemergence 23

InterpretingEDDIatdifferenttimescalesBycomparingdifferenttimewindows,youcaninferchangesandtrends

2-week(Apr21– May4)

3-month(Feb5– May4)

12-month(May5- May4)

6-month(Nov5– May4)

Eastern ColoradoMost recent 2 weeks have had below-normal evaporative demand (EW1), a change from prior above-normal demand

Overall, early spring had unusually high evaporative demand (ED3 and ED4), strongly indicating drought emergence

Winter and early spring had high evaporative demand overall (ED1-ED4), with higher values for early spring than for winter

The past 12 months saw high evaporative demand overall (mainly ED1), led by the very high values in winter and early spring

24

EDDIcangiveearlywarningofflashdrought—i.e.,rapid-onsetdroughtthatdevelopsinseveralweeks

• InMay-July2012,the2-weekEDDIcapturedseveredroughtconditions intheMidwestup to~2monthsbeforetheUSDroughtMonitor

USDroughtMonitor 2-weekEDDI

25

Moreflash-droughtearlywarning:InMay-July2017intheNorthernPlains,the1-monthEDDIpickedupthedroughtsignalineasternMontana1-4weeksaheadofthe1-monthESI

Figures: Dan McEvoy (EDDI); Chris Hain (ESI)

1-month EDDI 1-monthESI

26

June 4, 2017Evaporative demand normal or low across

region

Keepinmind:NotallareaswithnewEDDI“hotspots”atshorttimewindows(e.g.,2weeks,1month)willseepersistenceofdryconditionsandemergenceofdroughtimpacts,butmanywill—sotheyareworthkeepinganeyeon,especiallyinspringandsummer

1-month EDDI in Four Corners region (UT, CO, AZ, NM)

July 4, 2017Unusually high

evaporative demand in June – which is typically a dry month anyways –

WATCH OUT

August 4, 2017OK - July monsoon rains came in well

above normal; unusually low

evaporative demand 27

Agriculturaldroughtmonitoringwiththe2-weekEDDISummer2015intheWindRiverIndianReservation,north-centralWyoming:EDDIshowsanomalouslyhighE0 fromearlyAugust;agimpactsoccurred

throughout September;USDMfinallyshowssomedrying inlateSeptember

Figure:CandidaDewes,NOAAPSD

IMPACTS IMPACTS IMPACTS

28

Ongoingresearch:PotentialapplicationsofEDDIinwildfireriskmonitoringandhydrologicmonitoringarebeingevaluated

12-m

onth

E0

inJu

ne (m

m)

1000-hour fuel moisture, May-Oct (%)

R 2 = 0.74

E0- fuelmoisturerelationshipacrossS.California• E0 /EDDIshowstrongrelationshipswith

seasonalfuelmoisture(right) andseasonalrunoff (below), despitenotincluding precipitationdirectly

• Researchisongoing toassesstheaddedvalueofEDDIrelativetomoretraditionalindicatorsinthesefields

R 2 = 0.72

SacramentoRiverBasin EDDI vs. Runoff Index(SRI)

Figures:DanMcEvoy 29

Con

tribu

tions

to c

hang

es

in 1

2-w

eek

E0

(mm

)

Sacramento River basin, CA

(Hobbins et al., JHM 2016)

Example:Droughtintensification(increasingE0)wascausedby:

•First,below-normalHumidity

•Then,increasingTemperature and,toalesserdegree,Radiation

•Windspeed playedlittlerole

Ongoingresearch:Splittingevaporativedemand(E0)intoitsfourmeteorologicaldriverscanhelpdiagnosethecausesofthedemandsideofdrought

Evaporative demand (E0)

Temperature

RadiationHumidity Wind speed

Con

tribu

tions

to c

hang

es

in 1

2-w

eek

E0

(mm

)

Sacramento River basin, CA – February - July 2014

Figure:MikeHobbins 30

WheretogetcurrentEDDImaps

USmaps,alltimewindowsfrom1weekto12months:

EDDIhomepagehttps://www.esrl.noaa.gov/psd/eddi/andclickthe“CurrentConditions” tabOrGoogle:EDDIdrought

RegionalmapsinwesternUS,selectedtimewindows:

CCC-NIDISIntermountainWestDroughtBriefinghttp://climate.colostate.edu/~drought/

WWAClimateDashboardshttp://wwa.colorado.edu/climate/dashboard.htmlhttp://wwa.colorado.edu/climate/dashboard2.html

31

WheretogetpastEDDImaps

USmaps,alltimewindowsfrom1weekto12months,from1980topresent.

EDDIhomepage– EDDIMapArchivehttps://www.esrl.noaa.gov/psd/eddi/andclickthe“EDDIMapArchive”tab

32

Wheretogethistoricaltime-seriesofEDDI

OtherEDDIdataneeds?Contactmike.hobbins@noaa.gov ordaniel.mcevoy@dri.edu

EDDIhomepagehttps://www.esrl.noaa.gov/psd/eddi/andclickthe“TimeSeries”tabOrGoogle:EDDIdrought

33

ForfurthertechnicalbackgroundonEDDI,seethispairofpeer-reviewedpapers

Ifyoucan’taccessthesepapersviatheabovelinks,orneedothertechnicalinformationaboutEDDI,contactcontactmike.hobbins@noaa.gov ordaniel.mcevoy@dri.edu

• M.Hobbins, A.Wood,D.McEvoy,J.Huntington, C.Morton,M.Anderson, andC.Hain(June2016):TheEvaporativeDemandDroughtindex:PartI–LinkingDroughtEvolutiontoVariationsinEvaporativeDemand.Journalof Hydrometeorology,17(6),1745-1761, doi:10.1175/JHM-D-15-0121.1

• D.McEvoy,J.Huntington,M.Hobbins, A.Wood, C.Morton,M.Anderson, andC.Hain(June2016)TheEvaporativeDemandDroughtindex:PartII–CONUS-wideAssessmentAgainstCommonDroughtIndicators.Journalof Hydrometeorology,17(6),1763-1779,doi:10.1175/JHM-D-15-0122.1

34

Acknowledgements• TheEDDITeam:JoeBarsugli1,3,CandidaDewes1,4,MikeHobbins1,

JustinHuntington2,JeffLukas3,DanielMcEvoy2,CharlesMorton2,ImtiazRangwala1,3,4,AndreaRay1,3,HeatherYocum1,3

• Fundingandothersupport:

– NationalIntegratedDroughtInformationSystem(NIDIS)– NOAAJointTechnologyTransferInitiative(JTTI)– NOAASectoralApplicationsResearchProgram(SARP)– 1NOAAESRLPhysicalSciencesDivision(PSD)– 2DesertResearchInstitute(DRI)/WesternRegionalClimateCenter

(WRCC)– 3WesternWaterAssessment,CIRES,UniversityofColorado– 4DOINorthCentralClimateScienceCenter

35