ImprovethephysicsofthetreatmentofET(andhenceevapora4vedemand)

inCBRFCopera4ons,andtherebyimprovewatersupplyforecastskill.

ET = actual evapotranspiration

CooperatewithNWSWesternRegionScien4ficServicesDivisioninprovision

ofscien4ficallysound,distributedET‐relatedforecaststoend‐users.

CBRFCEvapotranspira4onstudy

HowETiscurrentlyes4matedbytheNWSRiverForecastSystem

Sacramento‐SoilMoistureAccoun4ng(Sac‐SMA)modelevaporatessoil

moisturefromtwodepths.

EpdrivenbyEpanclimatology:• e.g.,Jan1,1979=Jan31,1979=Jan31,2010• seasonaldatadisaggregatedtodaily,• missingseasonsfilledin,

• adjustmentfactorPEADJcalibratedtowaterbalance.

WeWeryearsinsouthernCBRFCregion(e.g.,SanJuan),orwhen/wherePrcp

drivesRunoff,weunder‐forecastRunoff,orover‐es4mateET.

Op4ontouse4me‐seriesinSac‐SMA,downtosix‐hourly:• bestop4onistouseobservedEp,

•  cannotuseEpanatadailyorsub‐dailyscale,

• bestmodelingop4onisaPenman‐basedes4mate,•  heavyondatainputs/parameters.

Ep = evaporative demand Epan = pan evaporation

Prcp = precipitation

• synthe4cmeasureofevapora4vedemandtosynthesizeEpanobserva4ons.

• mixtureofradia4on(sunshineandIR)anddryingpoweroftheair(humidityandwind).

• accountsforinstrumenta4oneffects:o extrasunshineintercep4onbypanwalls,o increasedturbulenceacrosswatersurface.

Physicallybasedmodels:PenPanEpan(synthe4cpanevapora4on)

EpanforApril25,2010(mm)

Qn = energy available for ET U2 = wind speed

esat-ea = vapor pressure deficit (~ humidity) IR = infra-red, or long-wave radiation

Preliminaryresults:climatologyofdynamicdailyEpan,Ep,andETrc–TenmileCreek,CO

Ep=0.7*Epan

Preliminaryresults:dynamicEpanvs.historicsimulatedstreamflowerrors

Preliminaryresults:dynamicEpanvs.historicsimulatedstreamflowerrors

Concept:• dailysimulatedstreamflowerrorsaregeneratedfromSac‐SMA/SNOW‐17modelinRFCopera4ons,runningsta4cEp(i.e.,climatologicmonthly),

• errorsarecomparedtodynamicEpanfroma30‐year4me‐series.

Results:•  greateststreamflowerrors(+/‐)occurwithhighestEpanatall4me‐scalesto3‐monthly,

•  rela4onislessclearathigher4me‐scales(monsoonandwatersupplyseasons,annual),

• highestcorrela4onbetweenmonthlyerrorandmonthlyEpanisMarch/April.

Caveat:• thisisonebasin:

• TenmileCreeknearBreckenridge,CO• high‐eleva4onheadwaterbasin,• snowmelt‐dominated.

• adjusts Penman Ep to model seasonality in vapor transfer process through aKP and bKP:

• seasonal functions of day of year,

• calibrated in Kimberly, ID,

• uses regularly forecast meteorological data.

• here, ETrc is a specific case of ET calculated for specific biological and physical conditions (a hypothetical reference crop):

• well-watered alfalfa/grass of height 0.12 m, rs = 70 sec/m, α = 0.23, rs = 208 sec/m,

•  uses regularly forecast meteorological data,

•  international standard (FAO-56).

• very commonly used in agricultural community.

Forecas4ngETrcacrossNWSWesternRegion:

Penman‐MonteithETrc

ETrcforecastforMay3,2010(mm)

KimberlyPenmanETrc 

CBRF

C&

WR‐SSD

WFO

PR

ODUCT

ETrcforecastgrid

• 2.5‐kmresolu4on• daily/weeklyoutlook

ETrcpointforecast

• value‐added•  sta4s4calcontext

•  spa4alcontext

ETrcclimatologygrids• NLDAS‐derived•  0.125oresolu4on• CONUS‐wide• daily/weekly• movingwindow/sta4cweeks

meanvarianceminimum90%exceedancemedian(50%)10%exceedancemaximum

GFEscript

e.g.,hWp://www.wrh.noaa.gov/sto/et

WFO

FO

RECA

ST

+ + +Inputforecastgrids

• NDFD‐derived• 2.5‐kmresolu4on• hourly

Wind Temperature Dewpoint Skycover

Forecas4ngETrcacrossNWSWesternRegion:deliveryconcept