Robert Moore and Steven ColeCentre for Ecology & Hydrology, Wallingford, UK

Eric Wood Symposium: Observations and Modeling across ScalesSession 2 Hydrologic and coupled hydroclimate predictions, from real-time to

climate scales, and their applications2 June 2016, Princeton University, USA

Distributed flood forecasting from countrywide to urban and

field scales

● UKSummer2007floods§ £3billion insurancepayouts

§ 55,000propertiesflooded,36,000fromsurfacewaterflooding

§ Nationalinfrastructureimpacts

§ 140,000homeswithoutcleanwater for17days

§ 42,000homeswithoutpowerfor24hours

● UK Government commission Pitt Review§ FloodForecastingCentre& ScottishFloodForecastingService

§ CountrywidefloodforecastingusingG2Gdistributedmodel

Background

Lumpedcatchmentmodel

Distributed Hydrological Modelling (G2G)

― Catchment-widestorm― Lowercatchmentstorm― Uppercatchmentstorm

Grid-to-Grid(G2G)Model

•Onemodelforlargeregion(UK)• Flowestimatesineachgrid(1km2)•Realisticresponsetodifferentstormintensitiesandextent

Gaugingstation

Benefits

Flow

m3 s

-1

G2G

Time(days)

30%increase!

Moore et al., IAHS Publ. 305 (2006); Cole & Moore, JoH (2009)

• Usesspatialdatasetsonterrain,soil/geology,land-cover• Respondstospatialvariationofrainfallinput• UsedoperationallyacrossBritainata1km,15minresolution

Grid-to-Grid (G2G) Distributed ModelSoilmoisture

Riverflow

Moore et al., IAHS Publ. 305 (2006) Price et al.; Cranston & Tavendale, Water Management (2012)

Flood Guidance Statement (FGS)

•G2GforecastsinformFloodGuidanceStatement

•Dailyfloodriskassessmentforemergencyresponders(10:30)

•Updatedduringevents

•Informationpresentedatcountyleveloutto5days

m3s-1Normal2 year flood

More extreme

1km maps

G2G flow outputs converted to flood return periods using

Q(T) maps

G2G for Scotland

Cranston and Tavendale, Proc. ICE – Water Management (2012)

•Recentimprovementinlocalforecastingmodelcoverage

•BUT stilllargeareasofScotlandwithout afloodforecastingcapability

•FloodRiskManagement(Scotland)Act2009

•CreatedjointMetOfficeandSEPAScottishFloodForecastingService

•G2Gappliedtogivefirstnationalpictureoffloodrisk

•Snowmeltmoduleneeded

G2G for Scotland – Snowmelt modellingModel

Performance(R2)

NoSnowmelt

G2G for Scotland – Snowmelt modelling

NoSnowmelt

WithSnowmelt

ModelPerformance

(R2)

Majorimprovementinmodelperformance

G2G for Rapid Response Catchments

Area <100km2All stations

R2 Efficiency

• Explore use of G2G for Rapid Response Catchments• typically small area (<100km2) & ungauged; can be urban• need to develop forecast/warning capability• Value of radar/NWP rainfall forecast ensembles?• Case study experience & methods of display

G2G simulation (Jan – Apr 2008)

• Post-processingschemetogeneratelargerainfallensemblescheaply

• Seamlesscombinationofnowcast anddeterministicNWPforecast

• NoiseusedtogenerateensemblesanddownscaleNWP

• 12members(now24),15minuteaccumulations,7hNowcast every15mins,24hBlendedensembleevery6h

Forecasttimeorigin

Q(T)returnperiodthresholdused

Circlesdenotegaugingstations

Solidoutline:area<50km2

Observedflowexceedsthresholdduring forecast

PercentageofensemblesthatexceededtheQ(T)thresholdatsomepointduringforecast

00-33% 34-66%>67%

Ensemble forecast display: region summary

ThresholdForecastOrigin

Qmed/2Qmed Q(5)Q(50)

Case study: 6-7 July 2012

06-07-201207:15

ThresholdForecastOrigin

Qmed/2Qmed Q(5)Q(50)

Case study: 6-7 July 2012

06-07-201207:15

06-07-201219:15

07-07-201200:15

07-07-201207:15

Earlysignaloffloodrisk“hotspots”

Case study: 6-7 July 2012

YealmatPuslinch(55km2) AxeatChardJunction(85km2)

07-07-201200:15

07-07-201207:15

● Strongsignalatleast12hoursbefore

06-07-201219:15

06-07-201207:15

Commonwealth Games Glasgow Pilot• SurfaceWater(Pluvial) FloodForecastproduct•OperationaltrialtosupportCommonwealthGamesOrganisers• Informationon(i)hazard,(ii)potentialimpactsand(iii)risk

Commonwealth Games Glasgow Pilot

Speight et al.; JFRM (2015) in revision Moore et al., CREW Science Report (2015)

Commonwealth Games Glasgow Pilot

Hazard

Impact&Risk

•Modelgavegoodguidanceforactualheavyrainfallevent

1km 500m

250m 100m

Model resolution: flows at 4 spatial scales

50 km2 catchment Flanders, Belgium15:00 13 Nov 2010

1km 500m

250m 100m

50 km2 catchment Flanders, Belgium!5:00 13 Nov 2010

G2G soil moisture at four spatial scales

100m100m

500m1km

250m

50 km2 catchment Flanders, Belgium

G2G river/land cells at four spatial scalesFlow path: blue lineChannel density: blue shading

Model resolution discussion points● Land/rivercellsdefinedusingdigitisedrivernetworkbutpooralignmentwith5mflowpathatfinestresolution(100&50m)meantdrainedareathreshold(0.5km2)usedtheninstead

● Processdemarcation§ Landcells:turbulentoverlandflow,qs§ Rivercells:channelflow,qc

α

⎟⎠⎞

⎜⎝⎛Δ

Δ= 2xVxCqs

α

⎟⎟⎠

⎞⎜⎜⎝

⎛

Δ=

cccc xw

VCwq

Conveyance, nsC /0= ;Meanlandorchannelslope, 0s

Manningroughnesscoefficientoflandorchannel,n(m-1/3s)

Land-cellorriver-pathlength, xΔ ( cxΔ );Channelwidth, cw

Storedwatervolume,V;Exponent, 3/5=α Scale dependence of n

Model resolution outcomes● 1km2 modeldifficulttobeatatoutletlocation(only500mmarginallybetter).Slightlybetterhydrographmatchingforinternallocationsforfinerresolutions.Suggestsuseofthisresolutioninoperationalsettingunlessinputrainfallbetterresolved.

● Differentspatialsupportateachresolutionmeansoptimalparametersvarywhilstuseoffixedsetleadsto20-30%performanceloss.

● Performancesensitivetochannelroughnessandtolandroughnessatfinestresolutionswhenreturnflowfractionandlateralflowmultiplierbecomeimportant.

● Modelrun-timesincreasesubstantiallyforfinerresolutions(100and50m).

Closing remarks● StepchangeinfloodforecastingcapabilityacrossBritain

§ G2Gprovidesfluvialforecasts“everywhere”ona1kmgrid

§ Probabilisticforecastsoverseveraldays possible

● G2GhasshownutilityforRapidResponseCatchments§ Useshigh-resdeterministicandprobabilisticrainfallproducts

§ Casestudiesshowspotential forearlywarning(possibly12h+)

● Real-timemappingofsurfacewaterfloodingimpacts§ Movefromstatictodynamicmapsofhazardandimpact

§ Presentationofresultskey:local(urban),regionalandnational

● Scaledependenceandmodelresolutionissuesworthinvestigatingforapplicationsneedingfieldscaledetail