“the warnings work according to the river ... - hydrology · x. deterministic forecast. analysis....

“The warnings work according to the river levels whereas actually weought to maybe be giving people warning when we’re expecting excessiverainfall”

David Cameron, 19th November 2010 (BBC Cornwall website)

Structure

The contextKey challengesThe future

Reproduced by permission of Ordnance Survey on behalf of HMSO. © Crown copyright and database right 2010. All rights reserved. Ordnance Survey Licence number 100026380. © Environment Agency.

Bruton 1917

Cannington 1924

Lynmouth 1952

Martinstown 1955

Chew Valley 1968

Chulmleigh 1982Polperro 1993

Boscastle 2004

Ottery St Mary 2008

St Ives 2009

Reproduced by permission of Ordnance Survey on behalf of HMSO. © Crown copyright and database right 2010. All rights reserved. Ordnance Survey Licence number 100026380. © Environment Agency.

Tanhouse Stream, Lostwithiel (Uzella)

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18:1518:4519:1519

:4520:1

520:4521:1521:4522

:1522:4

523:1

523:4500:1500

:4501:1

501:4

502:1502:4503

:1503:4

504:1

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:4506:1

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507:1507:4508

:1508:4

509:1

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:4511:1

511:4

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:1513:4

514:1

5

Time (16/17th Nov)

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nfal

l (m

m)

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luxulyan rain Tanhouse Stream

Mevagissey (Fire Station Screen)

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507:1

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510

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:4512:1512:4

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Time (16/17th Nov)

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nfal

l (m

m)

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(m)

Helligan mg fire stn u/s

Images: bbc website, Adam Gerrard SWNS.com

Key Challenges

Rainfall Rainfall Runoff modelsCoverage

Image: Adam Gerrard SWNS.com

Radar Radar actualsactuals

RaingaugeRaingauge

Observed Forecast

Numerical Weather PredictionNumerical Weather Prediction

Radar based forecastRadar based forecast

Precipitation Hierarchy

Event rainfall totals

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Helligan Luxulyan Bodmin Bastreet St Clether

Location

Rain

(mm

)

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% D

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ence

Rain gauge Radar Observed Difference

Maximum Hourly intensities

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Helligan Luxulyan Bodmin Bastreet St Clether

Location

Rain

(mm

/hr)

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ence

Rain Guage Radar Observed Difference

6:19 am Predannack 45 degrees azimuth

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500 50 100 150 200 250 300 350 400

Range (bin)

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n ra

te (m

m/h

)

Uncorrected RCorrected R

River Neet – Woolstone Mill

Woolstone Mill observed radar and TBR cumulative catchmnet rainfall 17-11-2010

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GMT

Time (hh:mm)

Rai

nfal

l (m

m)

Observed TBRCumulative TotalObserved RadarCumulative Total

River Neet – Woolstone Mill

time Forecast uncertainty

Climatology

Initial Condition Uncertainty

X

Deterministic Forecast

Analysis

Ensembles

Extreme Rainfall Alert – 16 Nov 16:22hrs

Confidence in rainfall runoff models with extreme and localised rainfall

Confidence in rainfall runoff models with extreme and localised rainfall

Confidence in rainfall runoff models with extreme and localised rainfall

Confidence in rainfall runoff models with extreme and localised rainfall

Ottery St Mary 2008

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0.5

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2.5

16/11

/2010

21:00

16/11

/2010

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/2010

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/2010

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/2010

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/2010

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/2010

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/2010

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18/11

/2010

09:00

Stag

e (m

)

Observed Stage

Simulated stage usingthe old ratingSimulated stage usingthe new rating

Image: BBC website

Summary

Errors in deterministic rainfall forecastTargeting probabilistic rainfall forecastsRain gauge densityAssumptions of modelling approachesCoverage of good quality hydrometric dataCulverts and trash screens

The Future…

Image: AP