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© Crown copyright 2004 Page 1 Development of a stochastic precipitation nowcast scheme for flood forecasting and warning Clive Pierce 1 , Alan Seed 2 , Neill Bowler 3 1. Met Office, Joint Centre for Hydro-Meteorological Research, Wallingford, Oxfordshire, UK, OX10 8BB 2. Cooperative Research Centre for Catchment Hydrology, Bureau of Meteorology, Melbourne, Australia 3. Met Office, FitzRoy Road, Exeter, Devon, UK, EX1 3PB

Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Development of a stochastic precipitation nowcast scheme for flood forecasting and warning. Clive Pierce 1 , Alan Seed 2 , Neill Bowler 3 1. Met Office, Joint Centre for Hydro-Meteorological Research, Wallingford, Oxfordshire, UK, OX10 8BB - PowerPoint PPT Presentation

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Page 1: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

© Crown copyright 2004 Page 1

Development of a stochastic precipitation nowcast scheme for

flood forecasting and warningClive Pierce1 , Alan Seed2 , Neill Bowler3

1. Met Office, Joint Centre for Hydro-Meteorological Research, Wallingford, Oxfordshire, UK, OX10 8BB

2. Cooperative Research Centre for Catchment Hydrology, Bureau of Meteorology, Melbourne, Australia

3. Met Office, FitzRoy Road, Exeter, Devon, UK, EX1 3PB

Page 2: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Overview

A stochastic QPN scheme - STEPS Overview of the Short Term Ensemble Prediction System Cascade modelling framework STEPS cascade model Uncertainties in advection & Lagrangian temporal evolution Formulation of STEPS

Towards stochastic fluvial forecasting

Propagating uncertainty in QPNs through a rainfall-run-off model Plans

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Short Term Ensemble Prediction System

Model design Cascade framework (Lovejoy et al., 1996; Seed, 2003) to model dynamic scaling behaviour merging extrapolation nowcasts with NWP forecast

Sources of uncertainty / error diagnosed velocity fields (Bowler et al., 2004) Lagrangian temporal evolution NWP forecast initial state

Forecast evolution blends extrapolation, NWP and noise cascades stochastic noise

replaces extrapolated features beyond their life times introduces features unresolved by NWP

ensemble produced

Page 4: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Radar based precipitation field 2-D FFT

Bandpass filter per pixel, k=1,8

Inverse transform

Additive cascade

Normalise Xk(t)

Based upon S-PROG cascade - Seed (2003)

STEPS cascade model

njik

n

kji LLjLitXtdBR 2,,..,1,,..,1),()( ,,

1,

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kkk LL

)(

)()()(

,,

,,,, t

ttXtY

jik

kjikjik

Page 5: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Cascade decomposition

256-128 km

128-64 km

64-32 km

32-16 km 16-8 km 4-2 km8-4 km

courtesy of Alan Seed, Bureau of Meteorology, Australia

Page 6: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Uncertainty in the extrapolation nowcast

Uncertainty in field evolution Modelled in Lagrangian reference frame

Noise replaces extrapolated features beyond predicted life time

k,i,j = temporally independent noise cascade

Uncertainty in advection velocities Add perturbation to velocities

)(60

1)()( lonperturbatil

smoothlnoisy ttvvsmoothft

tvttv

)()()( tvtfttv onperturbatillonperturbati

)()()2()()()()(ˆ,,0,2,1, ,,,,,, ljikkl

nkl

nkl

n ttttttYttttYtttYjikjikjik

analysisn PP

)2()()()()(ˆ,,2,,,1,,, tttYttttYtttY l

ejikkl

ejikkl

ejik

Page 7: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Formulation of STEPS

A blend of three cascades Extrapolation

Noise

NWP

Weights assigned according to skill of extrapolation and NWP components

Advection velocities blend perturbed velocity, e with NWP diagnosed velocity, m

)()(1)()()( 22 lmle

lele

l ttvttwttvttwttv

)( lek ttY

)( lnk ttY

)( lmk ttY

)()()()()()()(,,,,,,,, ln

lnkl

ml

mkl

el

ekljik ttYttwttYttwttYttwttY

jikjikjik

Page 8: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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STEPS - products

Ensemble members - T+15 minutes

Page 9: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Probability of precipitation

STEPS - products

Page 10: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

© Crown copyright 2004 Page 10

Towards stochastic fluvial flood forecasting and warning

Uncertainty in rainfall input dominates (Moore, 2002)

Ignore errors in rainfall-runoff model

PDF of river flow from PDF of rain accumulation

Underestimates total uncertainty (Krzyztofowicz, 2001) Cost-loss decision making model (Mylne, 2002)

Page 11: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Flow forecast ensembles

courtesy of Bob Moore, Centre for Ecology and Hydrology, UK

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Plans

STEPS operational trial in the UK and Australia

starts autumn 2005 pdfs of rain accumulation and river flow (PDM – Moore, 1985)

cost-loss model (Mylne, 2002) for pluvial & fluvial flood warning

verification of deterministic and probabilistic forecasts

Page 13: Development of a stochastic precipitation nowcast scheme for flood forecasting and warning

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Thank you