Steve TaylorFlood Forecasting Team Leader

Anglian Region

Environment Agency

Historical Context Ministerial Directive in 1996 Easter Floods 1998, Bye Report Boscastle 2004, Carlisle 2005 Summer 2007 floods, Pitt

Report

Flood Forecasting in Anglian Region 300,000 homes & businesses

at risk Forecasting, Detection and

Monitoring carried out centrally Issuing flood warnings,

response and recovery carried out locally

Upstreamoutstation/ raingauge/ radar

Downstreamrisk area

Severe Flood Warningthreshold

Flood Warningthreshold

Severe Flood Warningtrigger

Flood WarningTrigger

Setting Flood Warning Trigger levels

River

Areas define minimum lead time requirede.g. time required for full dissemination/

response

“X” hours

Building/ defence etc.

How long will theflooding last?

How bad will it be?/ Whenwill it start to improve?

When will floodingbegin?

Detection■ Weather radar network

■ New radar planned for East Anglia

■ Provide higher resolution data for East Anglia

© met office

Monitoring - SWANTEL Telemetry

June/ July 2007

370,000 calls to outstations

31,000 alarms generated

Flood Forecasting in Anglian Region Model coverage based on risk Move to less complex, more

“useful” models At least 2 methods for each

location Prefer schedule to ad hoc

Forecasting – AFFS

Forecasting - AFFS

Radar actuals

Raingauge

Observed Forecast

Forecasting - Rainfall Hierarchy

Numerical Weather Prediction

Radar based forecast

The move to Probabilistic Forecasts Warning message links

forecast to response Little used in flood warning

around the world Graphical backed up with text

preferred Requires cultural shift by users

Extreme Rainfall Alert Service Pilot Forecast for low probability

high impact rainfall events 6 month free trial from July

2008 Open to Cat 1 & 2 responders Up to 24 hours in advance of

rainfall

Extreme Rainfall Alert Service Pilot

Probabilistic Rainfall Forecasts

Probabilistic Wind Forecasts

Probabilistic Surge Forecasts

Probabilistic Flood Forecasting

Probabilistic Flood Forecasting

Probabilistic Flood Forecasting

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Flo

w (

m3 /s

)

Minor flooding

Moderate flooding

Major flooding

Deterministic Flood Warnings

25 mm in 3 hours

15 mm in 3 hours

Probabilistic Flood Warnings

30% Probability ofthreshold exceedance

70% Probability ofthreshold exceedance

60% probability of > 20 mm/hr

20% probability of > 20 mm/hr

40% probability of > 20 mm/hr

Probabilistic Flood Warning

Probability of a “Severe Flood Warning”

9% 30% 55% 85% 47%

Day 1 Day 2 Day 3 Day 4 Day 5

Probabilistic Flood Warning

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 2 3 4 5

Date

Prob

abili

ty

Severe flood warning Flood warning Flood watch All clear

Probabilistic Flood Warning

Summary Forecasts are never ‘right’ Shift to probabilistic forecasts Desire to forecast surface

water flooding Future decisions made

according to risk