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
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
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
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
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
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