1. Steve Taylor Flood Forecasting Team Leader Anglian Region
Environment Agency

2. Historical Context Ministerial Directive in 1996
Easter Floods 1998, Bye Report
Boscastle 2004, Carlisle 2005
Summer 2007 floods, Pitt Report
Quick run through the main political drivers that result in the current look of the flood forecasting service. Reference to Pitt to highlight the key outcomes for flood forecasting being recommended by Pitt.
s.166 of the Water Resources Act 1991 gives the Agency specific powers to carry out works for the purposes of providing a flood warning system. In March 1996, the Secretary of State gave direction that the NRA would become the lead agency in disseminating warnings of the danger of flooding.
Pitt rec 1 – monitoring g/water levels
Pitt rec 2 - id areas at high risk of SW flooding
Pitt IC 3 - develop forecasting tools
Pitt IC 7 – assess possibility of forecasting where SW flooding will occur
Pitt IC37 – EA/ MO assess options for issuing warnings for lower probablility events.

3. 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
Brief run through the at risk population, tidal fluvial split and how the overall service is delivered.

4. Setting Flood Warning Trigger levels
How bad will it be?/ When
will it start to improve?
When will flooding
begin?
How long will the
flooding last?
Severe Flood Warning
trigger
Flood Warning
Trigger
Explain how the workload is split between the Warning and forecasting teams. Explain the move from Action Thresholds to Result Thresholds.
Severe Flood Warning
threshold
Building/
defence etc.
Flood Warning
threshold
River
Upstream
outstation/ raingauge/ radar
Downstream
risk area
“X” hours
Areas define minimum lead time required
e.g. time required for full dissemination/ response

5. Detection Weather radar network New radar planned for East Anglia
Provide higher resolution data for East Anglia
Highlight that in the absence of the Anglian radar quality of radar data is not reliable for use in flood forecasting
© met office

6. Monitoring - SWANTEL Telemetry
June/ July 2007
370,000 calls to outstations
31,000 alarms generated
Monitoring undertaken using the Swantel telemetry system. Approximately 900 outstations, 15,000 potential alarms to be managed. Highlight Summer 2007 figures

7. 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
Highlight that coverage is not total and focussed on areas with greatest impact. All locations must have contingency arrangements.

8. Forecasting – AFFS
National forecasting shell used within Anglian. Will host any model type as long as an adapter is developed for new model types. Consists of operator client and customer webservice for viewing results

9. Forecasting - AFFS
Forecasts potentially making use of radar forecasts out to 36 hours. Data quality not sufficient and lead times allow use of shorter lead time but higher quality radar data may be available in the near future if a new weather radar is built at Old Buckenham.

10. Forecasting - Rainfall Hierarchy
Observed
Forecast
Raingauge
Forecasting models will start from the rainfall input. This will be derived from a variety of sources to generate an input sequence. Inherent uncertainty in each input. Is the forecasting model poor or has the rainfall input been inadequate?
Radar actuals
Radar based forecast
Numerical Weather Prediction

11. 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
Uncertainty has to be dealt with. Deterministic forecasts do not represent this uncertainty

12. 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
Advisory issued at 1400 local time for the 24 hours from midnight. Early Alert issued 8-11 hours in advance and Imminent Alert issued 1 – 3 hours in advance. Available via , fax, sms and voic .

13. Extreme Rainfall Alert Service Pilot
Greater than 10% probability of an extreme event occurring across a large geographical area. 30mm per hour, 40mm in 3 hours, 50mm in 6 hours.

14. Probabilistic Rainfall Forecasts
Met Office increasingly making available ensemble forecasts. Environment Agency trialling how these forecasts could be used

15. Probabilistic Wind Forecasts
Wind speed probabilistic forecasts used during major operation engineering works near Ipswich.

16. Probabilistic Surge Forecasts
Surge ensembles give feel for uncertainty. Even large scatter only matters if warning thresholds are crossed. i.e. range could be a metre but only matters if the next highest threshold is crossed.

17. Probabilistic Flood Forecasting
Each solution is equally valid, so which one is “right”?

18. Probabilistic Flood Forecasting
Graphically represent “most likely” range.

19. Probabilistic Flood Forecasting
Major flooding
Start to map uncertainty to impact
Moderate flooding
Minor flooding

20. Deterministic Flood Warnings
25 mm in 3 hours
15 mm in 3 hours
Very definite with deterministic system. Reduced lead time.

21. Probabilistic Flood Warnings
60% probability of
> 20 mm/hr
20% probability of > 20 mm/hr
40% probability of > 20 mm/hr
Greater lead time but increased uncertainty
30% Probability of
threshold exceedance
70% Probability of
threshold exceedance

22. Probabilistic Flood Warning
Probability of a “Severe Flood Warning”
Place greater emphasis of decision making on to local responders and public 9%
30%
55%
85%
47%
Day 1
Day 2
Day 3
Day 4
Day 5

23. Probabilistic Flood Warning
Information can be displayed in a whole range of ways

24. Probabilistic Flood Warning
Updated map based forecasts preferred but potentially technically most difficult

25. Summary Forecasts are never ‘right’ Shift to probabilistic forecasts
Desire to forecast surface water flooding
Future decisions made according to risk