Michael CranstonFlood Forecasting and Warning Manager

SIPR Event, Dundee, 21st June 2011

Forecasting and Warning – meeting the needs of partners

How do emergency plans best adapt to new advance forecasting…

Aims

• Review the developments in flood forecasting and warning

• Consider the challenges for

• The science

• Communication of flooding risk

Part 1: Review the Developments in Flood Forecasting and Warning

Developments in Flood Forecasting and Warning

“…public expectations around flood warning systems can never be fully met.” Association of Chief Police Officers of Scotland.

Scottish Parliament (2008) Flooding and Flood Management Review, RAE Committee 2nd Report

Recommendations for Flood Warning

• National flood warning strategy and further expansion including coastal areas

• Direct dissemination of warnings

• Pluvial flood warnings

• Developing the science to improve flood warnings

• Understanding the risk – critical infrastructure

• Improving public access and understanding

Direct Dissemination of Warnings

• New direct warning service through Floodline

• Launched March 2011

• 220 flood warning areas

• Now has over 10,000 customers

• 20% of those targeted to receive warnings

Direct Dissemination of Warnings

Developing the Science

“…Evidence suggests that increased lead times for predicting events are directly related to reductions in the damage caused to properties and infrastructure.”

Pitt (2008) Lessons learned from the 2007 summer floods.

Developing the Science

Developing the Science

• Development of SEPA’s flood forecasting capabilities

• Launch of FEWS Scotland in 2007

• State of the art flood forecasting technology

• Incorporating hydrology and meteorology data to provide flood forecasts for selected catchments

• Data and forecasting openly shared with responders

Developing the Science

“…The regular updates received from SEPA – re. the river levels and the Met Office – re. the weather forecast helped to determine decisions regarding the allocating of resources by all services involved..” East Ayrshire Council

Hydrological and Meteorological Collaboration

“…the committee recommends that the Scottish Government ensures that SEPA has the necessary funding to enable it to collaborate with the Met Office to provide an effective flood warning system for all types of flooding.”

Scottish Parliament (2008) Flooding and Flood Management Review, RAE Committee 2nd Report

Service Aims

• Provide a joint hydrological and meteorological forecasting service to promote flood vigilance 5 days ahead

• Provide a joint service to provide surface water/flash flooding alert service in the future

• Provide better forecasting support service to SEPA’s regional flood warning teams

SEPA

Area Flood Warning Teams:•Flood Detection (local)•Flood Forecasting (local)•Flood Warning

Real time dataFEWS

Met Office

Services to Government:•Forecasts•Heavy Rainfall Warnings•Radar/forecast output

Public Weather Service:•Forecasts•NSWWS•PWS Advisors

CCA Responders – Flood Response

Flood ForecastingCentre

NSWWS:AlertWarning

Flood Warning

Forecasts and Alerts under contract

Flood Forecasting Service

•Flood Vigilance•Flood Forecasting (strategic)•Flood Detection (strategic)•Flood Advice•R&D

UKCMFR&DConsistency of productsX-border coordination

Flood Guidance

Highlights

• Providing a new flood guidance product to 150+ customers in Scotland

• Improved countrywide communication on flood risk

• More targeted meteorological guidance and forecast for flood warning

• Improved flood awareness and vigilance, particularly for new customers

Part 2: The Challenges Ahead

Surface Water Flood Risk

“…the committee is particularly struck by the absence of any pluvial warning system…(but) does not underestimate the technical and practical challenges...”

Scottish Parliament (2008) Flooding and Flood Management Review, RAE Committee 2nd Report

Challenges Ahead

• Developing our forecasting capabilities and science

• Communication of flood risk

Building our forecasting expertise

• Partial coverage of hydrological modelling capabilities

• Challenges in observations and forecast of rainfall

• Combined implications for providing countrywide flood forecasts

• Rapid response catchments and surface water flooding

Grid to Grid Countrywide Forecasts

CEH Wallingford (2009) Provisional application of the G2G Model to the Irvine events of October 2009. CEH Wallingford, Wallingford, Oxon., 8pp.

The value of nowcasts in hydrological forecasting

“…it is demonstrated that the rainfall predictions provided by Nimrod (UKPP) are uncertain and at times biased, it is also shown that there is considerable benefit in their use for flood forecasting when compared to the alternative of using no future prediction of rainfall.”

Werner and Cranston (2009) Understanding the value of radar rainfall nowcasts in flood forecasting and warning in flashy catchments. Meteorol. Appl., 16, 41-55.

Semi-permanent bands of rain in SE flow (believed to be ‘orographic correction’), Good example along Great Glen (this can bleed through to ‘nowcast’ and associated products) and lead to unrealistic accumulations.

Managing uncertainty and error

Uncertainty in Forecasts

• How are the errors in radar measurement propagated into rainfall forecasts

• What more can hydrologists do to manage this uncertainty

• What additional challenges are there to going beyond 6 hours in flood forecasting

STEPS Nowcasts (T+6)

- Locally intense rainfall over the 6 hour model period

- Confirmed previous 36 and 24 hour predictions

- Over 100 mm recorded in Tyndrum

Deterministic UK4 Model

- 24 hour forecast accumulation up to 1800 on Wed 6th April 2011

- Forecast for approx 24 hours of rain, often heavy with significant accumulations.

- > 100 forecast

MOGREPS-R

- Well defined area of >50MM in 24 HR up to 1800 on 6th April.

Probability high and fits with area of high risk and deterministic forecasts hence reasonably high confidence.

Uncertainty in Forecasts

Raingauge

Radar

T0

Automatic Input to Hydrological Model

STEPS T+6

UK4 T+36

MOGREPS-R T+54 >

Challenges in communicating uncertainty

“…if someone had told us that these estimates (flood forecasts) were not an exact science, or that other countries predict potential river crest heights in probabilities for various levels, we may have been better prepared.”

Glassheim (1997) Fear and loathing in North Dakota. Natural Hazards Observer, XXI, 1-4.

Challenges in communicating uncertainty• Need to clear understanding across all

organisations on the risk matrix

Consistency in GuidanceFLOOD RISK MATRIX GUIDANCE

Very Low Low Medium High

Typical Impacts Minimal DisruptionGenerally no impact, however there may be:Isolated and minor flooding of low-lying land and roadsIsolated instances of spray/wave overtopping in coastal roads and promenades

Minor DisruptionLocalised flooding of land and roads – risk of aquaplaningLocalised flooding affecting individual propertiesLocalised disruption to key sites on floodplainsIndividual properties in coastal locations affected by spray and/or wave overtoppingLocal disruption to travel

Moderate DisruptionFlooding affecting parts of communitiesDamage of buildings/structures is possiblePossible danger to life due to fast flowing/deep water/ wave overtopping/ wave inundationDisruption to infrastructure

Significant DisruptionWidespread flooding affecting whole communities Collapse of buildings/structures is possibleDanger to life due to fast flowing/ deep water/ wave overtopping/ wave inundationWidespread disruption or loss of infrastructureLarge scale evacuation of properties may be required

Expected Partner Response Level

Business as usual Single agency operational response.

Multi-agency response likely to be needed Predominantly at tactical level. SGoRR may be considered

Multi-agency strategic response likely at SCG level or regional level. Mutual aid likely with perhaps national co-ordination. SGoRR convened.

Implications for public

Generally no impact; however there may be some isolated and minor flooding. Little or no disruption to travel although wet road surfaces could lead to difficult driving conditions.

Localised flooding possible. Wet road surfaces and possibility of ponding water, especially in known trouble spots. Local disruption to travel – longer journey times.

Flooding of land and roads and property is likely. Disruption to travel and infrastructure

Widespread flooding of property. Severe disruption to travel. Loss of gas, electricity, water supplies. Significant disruption to communities.

Guidance on likelihood

Confidence is very low. Forecast suggests less than 20% chance of occurrence.

Confidence is very low. Forecast suggests between 20% and 40% chance of occurrence.

Confidence is medium. Forecast suggests between 40% and 60% chance of occurrence.

Confidence is medium. Forecast suggests greater than 60% chance of occurrence.

Challenges Ahead

• Development of countrywide flood forecasting system – forecasts ‘everywhere’ out to 5 days

• Needs very close meteorology and hydrology working to understand the uncertainties and predict shorter lead time flooding

• Need for clear communication of flood risk for all sources of flooding

Conclusions

• Significant effort into developing forecasting and warning

• Combined hydrological and meteorological understanding of the flood risk from all sources

• …but not without considerable challenges

Forecast 21st June 2011

There is a low risk of flooding in eastern Scotland through today and into Wednesday which may lead to minor disruption. For the remainder of the forecast period and areas, flooding risk is very low.

Flood Guidance Statement (21st June 2011) Scottish Flood Forecasting Service

Forecast 21st June 2011

Forecast 21st June 2011

Forecast 21st June 2011

Forecast 21st June 2011