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Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland
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Ensemble rainfall predictions in a countrywide flood forecasting model in Scotland

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  • 1. Using ensemble rainfall predictions in acountrywide flood forecasting model inScotlandMichael Cranston, EGU General Assembly 2012Why Predict? The value of prediction inhydrological sciences and policy © Crown copyright
  • 2. Acknowledgements • Bob Moore, Steve Cole, Alice Robson, Vicky Bell and Phil Howard of CEH Wallingford • Alex Minett and Marcel Ververs of Deltares • Peter Buchanan and Alan Motion of Met Office • Richard Maxey, Amy Tavendale, Lauren McLean and Rachel Geldart of the Flood Forecasting and Warning Section of SEPA© Crown copyright
  • 3. Aims • What policy is driving our flood forecasting developments • What are the key challenges in flood forecasting uncertainty and how are we tackling this through science developments and applications • What have we learned from recent operational experience of use of probabilistic flood forecasts© Crown copyright
  • 4. Flood Risk Management (Scotland) Act 2009 Science to improve flood forecasting Flood warning and risk based communication© Crown copyright
  • 5. Flood Warning Policy “…SEPA will aim to reduce the impact of flooding through the provision of actively disseminated, reliable and timely flood warnings to registered users of a national flood warning service. …and SEPA will aim to provide an effective flood warning service and to reduce the impact of flooding from all sources.”SEPA (2010) Statement of Intent for Implementing Flood Warning Duties under the Flood Risk Management Scotland Act© Crown copyright
  • 6. Service Expectations “…public expectations around flood warning systems can never be fully met.”Association of Chief Police Officers (2008) Scottish Parliament Flooding and Flood Management Review, RAE Committee 2nd Report.© Crown copyright
  • 7. Hydro-meteorological forecasting “…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 floods.”Scottish Government (2008) Scottish Parliament Flooding and Flood Management Review, RAE Committee 2nd Report.© Crown copyright
  • 8. National guidance on expected flood risk based on risk based approach (likelihood and impact). Raising vigilance and awareness. Lead time T +5 days Administrative authority level scale alerts when flooding is possible – be prepared. Lead time T +24 – 36 hours Community level warning when flooding is expected – Immediate Action Required. Lead time T+ 3-6 hours© Crown copyright
  • 9. Flood forecasting on a national scale – Is this achievable?© Crown copyright
  • 10. Distributed Model Structure Grid-to-Grid (G2G) Distributed Model Precipitation Evaporation Surface flow-routing Saturation-excess River Runoff- surface runoff producing soil column River flow Return Drainage flow Subsurface flow-routing • Uses spatial datasets on terrain, soil/geology, land-cover • Responds to spatial variation of rainfall inputAcknowledgement: Moore et. al, CEH Wallingford, 2011
  • 11. G2G Model: runoff shaping Factors shaping runoff production in G2G Urban/Suburban coverage Soil properties •Increase runoff (by (for each HOST class) decreasing soil depth) G2G Runoff Production Soil Moisture Deficit (modelled) Gridded rainfall Terrain/slope Steep slopes → Shallow storage Shallow slopes → Deep storageAcknowledgement: Moore et. al, CEH Wallingford, 2011
  • 12. G2G Model Performance: R2 Efficiency 2008 Water Year (all configured sites)Acknowledgement: Moore et. al, CEH Wallingford, 2011
  • 13. Quantitative Precipitation Forecasts • Deterministic Grid-to-Grid utilises best available (greatest resolution) weather prediction • Nowcast (2 km) • UK4 (4 km) • North Atlantic European (12 km) • Global (25 km) • Ensemble Grid-to-Grid utilises current operational MOGREPS-R (18 km)© Crown copyright
  • 14. P > 25% P > 75% MOGREPS members T +54 UKPP, UK4, NAE, GM deterministic T +144Flood Forecasting and Warning
  • 15. Operational Utility4th January 2012• Countrywide assessmentof flood risk• Probability of exceedingflow threshold Q(T)• Good indication offlooding hotspots© Crown copyright
  • 16. © Crown copyright
  • 17. © Crown copyright
  • 18. Flood Peak Flow Warning G2G G2G G2G Warning Status Deterministic MOGREPS % ileThreshold (Q) Peak Median FW (Q) (Q) (Q) Crossing 105 395 205 118 75% 112 321 281 224 100% 70 66 59 62 25% 126 110 93 116 25%
  • 19. © Crown copyright
  • 20. Value of countrywide forecasting • Distributed model provides spatial representation of forecast risk with lead time of 1-2 days, especially when using probabilities • Greater accuracy of river flow forecast when using higher resolution deterministic QPF models • Ensemble-based MOGREPS-R forecasts provide objective assessment of risk on a national scale© Crown copyright
  • 21. National guidance on expected flood risk based on risk based approach (likelihood and impact). Raising vigilance and awareness. Lead time T +5 days Administrative authority level scale alerts when flooding is possible – be prepared. Lead time T +24 – 36 hours Community level warning when flooding is expected – Immediate Action Required. Lead time T+ 3-6 hours© Crown copyright
  • 22. Application for flood warning “…(the forecast) provided a useful heads up, not only for the potential for high levels especially within the Irvine but also the confidence that could be attributed to these forecasts by seeing the spread of the predicted hydrographs. …it did mean that … I was more prepared.”David Fadipe (2012) Flood Warning Duty Officer response to consultation on use of probabilistic forecasts, pers. comms.© Crown copyright
  • 23. Conclusions • Greater than ever expectations on flood warning delivery based on policy drivers • Significant advances in hydrometeorology with specialists working together • Use of ensemble prediction good at countrywide scale but higher resolution (storm scale) models needed for flood warning application • Understanding uncertainties helps risk based flooding guidance and communication© Crown copyright

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