Flash floods: Current practice and new developments in quantitative precipitation forecasting

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Flash floods: Current practice and new developments in quantitative precipitation forecasting

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Flash floods: Current practice and new developments in quantitative precipitation forecasting

  1. 1. Flash floods: Current practice and new developments in quantitative precipitation forecasting Bruno Rudolf Deutscher Wetterdienst Dpt. of Hydrometeorology DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 1
  2. 2. Overview 1. DWD operational NWP system today 2. Limits of quantiative precipitation forecast 3. Three case studies (meteorol. flood conditions) 4. Ensemble prediction systems, future models 5. Services and summary DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 2
  3. 3. DWD operational NWP system Three nested models: global, Europe, Germany COSMO-DE: x = 2.8 km, 21 hours 8 runs per day COSMO-EU: x = 7 km, 78 hours 4 runs per day GME: x = 30 km, 7 days 2 runs per day DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 3
  4. 4. Limits of predictability Sources of the limits:  chaotic features of the atmospheric circulation  non-steady behaviour of important processes (e.g. condensation, convection and turbulence)  initial meteorological conditions are partly unknown  boundary conditions are partly unknown  the model equations are non linear on a high grade  limits of computer capacity  insuffient spatial resolution DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 4
  5. 5. Limits of predictability Convective cloud dynamics are not sufficiently simulated by the operational NWP models Internal structure and dynamic processes of a convective cloud system DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 5
  6. 6. Case 1: Elbe flood August 2002 GME LM Observations Total of 3 daily forecasts (11, 12, 13 Aug.) The large scale patterns of the precipitation totals were well predicted. • However, the high precipitation totals were considerably underestimated. DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 6
  7. 7. Case 2: Switzerland, Bavaria August 2005 GME LME LM Observations 24h-precip 22 to 23 August , 6:00h (model run: 22 Aug, 00 UTC) The spatial structure of daily precipitation was well predicted. • However, the spatial-temporal sequence was not yet met suffiently. DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 7
  8. 8. Case 3: Local flash flood 2005 ‘Millennium‘ precipitation 14:50 to 17:20 CEST RADOLAN event in Dortmund, Combination of 26 July 2008 Dortmund: radar-based and 200 mm in 2,5 h raingauge-based precipitation The probability catching observations extreme local rainfall by a raingauge is less than 10% even in a dense national network. DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 8
  9. 9. Case 3: Local flash flood 2005 RADOLAN COSMO-EU (7 km) COSMO-DE (2,8 km) Combination of radar model forecasts of 24 hours precipitation and gauge observation DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 9
  10. 10. Ensemble predictions Method: parallel numerical simulation of the same case with modified initial or boundary conditions or parametrisations within a given error range Ensemble predictions deliver: • Probalistic forecasts • Quantification of uncertainties • Risk information DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 10
  11. 11. Ensemble predictions COSMO-DE-EPS ensemble with 20 members for Case 3 - Dortmund 26. July 2008 hourly precipitation totals 15:00 -16:00 UTC COSMO-DE-EPS is still in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 11
  12. 12. Ensemble predictions COSMO LEPS basis ECMWF-EPS Case 2: Flood in Switzerland, Bavaria August 2005 Probability of exceeding the thresholds 50 mm precipitation Probability of 24h- precipitation > 50 mm DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 12
  13. 13. The future forecast models ICON ICOsahedral Non-hydrostatic General Circulation Model The grid size of the global model can be regionally improved. A first operational version is expected for autumn 2012 resolution: 20 km globaly 5 km for Europe COSMO DE is planned to be improved to 1 km spatial resolution. Ensemble applications are planned for both models. DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 13
  14. 14. RADVOR-OP Radar based precipitation nowcasting up to 2 hours Method: Identification and extrapolation of precipitation areas (tracking) and assessment of cell development Characteristics: Spatial resolution: 1 km Temporal resolution: 5 min / 60 min Updates every 5 minutes (The cell processing method is still in the development stage) DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 14
  15. 15. Communication DWD warnings in the Web Example: Case 3 (Dortmund) The text warning 26 July, 10:00 CEST: … quasi stationary convergency zone from Emsland via Northrhine-Westfalia, Rhineland- Palatinate and Saarland to the Black Forest with Heavy rainfall of more than 40 mm per hour, Hail and heavy wind gusts possible Only slow drift of the thunderstorms with direction north-west. DWD warn map published 26 July 2008, 16:48 CEST DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 15
  16. 16. Communication DWD Hydrometeorological services Close cooperation and joint projects of DWD and the water management authorities Provision of observational data and special forecast products tailored to the need of the water management authorities Consultancy service for water management Regular and special customer meetings Participation in relevant committees Capacity building: Education and training of the users and of students DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 16
  17. 17. Summary Deterministic models provide very good quantitative forecasts up to two days lead time. A 100% certainty will, however, never by possible, especially for the point in time and space of single small scale precipitation and thunderstorm events. Observational data as radar products disseminated (near) realtime provide disaster mangement with quantiative information in order to early react and to reduce damage. New technics: Ensemble forecast provide probabilities. Decision makers need to learn to use this information. DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 17
  18. 18. Additional material 1. Ensemble movie for Case 3 – Dortmund, 26. July 2008 hourly precipitation totals 15:00 -16:00 UTC 2. Weather chart for Case 3 – Dortmund, 26. July 2008 Convergency line as a cause of the extrem rainfall DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 18
  19. 19. COSMO-DE-EPS ensemble predictions with 20 members No. 1 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 19
  20. 20. COSMO-DE-EPS ensemble predictions with 20 members No. 2 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 20
  21. 21. COSMO-DE-EPS ensemble predictions with 20 members No. 3 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 21
  22. 22. COSMO-DE-EPS ensemble predictions with 20 members No. 4 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 22
  23. 23. COSMO-DE-EPS ensemble predictions with 20 members No. 5 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 23
  24. 24. COSMO-DE-EPS ensemble predictions with 20 members No. 6 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 24
  25. 25. COSMO-DE-EPS ensemble predictions with 20 members No. 7 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 25
  26. 26. COSMO-DE-EPS ensemble predictions with 20 members No. 8 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 26
  27. 27. COSMO-DE-EPS ensemble predictions with 20 members No. 9 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 27
  28. 28. COSMO-DE-EPS ensemble predictions with 20 members No. 10 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 28
  29. 29. COSMO-DE-EPS ensemble predictions with 20 members No. 11 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 29
  30. 30. COSMO-DE-EPS ensemble predictions with 20 members No. 12 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 30
  31. 31. COSMO-DE-EPS ensemble predictions with 20 members No. 13 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 31
  32. 32. COSMO-DE-EPS ensemble predictions with 20 members No. 14 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 32
  33. 33. COSMO-DE-EPS ensemble predictions with 20 members No. 15 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 33
  34. 34. COSMO-DE-EPS ensemble predictions with 20 members No. 16 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 34
  35. 35. COSMO-DE-EPS ensemble predictions with 20 members No. 17 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 35
  36. 36. COSMO-DE-EPS ensemble predictions with 20 members No. 18 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 36
  37. 37. COSMO-DE-EPS ensemble predictions with 20 members No. 19 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 37
  38. 38. COSMO-DE-EPS ensemble predictions with 20 members No. 20 COSMO-DE-EPS One hour precipitation total 15:00 -16:00 UTC Dortmund 26. July 2008 Method in development DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 38
  39. 39. Case 3: Local flash flood 2005 DWD Weather chart of 26. July 2008 00 UTC (02 MESZ) DWD -Dpt of Hydrometeorology, B. Rudolf – IGRC Davos 2010 39

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