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ESCAP/WMO Typhoon Committee 5th Integrated Workshop Macao, China, 6-10 September 2010 Hilda Lam

Urban Flood Risk Management in a Changing Climate: Sustainable and Adaptation Challenges Country Report - Hong Kong, China. ESCAP/WMO Typhoon Committee 5th Integrated Workshop Macao, China, 6-10 September 2010 Hilda Lam Hong Kong Observatory. Contents.

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ESCAP/WMO Typhoon Committee 5th Integrated Workshop Macao, China, 6-10 September 2010 Hilda Lam

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  1. Urban Flood Risk Management in a Changing Climate: Sustainable and Adaptation ChallengesCountry Report -Hong Kong, China ESCAP/WMO Typhoon Committee 5th Integrated Workshop Macao, China, 6-10 September 2010 Hilda Lam Hong Kong Observatory

  2. Contents • Quantitative precipitation estimate (QPE) & quantitative precipitation forecast (QPF) • Current operational arrangement for warning of heavy rain & flooding in HK • Climate Change and Typhoon Committee Activities • Benefit of Typhoons

  3. SWIRLS = Short-range Warning of Intense Rainstorms in Localized Systems • a radar-based nowcasting system operated by HKO since 1999 • 6-min update cycle synchronized with Doppler radars incorporating real-time calibration of: • radar reflectivity • rain gauge data • Tracking algorithms: • TREC (tracking of radar echoes by cross-correlation); • MOVA (multi-scale optical flow by variational analysis) • outputs • SWIRLS outputs (see slide severe wx map of SWIRLS) in support of rainstorm-related warnings • QPF products : flood, landslip warning with DSD & GEO/CEDD • since 2008,GIS-based rainfall nowcast product for PRD (see slide)

  4. Severe weather map of SWIRLS 24 July 2006 • analyzed (solid ellipses) • 30-min nowcast (dashed ellipses) positions of 4types of hazardous wx: • hail • severe wind gusts • heavy rain • cloud-to-ground lightning • “+”, “=”, “o” : • actual lightnings detected

  5. Rainfall nowcast product for Pearl River Delta based on • SWIRLS QPF • open GIS standard of KML nowcast rainfall maps (colour pixels in map window) • can be animated, zoomed, navigated in 3D • by web plugin software optional overlaid on rainfall maps • additional geographical info. • road networks • place names

  6. 2010 new - Atmospheric Integrated Rapid-cycle (AIR) forecast model • In 2010, HKO introduced a new NWP system: • Atmospheric Integrated Rapid-cycle (AIR) f/c model sys. • based on JMA Non-Hydrostatic Model (NHM) • AIR major advancements over RSM: •  model resolution 60km10km for T+72 hr f/c • introduce2-km resolution NHM operated on hourly update cycle to provide timelyguidance to forecasters on high impact weather (include QPF) up to T+15 hr (sample: slide - QPF map) • operation of a 3DVAR data assimilation system & more sophisticated physical parametrization schemessimulate 3-D air flow; cloud, convective processes

  7. QPF map from 2-km NHM vs. forecast time series at HKO

  8. RAPIDS =Rainstorm Analysis and Prediction Integrated Data-processing System • operation since 2005 • 2-km resolution QPF 1-6 hr f/c • optimally blending the SWIRLS &NHM outputs • probabilities of precipitation for various thresholds • by time-lagged ensemble approach • dynamical weightings assigned to SWIRLS/NHM outputs byreal-time verification • phase & intensity correction schemes • correct spatial errors and biases in rainfall intensity • which occasionally found in NHM f/c precipitation (see slides blended …)

  9. SWIRLSradar-based nowcast verifying radar reflectivity RAPIDS blended QFP RAPIDS Blended QPF – 3 June 2009 importance of blending NWP QPF at diff. lead times (1 hr)

  10. SWIRLSradar-based nowcast RAPIDS blended QFP verifying radar reflectivity RAPIDS Blended QPF –3 June 2009 importance of blending NWP QPF at diff. lead times (6 hr)

  11. Probabilistic rainfall f/c for diff. rain thresholds based on QMORPH global ppt. analysis & ECMWF EPS perturbed TC tracks

  12. Current research and development activities on QPE/QPF • upgraded SWIRLS radar tracking algorithm from correlation-based to optical flow-based • operation of a real-time QPF verification system for effective performance monitoring and algorithm tuning • development of a new QPE scheme based on radar-raingauge co-Kriging for better rainfall analysis over gauge sparse areas, as well as potential application to raingauge data QC • a feasibility study to investigate if 1-hour rainfall nowcast could be applied to flood forecasting over a very small catchment area (order of a few sq. km)

  13. Regional rainfall variations could be large Rainfall distribution map (2-3 am on 15 March 2002)

  14. GOWISE - District Rainfall for HADwith zoom function shown on small panel

  15. Prototype of “Raingauge Black”

  16. Home Affairs Department (HAD) – HAD GOWISEtailor-made wind info.

  17. Tai O storm surge alert - Background Flooding at Tai O caused by storm surge during the passage of Hagupit in September 2008 (source: Oriental Daily News / on.cc) Traffic disruption at Lantau cauzed by landslides during the 7 June 2008 rainstorm (source: ISD)

  18. Early Storm Surge Alerts for 5new locations(x) in New Territories starting 2010

  19. HK Automatic Raingauge Network

  20. 1960s: 35 TCs after 2000: 27 TCs Annual TC activities in western North Pacific and South China Sea

  21. 1960s: 3 TCs 1990-2008: 2.5 TCs Annual TC no. making landfall south China coast ~300 km HK 1961-2008 1960s: 3 TCs 1990-2008: 2.5 TCs

  22. Annual Typhoon no. making landfall south China coast ~300 km HK 1961-2008~1 typhoon/year

  23. Climate Change and Typhoon Committee Activities • HKO supported the Typhoon Committee’s initiative in assessing the change in frequency and intensity of TCs in the ESCAP/WMO Typhoon Committee region • in context of climate change • by providing staff • Dr. TC Lee • to serve on its expert team

  24. Climatologically, TCscontribute ~30% rainfall in Hong Kong

  25. Thank you • Lionrock – a mountain • TC named by Hong Kong, China • (Source: CEDD)

  26. Sea level rise Hong Kong 14 cm since 1954 IPCC global prediction (2007) 18 – 59 cm by 2100

  27. Estimates by other independent approaches Simple correlation between sea level and temperature : + 0.5 to 1.4 m Non-linear relation with multiple positive feedback : + 0.8 to 2 m Sources : Rahmstorf, S., 2007. A Semi-Empirical Approach to Projecting Future Sea-Level Rise. Science 315, 368–70. Pfeffer, W.T., J.T. Harper and S.O. Neel, 2008. Kinematic Constraints on Glacier Contributions to 21st-Century Sea-Level Rise. Science 321, 1340 – 1343.

  28. Sea level rise, plus storm surge waves caused by typhoon rise in sea level coast coast Flooding of the coastal areas becomes easier under tropical cyclone situations

  29. Table 1 : Magnitude of extreme sea levels at Victoria Harbour based on past data and a projected rise of 0.41 m (due to thermal expansion of seawater alone) Note: mCD = metres above Chart Datum. Chart Datum is 0.146 metre below Principal Datum.

  30. Magnitude of extreme sea levels at Victoria Harbour based on past data, a projected rise of 0.59 m and of 1.4 m. Note: mCD = metres above Chart Datum. Chart Datum is 0.146 metre below Principal Datum.

  31. Spring Tide in Hong Kong           Recorded Tides at Tai Po Kau on 12 January 2005 Spring Tide : Near New Moon or Full Moon each month, the Earth, Moon and Sun are aligned along a straight line and the sea-level rise and fall will have a larger range.

  32. Flooding in Tai O after Typhoon Hagupit (September 2008) (courtesy of TVB)

  33. Anti-flood structures (Image Source: Civil Engineering and Development Department. )

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