1. 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

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 4 types 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 –introduce 2-km resolution NHM operated on hourly update cycle to provide timely guidance 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 schemes simulate 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 by real-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. RAPIDS Blended QPF – 3 June 2009  importance of blending NWP QPF at diff. lead times (1 hr) verifying radar reflectivity SWIRLS radar-based nowcast RAPIDS blended QFP

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

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 HAD with zoom function shown on small panel

15. Prototype of “Raingauge Black”

16. Home Affairs Department (HAD) – HAD GOWISE tailor-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 5 new locations(x) in New Territories starting 2010

19. HK Automatic Raingauge Network

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

21. Annual TC no. making landfall south China coast ~300 km HK 1961-2008 1960s: 3 TCs 1990-2008: 2.5 TCs 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, TCs contribute ~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 cmsince 1954 IPCC global prediction (2007) 18 – 59 cmby 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. Flooding of the coastal areas becomes easier under tropical cyclone situations Sea level rise, plus storm surge waves caused by typhoon rise in sea level coast

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) Extreme sea-level at Victoria Harbour Return period (year) Extreme sea-level (mCD) based on past data Extreme sea-level (mCD) after a mean sea-level rise of 0.41 m 22.93.3 53.13.5 103.33.7 203.43.8 503.54.0 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. Extreme sea-levels at Victoria Harbour Return period (year) Extreme sea-level (mCD) based on past data Extreme sea-level (mCD) after a mean of sea-level rise of 0.59 m Extreme sea-level (mCD) after a mean of sea-level rise of 1.4 m 22.93.54.3 53.13.74.5 103.33.84.7 203.44.04.8 503.54.14.9 Note: mCD = metres above Chart Datum. Chart Datum is 0.146 metre below Principal Datum.

31. Recorded Tides at Tai Po Kau on 12 January 2005 Spring Tide in Hong Kong 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. (courtesy of TVB) Flooding in Tai O after Typhoon Hagupit (September 2008)

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