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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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slide1

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

contents
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
swirls
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)
severe weather map of swirls
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
rainfall nowcast product for pearl river delta
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
2010 new atmospheric integrated rapid cycle air forecast model
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
rapids
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 …)
rapids blended qpf 3 june 2009 importance of blending nwp qpf at diff lead times 1 h r

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)
rapids blended qpf 3 june 2009 importance of blending nwp qpf at diff lead times 6 h r

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)
slide11
Probabilistic rainfall f/c for diff. rain thresholds based on QMORPH global ppt. analysis & ECMWF EPS perturbed TC tracks
current r esearch and development activities on qpe qpf
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)
slide13

Regional rainfall variations could be large

Rainfall distribution map (2-3 am on 15 March 2002)

slide17

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)

annual tc no making landfall south china coast 300 km hk 1961 2008

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

climate change and typhoon committee activities
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
thank you
Thank you
  • Lionrock – a mountain
  • TC named by Hong Kong, China
  • (Source: CEDD)
slide26

Sea level rise

Hong Kong 14 cm since 1954

IPCC global prediction (2007) 18 – 59 cm by 2100

slide27

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.

slide28

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

slide29

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.

slide30

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.

slide31

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.

slide32

Flooding in Tai O after Typhoon Hagupit

(September 2008)

(courtesy of TVB)

slide33

Anti-flood structures

(Image Source: Civil Engineering and Development Department. )

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