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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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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


Qpf map from 2 km nhm vs forecast time series at hko
QPF map from 2-km NHM vs. forecast time series at HKO


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)


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)


Regional rainfall variations could be large

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


Gowise district rainfall for had with zoom function shown on small panel
GOWISE - District Rainfall for HADwith zoom function shown on small panel




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)


Early storm surge alerts for 5 new locations x in new territories starting 2010
Early Storm Surge Alerts for 5new locations(x) in New Territories starting 2010



Annual tc activities in western north pacific and south china sea

1960s:

35 TCs

after 2000:

27 TCs

Annual TC activities in western North Pacific and South China Sea


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


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


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


Climatologically tcs contribute 30 rainfall in hong kong
Climatologically, TCscontribute ~30% rainfall in Hong Kong


Thank you
Thank you

  • Lionrock – a mountain

  • TC named by Hong Kong, China

  • (Source: CEDD)


Sea level rise

Hong Kong 14 cm since 1954

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


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.


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


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.


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.


Spring Tide in Hong Kong past data, a projected rise of 0.59 m and of 1.4 m.

          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.


F past data, a projected rise of 0.59 m and of 1.4 m.looding in Tai O after Typhoon Hagupit

(September 2008)

(courtesy of TVB)


Anti-flood structures past data, a projected rise of 0.59 m and of 1.4 m.

(Image Source: Civil Engineering and Development Department. )


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