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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. - PowerPoint PPT Presentation
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Urban Flood Risk Management in a Changing Climate:
Sustainable and Adaptation Challenges
Country Report -Hong Kong, China
ESCAP/WMO Typhoon Committee5th Integrated Workshop
Macao, China, 6-10 September 2010
Hilda LamHong Kong Observatory
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= Short-range Warning of Intense Rainstorms in Localized
Systems• a radar-based nowcasting system operated by HKO sinc
e 1999• 6-min update cycle synchronized with Doppler radars inc
orporating 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 suppo
rt 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
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
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
• In 2010, HKO introduced a new NWP system:• Atmospheric Integrated Rapid-cycle (AIR) f/c mo
del 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
QPF map from 2-km NHM vs. forecast time series at HKO
RAPIDS=Rainstorm Analysis and Prediction Integrated Data-proces
sing 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 ble
nded …)
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
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
Probabilistic rainfall f/c for diff. rain thresholds based on QMORPH global ppt. analysis &
ECMWF EPS perturbed TC tracks
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 HADwith zoom function shown on small panel
Prototype of “Raingauge Black”
Home Affairs Department (HAD) – HAD GOWISEtailor-made wind info.
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
HK Automatic Raingauge Network
Annual TC activities in western North Pacific and South China Sea
0
5
10
15
20
25
30
35
40
45
50
19
61
196
4
196
7
197
0
19
73
19
76
197
9
198
2
198
5
198
8
199
1
19
94
19
97
200
0
200
3
200
6
20
09
No
. of T
C in
wN
P a
nd
SC
S
Annual Total
1960s:35 TCs
after 2000: 27 TCs
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
Annual Typhoon no. making landfall south China coast ~300 km HK 1961-2008
~1 typhoon/year
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
0
500
1000
1500
2000
2500
3000
3500
400019
61
1964
1967
1970
1973
1976
1979
1982
1985
1988
1991
1994
1997
2000
2003
2006
2009
rain
fall
(m
m)
TC rainother rain
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.
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 coast
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
2 2.9 3.3
5 3.1 3.5
10 3.3 3.7
20 3.4 3.8
50 3.5 4.0
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.
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
2 2.9 3.5 4.3
5 3.1 3.7 4.5
10 3.3 3.8 4.7
20 3.4 4.0 4.8
50 3.5 4.1 4.9
Note: mCD = metres above Chart Datum.Chart Datum is 0.146 metre below Principal
Datum.
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.
(courtesy of TVB)
Flooding in Tai O after Typhoon Hagupit (September 2008)
(Image Source: Civil Engineering and Development Department. )
Anti-flood structures