Transcript Review of Tropical Cyclone Signal System and Warning Services

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
• 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
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
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
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
QPF map from 2-km NHM vs.
forecast time series at HKO
RAPIDS
=Rainstorm Analysis and Prediction Integrated Dataprocessing 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 …)
RAPIDS Blended QPF – 3 June 2009
 importance of blending NWP QPF at diff. lead times (1 hr)
SWIRLS radar-based
nowcast
verifying radar reflectivity
RAPIDS blended QFP
RAPIDS Blended QPF –3 June 2009
 importance of blending NWP QPF at diff. lead times (6 hr)
SWIRLS radar-based
nowcast
RAPIDS blended QFP
verifying radar reflectivity
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 radarraingauge 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
Prototype of “Raingauge Black”
Home Affairs Department (HAD) – HAD GOWISE
tailor-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
Traffic disruption at Lantau cauzed by
landslides during the 7 June 2008
rainstorm
(source: Oriental Daily News / on.cc)
(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
Annual Total
North Pacific and
South China Sea
Annual Total
45
40
35
30
25
20
15
10
5
1960s:
35 TCs
after 2000:
27 TCs
2009
2006
2003
2000
1997
1994
1991
1988
1985
1982
1979
1976
1973
1970
1967
1964
0
1961
No. of TC in wNP and SCS
50
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
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
4000
TC rain
other rain
3500
2500
2000
1500
1000
500
2009
2006
2003
2000
1997
1994
1991
1988
1985
1982
1979
1976
1973
1970
1967
1964
0
1961
rainfall (mm)
3000
Thank you
•
•
Lionrock – a mountain
TC named by Hong Kong, China
•
(Source: CEDD)
Sea level rise
Hong Kong
14 cm
IPCC global prediction (2007) 18 – 59 cm
since 1954
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
coast
rise in sea level
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)
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.
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.
Flooding in Tai O after Typhoon Hagupit
(September 2008)
(courtesy of TVB)
Anti-flood structures
(Image Source: Civil Engineering and Development Department. )