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1
Enhancing Slope Safety
Preparedness for Extreme Rainfall
and Potential Climate Change
Impacts in Hong Kong
Ken Ho, HW Sun, Alan Wong & CF YamGeotechnical Engineering Office
SM LeeHong Kong Observatory
2
Intense urban
development
High seasonal
rainfall
Steep terrain Tropically
weathered profile
Urban slope engineering -
Challenges in Hong Kong
Lack of geotechnical engineering input before 1977
“The Building Authority will offer no objection to
an angle of slope 35 for filling and 50 for cutting”
“Deposited fill in 5 ft. layerand compacted
subjected to approval bythe Engineer as a result of
compaction trials”
1972 Po Shan landslides(69 fatalities)
1972 & 1976 Sau Mau Ping landslides
(90 fatalities)
Resulted in serious urban landslide problems (rain-induced)
3
Mid-1990s
1977
Empirical
Slope Engineering
Geotechnical
Slope Engineering
Evolution of Slope Engineering andLandslide Risk Management in Hong Kong
GEO set up
Enhanced Landslide
Risk Management
4
Aerial photograph
interpretation
Ground investigation
Soil & rock logging
Engineering geological mapping
Undisturbed sampling
Laboratory testing
Geological and groundwater
models
Limit equilibrium
analysis
Numerical modeling
5
Enhanced Slope Engineering Practice
Enhanced Landslide Risk Management (mid-1990s to now)
Formal risk assessment
and management
Slope maintenance
Systematic landslide investigations
More than 2,700
landslides examined and
more than 200
landslides selected for detailed
study since 1997
Public education
Landslip warning system
Hong Kong Slope Safety System
Goals
1. To reduce landslide risk to the community (i.e. primarily to save lives) through a policy of priority and partnership.
2. To address public perception and tolerability of landslide risk in order to avoid unrealistic expectations.
7
Key Result Areas
1. Set slope safety standards and improve practice
2. Ensure safe standard of new slopes
3. Rectify existing substandard Government man-made slopes
4. Maintain all sizeable Government man-made slopes
5. Ensure owners take their responsibility for slope safety
6. Promote public awareness, preparedness and response ………
7. Improve slope appearance
8
Holistic Slope Safety System in Hong Kong
Contribution by each component
to reduce landslip risk Slope Safety System components
hazard vulnerability
to address public attitudes
Policing
statutory provisions, safety screening and statutory repair orders for slopes
checking new slope works
slope maintenance audit
inspecting squatter areas and recommending safety clearance
input to land use planning
Safety standards R&D
[e.g. slope catalogue and landslide inventory
natural terrain hazard assessment and mitigation
debris mobility
landslide risk assessment and management
slope greening]
9
Holistic Slope Safety System in Hong Kong
Contribution by each component
to reduce landslip risk Slope Safety System components
hazard vulnerability
to address public attitudes
Systematic investigation, works and maintenance programme
investigation serious landslides
upgrading Government man-made slopes
mitigating natural terrain landslide risk
Public warning, education and information services
landslip warning and emergency services
maintenance campaign
personal precautions campaign
awareness programme
information services
Note: Maintain all registered Government man-made slopes and natural terrain defence/stabilisation measures.
1977 2000 2010 Year
An
nu
al
lan
dsl
ide
fata
liti
es
0
10
20
FA
C
Holistic Landslide Risk Management
Risk escalation with urban
development
Actual risk trend
Set
ting u
p o
f G
EO
Retrofitting substandard slopes (hard measures)
Regulating new works
Non-works (soft)
measures
E
X
BD
10
Squatter clearance
(4) to (6) Promote public awareness and response through public education, information services & public warnings
(Non-works Risk Management Measures)
Landslip warning & emergency service
Public education Information & community
advisory service
11Partnership with the public and other stakeholders
Percentage of the 37,000 ‘Old’ Slopes
(ranked according to facilities affected)
Percen
tag
e o
f O
vera
ll R
isk
-to
-lif
e
RISK PROFILE OF 37,000 ‘OLD’ SLOPES
Pe
rc
en
tag
e o
f O
ve
ra
ll R
isk
-to
-lif
e
Group (5)Country park,minor roads
RISK REDUCTION BY UPGRADING ‘OLD’ SLOPES
US$US$
1 1 MM
perper
lifelife
Percentage of All Pre-1977 Slopes
(ranked according to facilities affected)
(4)
(3)
(2)
Group (1) Residential buildings,
major roads
(1) By year 2000, reduce landslide risk to less than 50% of that in
1977
(2) By year 2010, further reduce
overall risk to less than 25% of that
in 1977
Landslide Risk Reduction Targets
(X)
(E)
12Government’s public safety goals
pledged in CE’s Policy Address
The holistic slope safety system in Hong Kong mainly caters for landslides triggered by heavy rain on both substandard man-made slopes and natural vulnerable hillsides
24-hr rainfall in 22.5.2013 rainstorm (53 landslides)
~10%annual rainfall
Heavy but
not
extreme
rainfall
13
Landslide Risk Management
Quantitative Risk Assessment (QRA) and
risk management
Assessment & mitigation of landslide consequence
Slope engineering works aim to prevent failure,
thereby reduce risk
Risk = Likelihood of failure
Consequence of failure
14
Natural Terrain Failure
Propensity ~ 1 / km2 /yr
Potential Loss of Life (PLL)
~ 5 /yr
Man-made Slope Failure
Propensity ~ 1 / km2 /yr
Potential Loss of Life (PLL)
~ 22 /yr in 1977
~ 10 /yr in 2000
~ 4 /yr in 2010
60% steep natural hillside and 39,000 pre-1977 man-made slopes
15
16
Natural Terrain Landslides
17
Many landslides
in a heavy rainstorm
(landslide preventive works
not practical/cost effective/
environmentally friendly)
Marginal stability
and small shallow
failures can be
serious in Hong Kong
Increasing risk
due to developments
closer
to natural hillsides
Low-frequency
large-magnitude events
Debris slide/ avalanche
on open hill slope Debris avalanche/flow
along a topographic depression
Channelized debris flow along a drainage line
Increasing debris mobility
Natural Terrain Landslides (1 to 2 per km2 per yr)
18
NaturalTerrainHazardStudy
Guidelines
SPR No. 1/2002
RiskGuidelines
andCriteria
GEO RptNo. 75
Designof
Debris-resistingBarriers
GEO RptNo. 104
All Sites
Sites Requiring
Hazard Mitigation
investigation,
assessment,
design
screening
19
Advances in Professional Practice in
Natural Terrain Landslide Risk Management
Regolith
Mapping
Geomorpholog
ical
Assessment
Debris
Mobility
Bioengineeri
ng
Mitigation &
Prescriptive
Measures
GIS & IT
Age-datingQRA
Magnitude-
Frequency
correlation
20
GeographicInformation
System(GIS)
Application of Digital Technologies
Internettransmissiontechnology
Global PositioningSystem (GPS) &
mobile communication
Pocketcomputer
Data
(spatial)
Image Remote-sensing
information
Digitalphotogrammetry
Otherremote-sensing
techniques
21
22
3D debris mobility analysis
FLO-2D3D-DMM (Kwan & Sun)
• Simulate debris runout path in addition to runout distance
• Model lateral influence zone, debris geometry
• Allow splitting and merging of debris
Post-2010 Landslip Prevention and Mitigation Programme announced in 2007
Mitigate risk at 30 nos. vulnerable natural hillside catchments and upgrade 150 substandard government man-made slopes
HK$ 500 million for natural terrain risk mitigation & HK$500 million for man-made slopes upgrading
Annual Output of LPMitP
23
“As Low As Reasonably
Practicable” (ALARP) Zone
Year
Landslide risk
Slope Safety System
not in place
Risk increase due to new works with no geotechnical control
Risk Trend
Risk increase due to slope degradation & population growth [+ possible climate change effect]
LPMitP to contain risk
2010
SSMS to reduce risk
Slope Safety System
1977
Landslip Prevention and Mitigation Programme
24
25
Were we being
overly confident or complacent?
In 2007, Nordie Morgenstern wrote in
the Foreword: “In his seminal Terzaghi
Lecture, Bjerrum (1967) told us of the
frustration experienced by a
geotechnical engineer in Japan when
dealing with landslides who concluded
that “a landslide devil seems to laugh at
human incompetency”. The progress
recorded in this Memorial Volume
assures us that, at least, the landslide
devil is no longer laughing in Hong Kong”
26
2013 Typhoon Wipha in Japan (41 fatalities)
2009 Typhoon Morakot in Taiwan (~650 fatalities)
2010 Rainstorm in Gansu(>1,400 fatalities)
2011 Rainstorm in Brazil(>900 fatalities)
Extreme Weather-related Landslide Disasters around the Globe
June 2008 Rainstorm (return period >1,000 yrs)triggered about 2,500 natural terrain landslides & 2 fatalities
Massive and long runout debris flows
Village house evacuations
Road closure Building Evacuations
27
June 2008 Lantau Rainstorm (~ 60% PMP)
Escalated natural terrain landslide density (>2,500
nos.)
Under prediction of debris runout
28
> 20% annual rainfall
Actual landslide(1,800 m3)
Design event (150 m3)
Adverse settings for mobile and sizeable CDF with
watery debris
• Confluence of multiple sources
• Significant entrainment
• Large and steep drainage line
• Sizeable catchment area• Large source volume
• Deep-seated failure
• Large rock slide
• Spatially extensive shallow slide
• Extensively cracked area
• Discharge of debris into
running water (e.g. a large
drainage line)29
Hig
he
st h
ou
rly
ra
infa
ll r
eco
rd（
mm
）
Highest hourly rainfall (in mm) recorded at HK Observatory（1885 - 2011）
30
Extreme rainfall events are becoming more frequent –empirical evidence
31
Strategy Adopted in Hong Kong
Collaborate with meteorological experts to understand
changing weather patterns & examine nature and
magnitude of extreme rainfall
Enhance understanding of corresponding extreme
landslide scenario and impact to community
Review capacity of emergency response system
Strengthen crisis preparedness, emergency response
and enhance community awareness and resilience
32
Past and projected annual rainfall anomaly of Hong Kong under the RCP8.5 scenario
Note: Likely range refers to the region embraced by the 5th and 95th
percentiles of the multi-model ensemble (considerable uncertainties)
Extreme rainstorm
events in 21st century1. More frequent & more intense
2. Increased variability
Findings of Downscaling Studies in Hong Kong
Scenario based Assessment of
Extreme Landslide Scenarios
33
Extreme landslide scenarios are characterized by:
(a) Widespread landslides with increased propensity,
scale and mobility of failure resulting in serious
damage and casualties
(b) Low frequency, large magnitude landslides [which
are liable to overwhelm mitigation measures]
(c) The large number of landslides and affected
population, together with breakdown of infrastruture
and the ongoing nature of landslide hazards, pose a
grave challenge to the response & recovery work
• Need not just rainfall intensity & duration, but also areal
extent and spatial location of extreme rainstorms
• Current state-of-the-art of downscaling studies have
uncertainties and limitations [give broad trends at best]
• Pragmatic approach : PMP taken as benchmark to help
define/contextualize plausible extreme rainfall events
• Level 1 event - Near-miss event (at extreme of
historical/statistical distribution) in recent past taken to
hit a densely populated area [1,000-yr]
• Level 2 event - A simulated rainstorm with allowance for
climate change effect by end of 21st century (increase in
typhoon rainfall); more severe and rare, but plausible
event [10,000-yr]
1. Extreme Rainfall Events
34
24-hr rainfall (mm)
Aff
ecte
d a
rea
(km
2) PMP1999
Probable Maximum Precipitation (PMP)
(2) Level 2 :
85% PMP1999
(~10,000-yr)
based on HKO (1999)
(1) Level 1 : 60% PMP1999
(~1,000-yr event)e.g. 2008 Lantau rainstorm
35
10
100
1000
10000
0 200 400 600 800 1000 1200 1400 1600 1800
Are
a (
km
2)
Rainfall (mm)
June 2008 Storm
Updated PMP
old PMP by HKO in 1999
36
Probable Maximum Precipitation (PMP) Estimate for Hong Kong – Theoretical Upper Limit of Rainfall Depth
2014 Updated PMP
Extreme rainfall scenario 1: Near-miss Event
37
Transposing June 2008 rainstorm
to strike Hong Kong Island
~ 1 in 1,000-year return period
38
Extreme rainfall scenario 2:More Extreme Event
Transposing 2009 Typhoon
Morakot rainstorm to hit
Hong Kong Island with
suitable orographic
corrections & allowance for
climate change by end of
21st century
70% 2014
PMP
Notional return
period of
10,000 years
under current
climate
condition
~
~
© 2011 Google
Level 2 Extreme Rainstorm based on 70% of the PMP2014
hitting Hong Kong Island
39
• Hillside & slope response : make reference to
rainfall-landslide correlations for natural terrain
and man-made slopes respectively + judicious
extrapolation to cover extreme rainfall
• Debris scale and debris mobility : probabilistic
assessment based on data from June 2008
severe rainstorm + extrapolation (adjustment)
• Landslide impact – use Quantitative Risk
Assessment (QRA) model to assess societal
risk
2. Extreme Landslide Scenarios and Impact
to serve as ‘Stress Testing’ of system
40
Normalised Rainfall intensity = rolling max. 24-hour rainfall/mean annual rainfall
Den
sity
of
NT
lan
dsl
ide
(No
./km
2 ) Scenario 2Scenario 1
1966HK Island
(64 dead, >2000 homeless, >8600
evacuated)
Landslides ~2,000Serious ~200-300
Landslides ~50,000Serious ~4,000-9,000
41Findings included in Hong Kong Climate Change Report 2015
42
Extreme Weather-related Landslide Disasters in Hong Kong
1966 Rainstorm hitting HK Island(64 dead, >2000 homeless, >8600 evacuated)
Stubbs Rd North Point
North Point
Mid-levels
Mid-levels
Extreme Rainfall
(Scenario 1)
Extreme Rainfall
(Scenario 2)
Landslides ~2,000(Serious 200-300)
Landslides ~50,000(Serious 4,000-9,000)
~ 250-300
Capacity limit of existing system
Existing emergency system stretched to the limit
Capacity of existing system grossly overwhelmed!
Need a new strategy to enhance emergency preparedness and resilience
Streamlining to remove bottleneck (e.g. transport, communication,
mode of operation, manpower, etc)
Heavy rainstorms(frequent)
43
44
GEO Landslide Emergency Service
• @150 geotechnical engineers take part in landslide emergency system on a roster basis to provide 24/7 emergency service
• When a Landslip Warning is issued (based on actual rainfall and forecast rainfall), GEO Emergency Control Centre will be mobilised
• Upon receipt of a reported landslide, geotechnical engineers will be dispatched to the landslide site, assess the slope failure and residual risk, & give professional advice on emergency responses (evacuation, road closure, diversion of surface water, etc.)
45
Potential Bottlenecks in GEO’s Emergency System
• Lack of transportation
• Inaccessibility to landslide sites
• Logistics for triple emergency team operation
• Personal safety during adverse weather
• Breakdown of communication (power supply or
mobile network)
• Limited man-power resources
• Little hands-on experience of new staff
• ………….etc.
Lan
dsl
ide
den
sity
(log s
cale
)
Heavy rain
Ris
k d
ensi
ty
Un-engineeredman-made
slopes failures
Natural terrainlandslides
24-hr 20% annual rainfall
Extreme rain
Rainfall (reducing prob. of occurrence)
Rainfall (reducing prob. of occurrence)
Landslides under extreme weather conditions
46
Natural terrainMan-madeslopes
• Empirical evidence (e.g. recent record-breaking
rainstorms), downscaling studies and above scenario-
based assessments point to extreme event does pose
a major concern for landslide risk management
• Better understanding of nature & scale of problem
associated with extreme rainstorms : holistic slope
safety system developed primarily to address heavy
rainstorms is not adequate for extreme rainfall events
• Stress testing of emergency response system – a new
strategy of emergency preparedness & response is
needed to supplement the existing approach
Insights from Scenario-based Assessments
47
• Major uncertainties involving unknown-
unknowns in respect of hillside response and
landslide consequence (potential for collapse of
multi-storey building blocks due to debris impact
cannot be discounted)
• Can the risk associated with extreme events be
quantified reliably?
• Preliminary and rough QRA : 50% increase in
overall risk due to consideration of extreme
events, but estimate is subject to considerable
uncertainties. The concern is mainly on the
increased likelihood of multiple fatalities
(implications on F-N curve)
3. Implications of Extreme Events on Risk Level
48
Enhancing slope safety preparedness for extreme
weather events requires risk management approach
• It is not just a question of assessing whether failure will occur but also how many failures, their potential scales, mobility, travel paths, elements at risk, consequence of failure/debris impact, etc.
• A systems-based approach making the best use of good quality field data to assess the nature and overall scale of the problem through extrapolation helps to review the necessary risk management actions and formulate suitable strategy/policy
• A physics-based approach is more suited to assessing the potential response of an individual slope but ….. 49
Mitigating and Adapting to
Extreme Events/Climate Change
50
Strategy for Managing & Adapting to
Extreme Events/Climate Change
• Prevention:
• Mitigation:
improve emergency management and enhance community resilience*
enhance design guidelines / robustness of
engineering measures
implement mitigation measures for
‘hot-spots’ (e.g. upgrading / defensive
works)• Preparedness:
• Response:
• Recovery:
* Essential and most effective strategy
51
Promulgate appropriate design, construction, supervision and maintenance standards
Enhanced robustness of engineering works and use of
prescriptive drainage provisions as contingency measures for
more redundancy + improved drainage detailing are strongly
promoted
To reduce chance of occurrence of
significant slope failures and major
failure consequence
Engineering Approach - Prevention
52
Engineering Approach – Mitigation
Upgrade 150 substandard man-made slopes
Mitigate risk of 30 vulnerable natural hillside catchments
Landslip Prevention and Mitigation Programmeannual targets (risk-based priority ranking system):
53
Retrofit existing man-made slopes & undertake risk mitigation works for natural terrain affecting existing buildings & important transportation corridors
Prevention(enhance slope
engineering practice and robustness of
engineering measures)
Mitigation(implement landslip
mitigation measures, e.g. slope upgrading & risk
mitigation works)
Are these good enough for extreme rainstorms?
54
Should the required safety margin of engineering works
be raised?
How bad can it get under extreme
rainstorms in terms of landslide
propensity, scale and debris
mobility?
Note : It may be useful to contain the damage by attending to risk ‘hot spots’ (esp.
those that are liable to give rise to low-frequency, large magnitude events), but
engineering works are generally not effective and not good value for money in
combating widespread landslides in an extreme event.
Strategy for Managing Extreme Events
Preventionenhance slope
design & practice
Mitigationimplement landslip
mitigation measures(e.g. upgrading & retrofitting works)
Preparedness
ResponseRecovery
To improve emergency management and
community preparedness,
response & resilience *
* Essential and most effective strategy for extreme events
55
2009 Typhoon Morakot 莫拉克(653 fatalities; Loss US$ 3.3 Bs)
2012 Typhoon Sandy 桑迪(72 fatalities; Loss US$ 65 B)
“… they should have been evacuated much earlier”
“…just because they stayed “
“… please listen; when they tell you to evacuate, you need to evacuate”
“… don’t pause; don’t question the instruction”
vs
Emergency Preparedness and Response
56
To enhance community resilience in facing extreme landslide scenariosand equip people with knowledge and skills for self-help
57
(1) Raise Public Awareness and Enhance Public Education and Crisis Communication
“If disasters occur in Hong Kong, the public must cooperate with the Government’s emergency
response actions”
Enhancing Emergency Preparedness
Self protection and neighbourhood support
58
(2) Key Messages to the Public
999
Enhancing Emergency Preparedness
Normal days: Be familiar with the messages on warning signs for slopes
If feel threatened by landslide: • Go to upper floors;• Call Police for help;• Leave for a safe shelter if
considered safe to do so
During heavy rainfall: Stay as far away from steep slopes as possibleAvoid hilly roads as far as possible
• Promote bottom-up approach (empower & facilitate public to make decisions)
• Information dissemination – reliable information hub known to the public
• Role of social media for disaster communication and coordination
(3) Evacuation Plan
Dwellings close to natural hillside
Low-lying Area subject
to flooding
Evacuation route59
Enhancing Emergency Preparedness
Well planned evacuation routes, assembly points, temporaryshelters, and logistic arrangements [+ drills to integratecommunities & foster trust in government]
60
(4) Enhancing Government Emergency Services
• Streamline emergency management procedures and practice for dealing with extreme events, address potential bottlenecks and build in more redundancy
• Improve coordination, exchange information, and brainstorm improvement measures through regular inter-departmental meetings and learn the lessons from past events
• Emergency drills to test and improve the emergency response and capability
Emergency Drill
Enhancing Emergency Preparedness
• Increasing use of social media & mobile technology by the public for disaster communication & coordination
61
(5) Enhanced Sharing of Emergency InformationEnhancing Emergency Preparedness
Incident Response
FinanceLogisticsPlanningOperations
CommandIncident Public Awareness
• Common Operational Picture (COP) – an IT platform powered by web based GIS which offers a consistent and easy to understand overview of the changing situations of reported emergency incidents
• Facilitate stakeholders to make effective, informed and timely decisions and promote collaboration
• Enhance public communication and public messages
62
10
0.0001
0.001
0.01
0.1
1
<50 50-100
100-150
150-200
250-300
300-350
350-400
400-450
200-250
>=450
Retaining Walls
Rolling 24-hour rain
10
0.0001
0.001
0.01
0.1
1
<50 50-100
100-150
150-200
250-300
300-350
350-400
400-450
200-250
>=450
Rock Slopes
10
0.0001
0.001
0.01
0.1
1
<50 50-100
100-150
150-200
250-300
300-350
350-400
400-450
200-250
>=450
Fill Slopes
10
0.0001
0.001
0.01
0.1
1
<50 50-100
100-150
150-200
250-300
300-350
350-400
400-450
200-250
>=450
Cut Slopes
Pro
bab
ilit
y o
f fa
ilu
res
Rolling 24-hour rain
Pro
bab
ilit
y o
f fa
ilu
res
Pro
bab
ilit
y o
f fa
ilu
res
Pro
bab
ilit
y o
f fa
ilu
res
Rolling 24-hour rainRolling 24-hour rain
800,000 807,500 815,000 822,500 830,000 837,500 845,000 852,500 860,000800,000
806,000
812,000
818,000
824,000
830,000
836,000
842,000
848,000
0mm
50mm
100mm
150mm
200mm
250mm
300mm
350mm
400mm
450mm
500mm
550mm
600mm
650mm
700mm
750mm
800mm
850mm
21 hours real-time rainfall
+ 3 hours forecast rainfall or
24-hr real-time
rainfall (spatial distribution)
800,000 807,500 815,000 822,500 830,000 837,500 845,000 852,500 860,000800,000
806,000
812,000
818,000
824,000
830,000
836,000
842,000
848,000
0.0 no.
0.1 no.
0.5 no.
1.0 no.
1.5 no.
Predicted No. of landslides (15 as Landslip Warning
Trigger Level)
Landslip Warning System in Hong Kong
Rainfall-landslide
correlations
Spatial distribution of man-made
slopes
Figure 9 - Extrapolation of Natural Terrain Landslide Density
0.01
0.1
1
10
100
1000
0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.450 0.500
Normalized Maximum Rolling 24-hour Rainfall
Log
(Sto
rm-b
ased
Lan
dslid
e D
ensit
y)
Max. 24-hr / Mean Annual Rainfall
0% 10% 20% 30% 40%
1,000
100
10
1
0.1
0.01
Rainfall - Natural Terrain Landslide Correlation
1990
Tsing Shan
debris flow
(20,000 m3)
1993
Lantau
Landslides
(850+ nos.)
1966 rainstorm
Probable Maximum
Precipitation (PMP)
~10,000 landslides in 10 km2
(10 - 20% area detachment)
63
64
Predicted number of
Natural Terrain
Landslides
Alert
LevelScenarios
≥ 500 to < 1000 1Alert of possible widespread
natural terrain landslides
≥ 1000 to < 2000 2Warning of widespread
natural terrain landslides
≥ 2000 3Warning of very widespread
natural terrain landslides
Natural Terrain Landslip Alert Criteria formulated to
enhance fore-warning and landslide emergency
mobilization with prediction of widespread landslides
65
Concurrent Occurrence of Multiple Hazards
Landslides, flooding, storm surges, tree falls, damage to squatter huts and buildings by severe typhoons, breach of reservoirs or catchwaters, damage to port facilities by sea waves, etc. are hazards that are liable to occur concurrently and may lead to cascading consequences.
This has major implications for those agencies involved in emergency response (e.g. Fire Services Department, Police, etc.).
66
• What extreme events & multiple hazards to prepare for?
• What happens when the emergency service capacity is overwhelmed?
• What if the key infrastructure (e.g. transport, electricity,
mobile and internet connection) also breaks down?
• To cater for possible evacuation of how many people?
• How to efficiently and safely evacuate them?
• Where to temporarily house these people? How to supply their basic needs?
• Critical infrastructure (e.g. MTR) to protect?
• Major gap prevails in community awareness and engagement in disaster preparedness activities
Key Emergency Issues Requiring Attention
Concluding Remarks
Engineering Meteorological
A more resilient city
67
Multiple disciplines/sectors
(e.g. medical, social service, etc.)
General public
• Climate Change => extreme events more likely & more intense• Neither practicable nor cost effective to rely solely on engineering
works to manage the risk of extreme rainfall scenarios• Gear up crisis preparedness, emergency response and recovery for
potential impact of extreme rainfall and multiple hazards• A strategy involving partnering, self protection and neighbourhood
support is called for
How best can we tame the landslide devil?
Not possible without the concerted efforts by the
profession
We need to further gear up to meet the formidable challenges in
discharging our due diligence
68
Thank you
69
Resilience
The capacity to withstand the impact
of rare adverse events and the ability
to recover quickly after the impact
70
71
Tsunami Hazard at Osaka Prefecture
Scenario assessed: Magnitude 9 earthquake off the coast of Japan
Hazard: 20 m high tsunami attacks Osaka within 2 hrs; max. 34.4 m at worst location (黑潮町)
Consequence: 130,000 fatalities; which may reduce to 8,800 if people were to take emergency action after the earthquake
…… Japanese government
emphasizes importance of
community cooperating with
government in response to advice
on early evacuation
72
Many landslides
in a heavy rainstorm
(landslide preventive works
not practical/cost effective/
environmentally friendly)
Small failures can be
serious in HK
Increasing risk
due to developments closer
to natural hillsides
Low-frequency
large-magnitude events
Debris slide/ avalanche
on open hill slope Debris avalanche/flow
along a topographic depression
Channelized debris flow along a drainage line
Increasing debris mobility
Natural Terrain Landslides (1 to 2 per km2 per yr)
73
74
June 2008 debris flows more mobile than ENTLI
75
Climate Change Studies by Intergovernmental Panel
on Climate Change (IPCC)
Fourth Assessment Report by IPCC (2007):
Asia will become warmer and wetter
Summer precipitation is predicted to increase in East
Asia
Frequency of intense precipitation events is likely to
increase
Increase of tropical cyclone activities in East Asia
76
• Trend analysis (extrapolation based on the observed trends from historical records)
• Statistical downscaling of AOGCM projections (empirical approach via relationship between atmospheric variables and regional/local surface variables)
• Dynamical downscaling of AOGCM projections (Based on climate physics and nests a higher resolution Regional Climate Model RCM with a coarser resolution GCM)
Methods of Projecting Climate Change Effects
77
Uncertainties in Climate Change Projections
Inadequate understanding of physical processes (cloud
microphysics, small-scale turbulence, etc.)
Inherent variability
Modeling errors
Uncertainty in emission of greenhouse gases & aerosols
Different GCM’s and downscaling methods liable to give a
wide range of predictions of differing resolution
Uncertainty due to anthropogenic influences
Tropical monsoon rainfall predictions more uncertain
(modeling of squall lines & thunderstorms)
78
Updating of PMP
• To update both 4-hr PMP and 24-hr PMP
estimates with storm transposition and
orographic adjustments in addition to moisture
maximization technique
• To adopt storm separation technique (e.g. Step
Duration Orographic Intensification Factors
(SDOIF) method to decompose the transposed
rainstorms into convergence and orographic
components
79
Approach to Adapting to Climate Change
Pragmatic and incremental approach
Use robust stabilization & mitigation measures to enhance resilience to extreme rainfall
Contingency measures (e.g. prescriptive drainage provisions) to build in more redundancy
Improve detailing of mitigation measures & drainage provisions to reduce vulnerability
Public education & effective risk communication
80
Additional 200 HLC
Extended Criteria for HLC
Notes:
1. ENTLI landslides (relict or recent) or confirmed
landslide incident.
2. Facility includes buildings, major roads and mass
transportation infrastructures.
3. Use 40% of the debris trail length or 40 m,
whichever is larger.
Criterion (1a): Criterion (1b):
Criterion (2):
Concerns
81
• Landslides: serious consequences + breakdown of
existing emergency system
• Other hazards: likely to be similar situation
• Compounding effects of concurrent occurrence of
multiple hazards
• Liable to be aggravated by climate change and
continued population increase/urban development
Are we adequately prepared for extreme events ?
82
Reminder from 1972 Po Shan Landslide (67 fatalities)
Slow in evacuation 3 months to clear the scene
Sham Tseng San Tsuen‘React-to-known-hazard’
1 fatality & 13 people
injured
Checkdam
Potentiallandslidesource
(1400 m3)
design volume
83
84
Debris Mobility - analytical assessment (2D)
• DAN (Hungr, 1995)
• 2D-DMM (HW Sun)
85
3D debris mobility analysis
FLO-2D3D-DMM (Kwan & Sun)
• Simulate debris runout path in addition to runout distance
• Model lateral influence zone, debris geometry
• Allow splitting and merging of debris
Figure 9 - Extrapolation of Natural Terrain Landslide Density
0.01
0.1
1
10
100
1000
0.000 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.450 0.500
Normalized Maximum Rolling 24-hour Rainfall
Log
(Sto
rm-b
ased
Lan
dslid
e D
ensit
y)
Max. 24-hr / Mean Annual Rainfall
0% 10% 20% 30% 40%
1,000
100
10
1
0.1
0.01
Rainfall - Natural Terrain Landslide Correlation
1990
Tsing Shan
debris flow
(20,000 m3)
1993
Lantau
Landslides
(850+ nos.)
1966 rainstorm
Probable Maximum
Precipitation (PMP)
~10,000 landslides in 10 km2
(10 - 20% area detachment)
86
87
Enhanced Strategy and Preparation
Source: 台灣水土保持局土石流防災中心
災害防治工作基本理念
88
Enhanced Community Resilience
89
In case of debris
flows:
1 ……
2 ……
3
4 ……
Educate and enable the public to look after themselves
90
(http://www.wretch.cc/blog/billypan101/16017779)
2009 Typhoon Morakot web-based information on
1200 disaster spots by Billy Pan and the public
91
Intergovernmental Panel on Climate Change, (IPCC)
“Extreme weather includes
unusual, severe or unseasonal weather;
weather at the extremes of the historical distribution
– the range that has been seen in the past”
“… charts the occurrence of specific extreme events over time since 1910. In most cases, extreme events
are defined as lying in the outermost (“most unusual”) ten percent of a place’s history. Analyses are available at the national and regional levels.”
National Oceanic and Atmospheric Administration
(NOAA)
92
National Oceanic and Atmospheric Administration
(NOAA)
“Climatic extremes are an important component of a location's climatology and are used for
quality controlling meteorological observations, setting engineering limits, and
helping authorities to develop climate-related safety plans, among other things.”
Emergency Preparedness for
Extreme Weather Events
93
Enhancing Emergency Preparedness(6) Enhanced Technology (esp. information management)
Common Operations
Platform for Safety (OPS)
94
Enhancing Emergency PreparednessGEO’s GInfo and EILIS (Desktop and Mobile App)
Slope information management & landslide incident reports
Concerns
95
• Landslides: serious consequences + breakdown of
existing emergency system
• Other hazards: likely to be similar situation
• Compounding effects of concurrent occurrence of
multiple hazards
• Liable to be aggravated by climate change and
continued population increase/urban development
Are we adequately prepared for extreme events ?
Based on time dependent return period analysis using non-stationery
Generalized Extreme Value (GEV) distribution model
More Frequent Extreme Rainfall in Hong Kong
ElementReturn Period
in 1900
Return Period
in 2000
1-hr rainfall > 100 mm 37 years 18 years
2-hr rainfall > 150 mm 32 years 14 years
3-hr rainfall > 200 mm 41 years 21 years
96Beware of limitations and uncertainties of downscaling studies
