Ondoy Tragedy
Lessons to be learned…
Fernando Siringan
ando.msi@gmail.com
Marine Science Institute, University of the Philippines Diliman
Gemma Narisma, Rosa Perez, Celine Vicente, Antonia
Loyzaga
Manila Observatory
Mahar Lagmay
National Institute of Geological Sciences, University of the Philippines Diliman
http://earthobservatory.nasa.gov
Observations from TRMM from
Sept 21 to 27, 2009
70
Rain
1005
60
Barometric Pressure
Wind Direction
and Wind Speed
1000
50
40
995
30
20
990
Pressure (hPa)
Rain (mm)
Hourly Rainfal, Average Pressure and Winds
in Manila Observatory (26 Sep 2009)
10
0
985
12 AM
3 AM
6 AM
9 AM
12 PM
3 PM
6 PM
9 PM
Time (pht)
•
•
The highest rainfall was measured in Manila Observatory between 9 AM and 1 PM.
Highest rainfall of 61.4 mm/hr was measured at 10 AM
Accumulated Rainfall in Manila Observatory
(21-28 Sep 2009)
500
Weekly Accumulated Rain = 459.8 mm
Accumulated Rain
Daily Rain (mm)
400
Daily Rain
26 Sep 2009
368.6 mm
Daily
Normal Monthly Accumulated Rain for September
300
200
100
0
9/21
9/22
9/23
9/24
9/25
9/26
9/27
9/28
•
“Ondoy” brought a total of 368.8 mm of rain over Manila Observatory on
September 26, 2009.
•
This daily rain measured in Manila Observatory is higher than the monthly
normal (330.3mm) in the Port Area.
Rain Accumulated in Southern and Central Luzon (21-28 Sep 2009)
330.3
mm
http://www.nscb.gov.ph/headlines/StatsSp
eak/2009/030909_rav_climatechange.asp
http://trmm.gsfc.nasa.gov/trmm_rain/Events/manila_rainfall_perspective_21-28sep09.jpg
Accumulated rainfall over a week measured
by TRMM was over 500 mm in Metro
Manila. This value is higher than the monthly normal.
Ondoy is an extreme event.
But is Ondoy a manifestation of climate change?
350
300
1/1/1961
1/1/1962
1/1/1963
1/1/1964
1/1/1965
1/1/1966
1/1/1967
1/1/1968
1/1/1969
1/1/1970
1/1/1971
1/1/1972
1/1/1973
1/1/1974
1/1/1975
1/1/1976
1/1/1977
1/1/1978
1/1/1979
1/1/1980
1/1/1981
1/1/1982
1/1/1983
1/1/1984
1/1/1985
1/1/1986
1/1/1987
1/1/1988
1/1/1989
1/1/1990
1/1/1991
1/1/1992
1/1/1993
1/1/1994
1/1/1995
1/1/1996
1/1/1997
1/1/1998
1/1/1999
1/1/2000
1/1/2001
1/1/2002
1/1/2003
1/1/2004
Rainfall (mm)
400
334.5
276.5
250
403.1
265.4
223
371.4
257.4
Daily rainfall at Science Garden
(1961-2004) 267
246.4
200
150
100
50
0
Date
Daily rainfall at Port Area
(1961-2004)
252.8
Essential parts of a warning system …
Since rainfall is highly variable even over a small
area, it is best to have a good network of weather
stations – data can be viewed by anybody through
the internet.
A similar network of river gages – also viewable
through the internet.
Water level of dams can be included in the
network.
What is causing our worsening floods?
River channel capacities are decreased by…
Encroaching houses
and fishponds
Increased siltation due
to deforestation


Garbage
Fishpond encroachment (from DPWH)
Sta.
7+000
Guagua River
Malusac River
In Metro Manila worsening floods are
typically attributed to insufficient drainage …
drainage structures are outdated relative to
degree of urbanization … some are century old
channel capacities decreased by…
encroachment of structures …
filling up of river channels … by sediments
and garbage
disappearance of about 21 km of small
rivers (Zoleta-Nantes, 2000) – converted for
housing or other uses by government and private
entities
Climate change?
River
Longos area
Where is the river?
Missing river?
Other causes of
worsening floods
Decrease in
floodplain area

Urban sprawl
Flood control dikes


Fishponds
Global sea level rise

Land subsidence. The
least understood, but
very important.
Land subsidence
Lowering of land, even
large areas, due to:
Natural compaction of
underlying soil and sediment

Compaction sped up by
rapid withdrawal of
groundwater
Long-lasting floods
that now last for
months occur in…
coastal CAMANAVA
and the PaterosTaguig-Muntinlupa
area where floods are
due to elevated lake
levels during the rainy
season
But in CAMANAVA,
floods can be caused
by high tide alone…
but this was not so in
the past.
At Manila’s South Harbor mean sea level rose
at about 2 millimeters per year from 1902 to
the early 1960’s. . .
. then started rising ten times as fast. WHY?
Groundwater withdrawal!
778 MLD
250
MLD
<20 million liters
per day (MLD)
1770 MLD in 2004
(CEST 2004)
989 MLD in 1990
(JICA 1992)
Metro
Manila`s
groundwat
er demand
is still
increasing.
Consequent
subsidence
will continue
and may
even
accelerate !
How groundwater withdrawal causes land to subside
Pumps extract water from
“aquifers” –layers of sand
and gravel soaked with
water.
If too much water is
pumped out of the aquifer,
the pressure is reduced in
the pore spaces between
grains of sand and gravel.
Pipe appears
to rise out of
the ground
Water in the clay layers is
sucked into the aquifer.
This causes the clay
layers to shrink . . .
We need to lessen our dependence on
groundwater.
. . . and the ground
surface to sink.
Benchmarks used for releveling (1978 vs 2000)
survey (Jacob 2004)
Tuff
1.40
1.46
0.76
Maximum magnitude of
subsidence – 1.46 m (6.1 cm/y)
0.79
0.16
0.88
0.96
0.77 0.95
0.95
0.64
0.96
0.73
0.67
Coastal/Alluvial
0.57
0.59
0.61
0.51
0.57
0.46
0.43
0.46
0.47
0.46
Change in height of maximum
high tide, from 1991 to 2002
based on social survey ranges
from 0.5 - 1.0 m (4.5 – 9.1 cm/y)
There appears to be an
acceleration in rate of
subsidence in recent years.
Lateral variation in magnitude
of subsidence is not a function
of underlying lithology.
Piezometric Surface
2004 (CEST, 2004)
GUIGUINTO
1640000
STA. MARIA
BALAGTAS
CITY OF SAN JOSE DEL MONTE
ROD
BULACAN
BOCAUE
MARILAO
1630000
MEYCAUYAN CALOOCAN CITY
OBANDO
VALENZUELA
CITY OF MALABON
QUEZON CITY
1620000
NAVOTAS
SAN MATEO
-120
CALOOCAN CITY
CITY OF
-40
CITY OF MARIKINA
0
-20
-40
CITY OF MANILA SAN JUAN
1610000
CAINTA
MANILA BAY
MANDALUYONG
PASIG
PASAY CITY
MAKATI
PATEROS
TER
TAYTAY
ANGONO
TAGUIG
BINAGONAN
1600000
CAVITE CITY
KAWIT
CITY OF PARANAQUE
CITY OF LAS PINAS
NOVELETA
BACOOR
IMUS
1590000
Piezometric Level
1951 (NHRC, 1991)
MALOLOS
CITY OF MUNTINLUPA
LAGUNA LAKE
Trace of West
Marikina Valley Fault
M 6-7 earthquakes
recur every 200 to
400 years (Nelson et
al., 2000) and have an
associated ~0.5 m
vertical displacement
(R. Rimando pers.
comm.)
(Sources: 1:50,000 topographic maps of Namria, 1990 and 1992)
Subsidence along the
Marikina Valley can be
due to combined
natural, earthquake
and human induced
compaction.
Other SE Asian sites experiencing subsidence
due to over extraction of groundwater
LOCATION PERIOD
SUBSIDENCE
Meters cm/year
Tokyo,
Japan
1918-87
4.5
6.5
Osaka,
Japan
1934-68
2.8
8.2
Shanghai,
China
1921-65
2.63
6
Shanghai
Yun-Lin
Yun-Lin,
1989-97
0.66
8.25
Hanoi
Taiwan (Fishpond area!)
Manila
Hanoi,
1988-93 0.1-0.3
2-6
Vietnam
Bangkok
CAMANAVA 1991-2002 0.3 - 1 2.7 – 9.1
Bangkok, 1980-90
Thailand
Jakarta, 1991-99
Indonesia
0.5-1
5-10
0.3-0.8
4-10
Jakarta
Tokyo
Osaka
121°30' E
121°00' E
121°15' E
121°30' E
14°30' N
14°15' N
14°15' N
14°30' N
14°45' N
121°15' E
14°45' N
121°00' E
Bathymetric data based on
1920 to 1939 hydrographic
surveys
Bathymetric data based on
1997 to 1998 hydrographic
surveys
1
1
1
2
2
2
1
2
3
3
3
4
4
3
1
2
4
3
3
4
4
1
2
1
2
3
3
4
1
2
3
3
4
3
1
0
5
10
3 2
2
15 Km
contour interval 0.5m
3
1
0 5 10 15 Km
contour interval 0.5m
0
5
10
3 2
2
15 Km
contour interval 0.5m
Lake surface area
922 km2
Lake surface area
869 km2
Total lake volume
2.32 x 109 m3
Total lake volume
1.95 x 109 m3
Average water
depth
2.52 m
Average water
depth
2.24 m
Change in Bathymetry (1939 to 1968)
Change in Bathymetry (1968 to 1998)
The
Manggahan
Floodway
is a major
source of
sediment.
Immediate and long-term solutions to Laguna de
Bay inundation …
Increase the number of channels draining the lake - widen
Taguig River and revive other rivers in Taguig Delta Plain.
For the long-term, modification of Napindan structure might
be required.
Increase the capacity of Pasig River through channel
widening – remove major constrictions.
… a shallow but wide channel is more efficient than a deep
but narrow channel because the gradient is almost flat.
… allow planned, episodic high discharges to flush
accumulated sediment and other debris within the channel.
Control erosion in the watersheds and sedimentation in
Laguna de Bay. We need a good forest cover.
The Ondoy tragedy is due to an extreme event …
But …..
Magnitude and extent could have been much less
Given wider and deeper channel ways
Greater capacities of natural retention ponds
For the future,
among others we should increase, widen and
deepen our channel ways,
implement easement rules,
reforest, allocate retention ponds
Houses on stilt in
Candaba
FLOOD HEIGHT: 4-5m
Photo by J. Ong
4
Pacific Decadal Oscillation
Standard Departure
3
2
1
0
-1
-2
-3
-4
Standard Departure
3
Multivariate ENSO Index
2
1
0
-1
-2
-3
1900
1910
1920
1930
1940
1950
1960
YEAR
1970
1980
1990
2000