The Perfect Storm - Floods devastate Manila

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The Perfect Storm: Floods Devastate Manila

A.M.F. Lagmay, R.S. Rodolfo and M.G. Bato

EARTH Vol. 55 (No. 4), p. 51

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Filipinos lift a boy onto the roof of a build-

ing to escape floodwaters brought by

Tropical Storm Ondoy in Quezon City, a

suburb of Manila, on Sept. 26, 2009.

Torrential rainfall

combines with

overpopulated

shanties in a

floodplain to

overwhelm the

capital city

of thePhilippines

THE PERFECT STORM:F l o o d s D e v a s t a t e M a n i l a

50 EARTHApril 2010 www.earthmagazine.org


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MANILA

China

Vietnam

Brunei

Taiwan

SOUTH CHINA SEA

PHILIP

CELEBESSEA

SULUSEA

Laos

Malaysia

Cambodia

Indonesia

Philippine

Bottom:AGI/NASA;top:E.deCastro

Flooding stops traffic in Cainta, Rizal, east

of Manila, Sept. 27.

Rains started pouring in the evening

of Sept. 25. By mid-afternoon the fol-lowing day in Manila, the capital ofthe Philippines, more than a monthsworth of rain had fallen. The city and

entire metro area were underwater.Some areas were flooded up to twostories high. Hundreds of peoplewere dead: drowned in their cars,their homes and in malls. The floodsbrought one of the worlds largest cit-ies to a standstill.

Although the storm devastated theManila metro area, other elements

contributed to the disaster: The entirearea is composed of a series of flood-plains with multiple large rivers run-ning through them, and the region issubsiding, faster in some parts thanothers. In addition, Metro Manila isoverpopulated, with many impover-ished residents living in shantytownsincapable of standing up to heavy rain

and floods. Add in some 44 centimetersof rain in a 12-hour period, and youhave a recipe for the perfect storm of

factors that led to the high death toll.

THE GEOGRAPHIC FACTORS

Metro Manila is locatedon an isthmus between theManila Bay, which opens tothe South China Sea, andLaguna de Bay, an approxi-mately 900-square-kilometer,2-meter-deep freshwater lakeformed partly by two volcaniceruptions. The entire region iscomposed of one major riverbasin called the MarikinaRiver Basin, which covers535 square kilometers, and

eight smaller, highly urban-ized river sub-basins, whichcover 683 square kilometers,that drain directly into ManilaBay and Laguna de Bay. TheMarikina and Pasig riversserve as the main outlet fortributaries of the MarikinaRiver Basin. Underlain bymostly volcanic and coastalsediments, the metropolis lieson one of the widest flood-

plains in the Philippines.

A.M.F. Lagmay, R.S. Rodolfo and M.G. Bato

Tropical Storm Ketsana, or Ondoy, as locals call it,

came ashore at the Philippines island of Luzon on

Sept. 26, 2009. The ensuing deluge caught everyone

by surprise.

www.earthmagazine.org EARTHApril 2010 51


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Above: Elevation map of Metro Manila and vicinities. Metro

Manila is composed of 16 cities and one municipality (yellow

outline). Orange dots are the locations of rain gauge stations.

Inset map is Luzon Island, Philippines. Left: The Marikina River

Basin (green) and sub-basins of Metro Manila. The Manila area

is composed of multiple floodplains, with several rivers draining

into Manila Bay and Laguna de Bay.

In 1986, the Manggahan floodway was built to reduce flood-ing along the banks of the Pasig River by diverting floodwa-ters into Laguna de Bay. A complementary project called theNapindan Hydraulic Control System was built at the conflu-ence of the Marikina and Pasig rivers to regulate tidal flow andprevent intrusion of polluted water into Laguna de Bay.

Despite these flood control measures, floods are still com-mon in Manila, generally occurring at least once a year duringthe rainy season. Residents have known about the regions

flood risk since at least the Spanish colonial period (1521 to1898). But usually when floods strike Metro Manila, they are

small, affecting only a few neighborhoods at a time.



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Bottomandmiddle:A.M.F.Lagmay;top:J.C.Lopez

THE STORMTropical Storm Ondoy was just one of

several storms that struck Metro Manila

last year: On average, the area is affectedby 20 typhoons each year. Ondoy was

first spotted in the Philippine Sea onSept. 24, 2009. By 11:00 p.m. local time,its center was located 611 kilometerseast of Manila moving west-northwestat 16 kilometers per hour. Following itsforecasted track, Ondoy made landfallon Sept. 26 shortly before 12:00 p.m.local time, on the eastern side of Luzon

near the border of Aurora and Quezonprovinces. The storm had maximumwinds of 85 kilometers per hour near

the center and gusts up to 100 kilometersper hour just a tropical storm, not

quite a hurricane, on the Saffir-SimpsonHurricane Scale. The slow-moving stormcrossed Central Luzon before exitingthe western seaboard toward the SouthChina Sea.

Between 8:00 a.m. and 8:00 p.m. on Sept.26, more than a months worth of rain fellon Metro Manila. The total precipitation

on Sept. 25 and 26 was 17.35 centimetersover Manila itself and 53.06 centimetersover Quezon City, northeast of down-town Manila. The regional average was44.85 centimeters of rain nearly dou-ble the 20 to 30 centimeters dumped onLouisiana by Hurricane Katrina in 2005.

Rainfall intensity was highest between11:00 a.m. and 12:00 p.m. on Sept. 26,when 9.2 centimeters of rain fell. Thewestern side of Luzon, home to Manila,received enhanced rainfall as the stormapproached because of the interactionof Ondoys circulation pattern and theseasonal southwest monsoon.

FLOODINGSome areas began flooding early in the

day. By the afternoon of Sept. 26, inun-dation ranged from ankle-high to morethan two stories high, according to anec-dotal accounts of the deluge recordedon an interactive public flood heightmap, with flow velocities as high as 15kilometers per hour along main riverchannels and their banks.

The distribution of flooding variedacross the region. Most of the high-levelfloods occurred in areas closest to riverchannels, creeks and the lake. The two

hardest-hit cities, Marikina City andPasig, for example, lie along the flood-plains of Marikina River, a major water-way that drains into Laguna de Bay.

River water rose as much as ninemeters and in many instances reachedthe base of bridge spans. Many streetsin the more than a dozen cities of MetroManila were completely submerged.

A street turns into a turbulent river in

Park 9, Katipunan, Quezon City.

Debris from a flash flood overtops a bridge

in Marikina City.

Bodies emerge in Tumana, Marikina City,

three days after the disaster as the flood

subsides.

www.earthmagazine.org EARTHApril 2010 53


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Even in places that do not normallyflood, roads were transformed into riv-ers within minutes. Such severe floodingcreated mammoth traffic jams in everycity in the metro area. In some areas, rap-

idly rising floods drowned vehicles, withinstances of passengers still in them.

Along the banks of the swollenMarikina River and its tributaries, ragingwaters swept up urban poor residents asthey stood on their shanties. Knowing no

boundaries, the floods spread into manymiddle class and upscale residential areasas well as commercial areas, drowning

people unable to climb to their rooftops intime. Grocery stores, restaurants, Internetcafs, entertainment plazas, banks, gov-ernment agencies, retail stores, hospitalsand houses were covered in mud afterthe floods receded.

At the height of the flooding, about26,000 gallons of bunker oil from a papermill in Marikina City spilled into the

water, covering several communities and

complicating rescue efforts. Ondoy alsocaused the total shutdown of electricityin the cities of Marikina, Pasig and Taguigfor days. International flights were can-celled at the Ninoy Aquino InternationalAirport for nearly 24 hours.

About 65 kilometers north of MetroManila, lahars dense, viscousmudflows poured along the south-

western slopes of the Arayat volcano,burying communities in the area.

In the aftermath of the storm, 464 peo-

ple were confirmed dead, with 37 missing

and presumed dead, and hundreds moreinjured. Nearly 27,000 houses were badlydamaged. In total, 4.73 million peoplewere affected. The top five causes of deathduring the disaster were drowning, inju-

ries, electrocution, asphyxia secondaryto landslides and heart attack due to

panic. In evacuation centers, the top fivecauses of death were acute respiratory

tract infection, skin infection/wounds,

diarrhea, febrile illness (a respiratory dis-ease) and pneumonia.

Furthermore, leptospirosis, a bacterialinfection commonly transmitted in flood-waters contaminated by the urine of ratsand other animals, killed 89 people andhospitalized an additional 1,027 people.

The number of leptospirosis cases moni-tored by the Philippines Department ofHealth has already exceeded the 800cases reported for the entire countryin 2008.

Filipinos, resilient to natural catastro-phes, have largely recovered from thedisaster. Life is back to normal in almostevery corner of the metro area. There areno traces of the devastation except for

flood marks left behind by the deluge.

Houses destroyed by flooding in Marikina

City.

Above: Mud encrusted on the wall, appli-

ances and furniture of a house in Tumana,

Marikina City. Right: Filipino citizens stand

in line for food donated by local busi-

nesses and private organizations to aid

communities affected by the storm.



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THE COMPOUNDING FACTORSThe extreme flood that devastated Metro Manila was pri-

marily due to the extremely heavy downpour on Sept. 26. Themore than 40 centimeters of rain delivered over the span of12 hours in Metro Manila is the highest period of rainfall inrecorded history. But it was compounded by geologic factors,and especially by rapid and poorly planned urbanization.

Since the 1970s, people have been migrating from ruralareas to the cities. Metro Manila has been growing signifi-cantly, increasing from 4.9 million residents in 1975 to morethan 11 million today. A survey by the National Housing

Authority showed that by the early 1980s, a quarter of MetroManila residents were informal settlers living in crowdedshantytowns with little or no infrastructure.

Furthermore, humans have altered the landscape in thisregion. A variety of factors contributed to the generation ofmassive floods, including encroachment of concrete surfaces,densification of buildings and residential areas, silting ofriverbeds and canals, obstruction of waterways by informalsettlers, clogging of floodways by garbage, narrowing of riv-

ers due to development on floodplains, draining and filling in

of small rivers forcing more water into fewer channels, forestdegradation, and reclamation of coastal land.

Further complicating the problem is ground subsidence.From 1978 to 2000, parts of Metro Manila sank by an amountranging from 16 centimeters to 1.46 meters. The probablecauses of subsidence are excessive groundwater extrac-tion, soil compaction and tectonic movement, though moreresearch is needed to fully determine the primary causes.

In the end, the flooding from this storm was a catastropheof unimaginable proportions. It was a natural hazard, com-pounded by human actions, making it a natural disaster.The attention brought by Ondoy, hopefully, can focus future

efforts to address the growing concern of worsening floodscomplicated by uncontrolled urbanization in the capital ofthe Philippines.

All three authors are geologists at the National Institute of

Geological Sciences at the University of the Philippines in

Quezon City.

B

ottomright:A.M.F.Lagmay;top:

iStockphoto.com

/HectorJosephLumang

The population of Metro Manila has boomed in the last couple of

decades, with tens of thousands of people living in shanties likethese, many of which were demolished by the storm.

Aerial photograph of shantytowns constricting

the Manggahan floodway, a major artery meant

to ease floods during rainstorms.

www earthmagazine org EARTH April 2010 55

The Perfect Storm - Floods devastate Manila

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