Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines, December 2012

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Chapter
Super Typhoon Bopha and the
Mayo River Debris-Flow Disaster,
Mindanao, Philippines, December
2012
Kelvin S.Rodolfo, A.Mahar F.Lagmay, Rodrigo C.Eco,
Tatum Miko L.Herrero, Jerico E.Mendoza, Likha G.Minimo,
Joy T.Santiago, JenalynAlconis-Ayco, Eric C.Colmenares,
Jasmine J.Sabado and Ryanne WayneSerrado
Abstract
Category 5 (C5) Super Typhoon Bopha, the world’s worst storm of 2012, formed
abnormally close to the West Pacific Equator, and Bopha’s Mindanao landfall has
the record equatorial proximity for C5 storms. Bopha generated a debris flow that
buried 500 ha of New Bataan municipality and killed 566 people. New Bataan,
established in 1968, had never experienced super typhoons and debris flows. We
describe the respective histories of New Bataan and Super Typhoon Bopha; debris
flows; and how population growth and unwise settlement practices contribute to
Philippine “natural” disasters. The historical record of Mindanao tropical cyclones
yields clues regarding how climate change may be exacerbating near-equatorial
vulnerability to typhoons. Existing models of future typhoon behavior do not apply
well to Mindanao because they evaluate only the tropical cyclones that occur during
the main June–October typhoon season, and most Mindanao tropical cyclones
occur in the off season. The models also ignore tropical depressions, the most
frequent—and commonly lethal—Mindanao cyclones. Including these in annual
tallies of Mindanao cyclones up to early 2018 reveals a pronounced and accelerating
increase since 1990. Mindanao is susceptible to other natural hazards, including
other consequences of climate change and volcanic activity.
Keywords: Super Typhoon Bopha, Andap disaster, Mayo River, debris flows,
climate change, ENSO, typhoon frequency
. Introduction
On 4 November, 2012, Super Typhoon Bopha generated a massive debris flow
that devastated barangay (village) Andap in the Mindanao municipality of New
Bataan and killed hundreds of people. In early 2013, we were designated as a field
disaster-analysis team by Project NOAH (Nationwide Operational Assessment of

Meteorological Hazards, Climate Change and Super Storms

Hazards), the disaster-assessment program of the University of the Philippines in
Diliman, Quezon City.
Prior to our field work, we gathered high-resolution optical satellite imagery
for mapping out the extent of the debris flow deposits and commissioned a Light
Detection and Ranging (LiDAR) survey to generate detailed topographic maps of
the area. In the field, we analyzed and plotted the new deposits on our new maps.
They were clearly left by a debris flow, and we determined its velocity when it
hit Andap from scarring on impacted trees. Old deposits were left in the area by
debris flows that occurred long before New Bataan was established. Eyewitnesses
recounted the Bopha event for us in detail, and long-time residents informed us
that similar events had never happened before. We analyzed and reconstructed the
event from all these gathered data.
An initial report we published in 2016 [1] described the Super Typhoon, the
Mayo River debris flow, and the detailed geologic reasons for it. We also discussed
how and reviewed how population growth and inadequate geological analysis of
settlement sites contribute to Philippine “natural” disasters. Our report discussed
how climate change may be bringing more frequent major typhoons and debris
flows they trigger to Mindanao and to other vulnerable subequatorial areas. We
did so by examining the sparse record of tropical cyclones that made landfall on
Mindanao since 1945, associated records of the Pacific El Niño-Southern Oscillation
(ENSO), and all western North Pacific tropical cyclones from 1945 to 2015.
Here, we update that evaluation with additional data from 2016 through
February 2018. A positive outgrowth of this research is Project NOAH’s new pro-
gram that has identified more than a thousand Philippine alluvial fans and associ-
ated communities that might experience debris flows. This program already helped
to mitigate debris flows on Luzon and Mindoro islands. We conclude by exploring
possible protective measures for climate-related hazards that threaten Mindanao
and other subequatorial areas.
. Prolog to disaster: geomorphologic setting and history of New Bataan
Southeastern Mindanao is a rugged coastal range (Figure ). About 35km
west of the coast, and 3km upstream of Andap, the Mayo River drains a rugged,
36.5km2 watershed on the western slopes of the coastal range. In the Mayo water-
shed, many slopes are steeper than 35° and total relief is about 2320m. Flowing
northward, the Mayo River debouches through a narrow gorge to join the Kalyawan
River, which flows northward along the Compostela Valley, as do other Agusan
River southern tributaries.
A site 8km below the Mayo-Kalyawan junction in the eastern Compostela Valley
called “Cabinuangan” because of its many huge Binuang (Octomeles sumatrana)
trees began to be logged in the early 1950s [2]. As the loggers rapidly expanded their
road networks, immigrant farmers from Luzon and the Visayan Islands followed
closely behind, planting the cleared land mainly to coconuts, but also to rice, corn,
bananas, coffee, cacao, abaca, and bamboo.
The Philippine government divided the public lands of Compostela Valley into
formal municipal areas beginning in 1966. One covering 55,315ha in Cabinuangan
was named New Bataan in 1968 because Luz Banzon-Magsaysay, a native of the
Luzon province of Bataan and President Magsaysay’s widow, had espoused its
establishment. New Bataan was subdivided into 16 barangays (villages) comprising
farm lots. A 154-ha area at the center of New Bataan was designated the town site
and given the barangay name of “Cabinuangan.” In 1970, 2 years after its founding,

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Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
DOI: http://dx.doi.org/10.5772/intechopen.81669
the population of New Bataan was 19,978 [3]; by 1 May, 2010, it had increased 238%
to 47,470, including 10,390in Cabinuangan and 7550in Andap [4].
The town planners made a nice design for Cabinuangan, its streets fanning out
geometrically from its central core of government and social buildings (Figure A).
Unfortunately, the planners knew little about natural hazards. Even government
authorities did not know that the Kalyawan River had been a conduit for ancient
debris flows; as late as 2012, the official hazard map of New Bataan [5] evaluated
only landslide and flood risks. This lack of geomorphologic knowledge was fatal
during Bopha (Figure B).
Barangay Andap was established at the head of Compostela Valley on high
ground 3km upstream of Cabinuangan. That site was not recognized as an alluvial
fan, a landform built up by successive debris flows. Our field work documented that
the fan was built up by characteristically reverse-graded, matrix-supported debris-
flow deposits of unknown but ancient age (Figure ).
Figure 1.
Physical setting of the Andap disaster. Gray area enclosed by dashes is the Mayo River watershed. All
steep slopes are contoured at 50-m intervals. Below 700-m elevations, the contour interval is 20m to better
define the gentler valley surfaces. New deposits of “true” debris flows are shown in solid black; associated
hyperconcentrated-flow deposits are shaded in gray. Note that the topographic contour lines from the Mayo
Bridge to Andap are convex northward, defining the surface of an alluvial fan just upstream from Andap. The
trace of the Mati Fault is only generalized; it has numerous associated fractures in a broad zone along its length.

Meteorological Hazards, Climate Change and Super Storms

. Debris flows
Among the world’s most destructive natural phenomena, debris flows are
fast-moving slurries of water and rock fragments, soil, and mud [6–9]. Many debris
flows (Table ) [10] are associated with volcanoes [11, 12]; many others are not,
including the Mayo River event. All that is required to generate a debris flow is an
abundance of loose rock debris and soil and a sudden large influx of water. They
Figure 3.
Debris-flow deposits in the New Bataan area. (A) Boulder in ancient reverse-graded debris-flow deposit.
Well-established trees indicate an age of some decades prior to the settlement of the town. (B) Old debris-flow
deposits underlying New Bataan—Andap high-way. Boulders and cobbles are separated from each other by
a matrix of finer-grained sediment, as they were while still flowing. For scale, the concrete is 15-cm thick.
The coarse sediments atop the highway are new debris-flow deposits from Typhoon Bopha. (C) Boulder-rich
deposits of debris flows that destroyed much of the barangay, at the site of the destroyed Mayo River bridge.
Figure 2.
New Bataan. A= Andap, Google image of Cabinuangan (the central district of New Bataan) before the debris
flow. B= Southward facing three-dimensional terrain diagram of Andap and Cabinuanga after the Mayo River
disaster. Red areas are boulder-rich “true debris flow; orange areas are deposits of more dilute “ hyperconcentrated”
flows.

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Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
DOI: http://dx.doi.org/10.5772/intechopen.81669
can be triggered by sudden downpours such as commonly delivered by tropical
cyclones, by reservoir collapses [13], or by landslides dislodged by earthquakes into
streams.
The lethality and capacity for damage of a debris flow is not determined by its
size alone. If its path is sparsely populated, such as at Mount St. Helens, or if the
people in harm’s way are familiar with the hazard, such as at Pinatubo Volcano, even
large debris flows may not inflict casualties.
Rain on mountain slopes that falls strongly and lasts long enough will dislodge
soil and loose rock into landslides. These may coalesce into debris flows, which are
slurries of sediment and water that look and behave like concrete pouring out of a
delivery truck. By weight, the water rarely exceeds 25%; only 10% may be enough to
provide mobility. Gravel and boulders constitute more than half of the solids, and
sand typically makes up about 40%. Silt and clay normally constitute less than 10%
and remain suspended in the water [21, 22]. Students of debris flows frequently
say “In stream floods, the water carries the sediment; in debris flows, the sediment
carries the water.”
While a debris flow is contained in a mountain channel, it carries large boul-
ders with remarkable ease. In part, this is because of the high buoyancy of the
dense slurry. Additionally, boulders in the flow repeatedly bounce away from the
channel floor and sides up into the “central plug” of the flow near the surface,
where friction with the channel is minimal and the flow is fastest, enabling them
to migrate quickly to the front of the flow. There, they become part of a moving
dam of boulders, logs, and tree debris being pushed along by the flowing mass
contained behind it.
Location Date Trigger Volu me,  mDeaths
Rios Barrancas and Colorado,
Argentina [14]
1914 Failure of ancient
landslide dam
2000 estimated ?
Bucao River, Pinatubo Volcano,
Philippines [13]
10 July,
2002
Caldera lake breach <<160 0
Bucao River, Pinatubo Volcano,
Philippines [15]
5–6
Oct,
1993
Typhoon Flo
(Kadiang) rains
110 0
Kolka Glacier, North Ossetia,
Russia [16]
2002 Large glacial
detachment
~100 125
Nevados Huarascan, Peru [17]1970 Pyroclastic flows
melted snow and ice
100 (flow
volume)
18,000
Nevado del Ruiz, Colombia [14]13 Nov,
1985
Pyroclastic flows
melted snow and ice
40 23,000
Mayo River, Mindanao,
Philippines [1]
4 Dec,
2012
Typhoon Bopha
(Pablo) rainfall
25–30 566
Cordillera de la Costa, Vargas,
Valenzuela [18]
Dec
1999
Heavy rain 19 30,000
Mayon Volcano, Philippines [19]30
No v,
2006
Typhoon Durian
(Reming) rains
19 1226
Pine Creek—Muddy River, Mount
St. Helens, Washington, USA [20]
18
May,
1980
Pyroclastic surge
melted snow & ice
14 0
Table 1.
The global record of the 10 largest debris flows, ranked by decreasing volume. Modified and updated from [].

Meteorological Hazards, Climate Change and Super Storms

The moving frontal dam ponds the main flow body, which is richer in sand, silt,
and clay and progressively becomes more dilute toward the rear, undergoing transi-
tions into what are called hyperconcentrated flows, somewhat confusingly because
they carry much more sediment than do normal streams. In hyperconcentrated
flows, sand, silt, and clay typically comprise up to 75% by weight. Such flows look
like normal, turbid flood waters, but their velocities are much greater, typically
2–3m/s [23]. They are too dilute to transport boulders and can transport gravel
only by pushing and rolling it on the channel floor. To the rear, hyperconcentrated
flows are succeeded by even more dilute, turbid flood water. In the literature,
somewhat confusingly, “debris flow” sometimes refers to only a true debris-flow
phase. Sometimes, however, the term means an entire hydrologic event consisting
of debris-flow, hyperconcentrated, and normal stream-flow phases, as we do here
in reference to the Mayo River debris flow.
When a debris flow emerges from the mountains, it spreads out, and the
increased basal friction slows it down. Some of its sediment load drops out and adds
volume to an alluvial fan, a cone-shaped feature that topographic maps show as
contour lines that are convex in the downstream direction, as seen in Figure . Even
after the debris flow spreads out, large boulders (Figure ) continue to be trans-
ported by combined flotation, push, drag, and rolling. The hyperconcentrated and
normal-flood phases may extend many kilometers beyond the alluvial fan. Debris
flows vary in volume by many orders of magnitude (Table ), the most frequent
ones being only a 1000–100,000m3 and the largest more than a 100,000,000m3
[10].
An important distinguishing characteristic of true debris-flow deposits is
“reverse grading”: boulders tend to be smaller at the base and increase in size
upwards. Large boulders commonly jut out at the top of a deposit, as observed at
New Bataan (Figure A). In addition to the buoyancy they experience from the
dense slurry, the best mechanism advanced to explain reverse grading is kinetic
sieving [7, 11, 24–26]. While flowing, shear at the base of a debris flow continuously
causes temporary void spaces of different sizes to open, and particles of equivalent
sizes migrate into them. Smaller voids form and are filled by smaller solid particles
more frequently, and so larger boulders migrate up toward the top of the flow.
Another characteristic of debris-flow deposits that distinguish them from the
deposits left by normal streams, in which particles grade upward from coarse to
fine, is “matrix support” (Figure B). A mixture of the finer sediment that consti-
tuted the bulk of the flow separates the larger rock fragments from each other. A
useful guide for distinguishing the effects of debris flows from those of floods was
published by Pierson [27].
. Super Typhoon Bopha
On 23 November, 2012, a large area of convection began forming at 0.6°N
latitude, 158°E longitude [28] (Figure A). Two days later, while still unusually
close to the equator at 03.6°N, 157°E, it was categorized as a tropical depression. It
was upgraded to Tropical Storm Bopha three days later on 26 November, while at
04.4°N, 155.8°E, a latitude where the Coriolis effect was too weak to quickly cause
it to rotate. Only four days later, on 30 November, while Bopha was still at 3.8°N,
145.2°E, it did grow into a Category 1 typhoon.
Bopha then rapidly gained in intensity. On 1 December, while at 5.8°N, 138.8°E, it
had intensified into a C4 Super Typhoon. On 2 December, wind speeds were 259km/h,
those of a C5 Super Typhoon. Notably, this happened while Bopha was at 7.4°N,
128.9°E, closer to the equator than any Category 5 tropical cyclone ever had before. On

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Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
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3 December, as Bopha interacted with Palau Island, it weakened temporarily into a C3
typhoon before reintensifying back to C5. On 2 December, Bopha entered the Philippine
area of responsibility at 8a.m. local time and was assigned the local name of Pablo.
Bopha crossed the eastern Mindanao coast at about 7.7°N on 4 December at
0445H, the global record proximity to the equator for all C5 tropical cyclones
(Figure B). Average wind speeds and gusts were 185 and 210km/h, respectively.
Many fisher folk at sea were lost, and many coastal dwellers were drowned.
Once onshore, Bopha weakened rapidly as it expended much of its energy in
wreaking great havoc. Numerous deaths and severe injuries were attributed to fly-
ing trees and debris [29]; however, by far, the greatest cause of death and destruc-
tion was the Mayo River debris flow that the typhoon rains generated (Figure C).
Bopha passed through Mindanao, entered the Sulu Sea, and crossed Palawan
Island to enter the West Philippine Sea. There, it reversed course and approached
northern Luzon but dissipated before reaching it.
The United Nations Office for the Coordination of Humanitarian Affairs
(UNOCHA) [30] reported that 1146 Filipinos were killed by Bopha; 834 were still
missing, and 925,412 were rendered homeless. It totally or partially destroyed more
than 233,000 and caused 1.04 billion U.S. dollars of damage to buildings, crops,
and infrastructure. Bopha was the most costly typhoon in Philippine history up
to that time—only to be superseded less than a year later in November 2013 when
Super Typhoon Haiyan generated the storm-surge that destroyed Tacloban City and
devastated widespread areas in the central Philippines.
Figure 4.
Typhoon Bopha (Pablo). (A) Track and development of the Super Typhoon. New Bataan, Andap, and the
Maragusan rain gauge lie beneath the Category 3 icon following the Mindanao landfall. (B) Bopha nearing
landfall (modified from [28]). (C) Tropical Rainfall Measurement Mission (TRMM) image from which
NASA [28] estimated that Bopha delivered over 240mm of rainfall near the coast.

Meteorological Hazards, Climate Change and Super Storms

. The Mayo River debris flow
The available rain gauge data for Bopha were gathered at Maragusan munici-
pality, 17km south of Andap (Figure ). Even at that distance, given the Bopha’s
huge size, these data are good proxies for the rainfall that caused the debris flow.
They show that the Mayo River watershed received 120mm of rain from midnight
on 4 December until the flow occurred at 6:30 that morning. It fell as intensely as
43mm/h, and 4.4 million m3 were accumulated. These values greatly exceeded the
debris-flow initiation thresholds at the Philippine volcanoes Mayon and Pinatubo
[31, 32] and Taiwan [33, 34].
After the debris flow began, it was sustained by another 24mm of torrential rain
that fell until 7a.m., delivering an additional 900,000m3 of water. The rainstorm
peak in intensity, 52mm/h, happened at 6:45a.m. A half-kilometer downstream of
the Mayo Bridge (Figure ), the Mamada River discharges into the Kalyawan River;
the storm runoff from its 17.7km2 watershed, along with the discharge from other
Kalyawan tributaries, diluted the debris flow into hyperconcentrated flows that
extended 2km beyond Cabinuangan (Figure B).
Several geological factors contributed to make the debris flow possible. The Mati
Fault in Figure  is a major splay of the Philippine Fault zone, so the rocks of the Mayo
watershed have undergone extensive fracturing, making abundant rock debris and
facilitating its weathering into soils. Mining and logging has denuded the watershed
slopes, facilitating landslides. Bopha’s winds uprooted trees on the slopes, exposing
soils to storm runoff. Soils are rich in clay, which increases the debris-flow mobility and
runout distance [35]. Furthermore, the 2012 debris flow swelled as it easily incorpo-
rated the old debris-flow deposits that lay abundantly along its path (Figure B).
At about 6:30a.m., Andap resident Eva Penserga watched in horror as a sturdy
concrete bridge 1.5km upstream of Andap was obliterated by the 16-m high front of
a full-fledged debris flow emerging from the Mayo River gorge. A truck on the bridge
Figure 5.
The rainfall that triggered and sustained the Mayo debris flow. Histogram measures the rain that fell during
successive 15-minute intervals; 120mm had accumulated by the time the debris flow hit Andap. Another
24mm of peak rainfall sustained the flow until 0700H before the storm began to wane.

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Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
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carrying 30 construction workers was carried away. Several minutes later, surviving
Andap residents watched for 5–10 minutes as the debris flow passed through the village.
Tragically, alerts radioed by the government before the catastrophe had urged
people to avoid floods at the Andap community center because it stood on high
ground. About 200 of them joined the local inhabitants there; 566 people were
swept away, 7.5% of the population counted in Andap by the 2010 census.
We calculated a maximum debris-flow velocity of 60km/h from amateur videos
and the length of the debris-flow deposit. Nothing could withstand the main flow,
but along its eastern edge, 70m upstream from the obliterated Andap community
center, slower velocities are documented by damage to trees that still survived
(Figure ). When a flow of water or debris encounters and rides up an obstruc-
tion, the height to which it rises is a measure of its velocity [36]. If all of the kinetic
energy of the flow was converted to potential energy as it rose up against the trees,
the 1.8m run-up height h recorded by the highest damage indicates a velocity v of
5.8m/s, or 21km/h, from v=(2gh)1/2. This is only a minimal value, because the
formula takes neither channel roughness nor internal friction into account.
Our satellite imagery, the maps of Bopha after the disaster that we made with
LiDAR data, and our field measurements yield a volume of the Andap debris-flow
deposit of 25–30 million m3. This ranks it seventh among the largest debris flows of
the world (Table ). The width of the deposit is 0.2–1km wide. The deposits with
the greatest thickness of 9m, in the 500ha Andap area, includes boulders 16m
in size (Figure C). Thicknesses decrease downstream to about 0.25m, and the
sediments diminish in size into pebbly, laminated hyperconcentrated-flow sands
that cover a 2000ha area which extends 8km north of Cabinuangan. In this area,
abundant tree trunks and other forest debris (Figure ) that contained many cadav-
ers accumulated in creeks. To impart a sense of the maximal damage, the debris
flow wreaked upstream of Cabinuangan, and Figure  presents before and after
aerial coverage of the Mayo Bridge and Andap areas.
Figure 6.
Data used to reconstruct the velocity of the debris flow that destroyed Andap. The woman is pointing at the
flow level before run-up. Remnants of Andap are in the background; the yellow sign commemorates all the
victims by name.

Meteorological Hazards, Climate Change and Super Storms

Figure 8.
Upstream impacts of the debris flow. (A) Google image of the Mayo River and Mayo Bridge before the debris
flow. (B) Post-Bopha air photo of the same area. The large boulder in Figure 3C is where the temporary road
crosses the stream. (C) Air photo of Andap before Bopha. (D) Same area after the debris flow.
. The role of Philippine population growth
The global increase in death and damage from natural calamities can be ascribed
in part to anthropogenic climate change, but another important reason is the
expansion of growing populations into high-risk areas [37]. Landslide disasters are
also increasing in developed European and North American nations [35–39], but
the trend is especially pronounced in places visited by tropical cyclones [40, 41].
Nowhere is this better exemplified than in Mindanao and by the Andap catastrophe.
The founding of the newer Mindanao settlements including New Bataan was
largely driven by rapid population growth [42]. In 1950, the average Filipino
farmer cultivated one hectare; this was cut in half by the early 1980s. When New
Bataan was settled in 1968, the Philippine population was 36.4 million and was
growing 2.98% a year. By July 2018, it had almost tripled, to 106.6 million [43]. A
congressional bill filed in 2003 was meant to provide contraception to the poor. The
Philippines is predominantly Roman Catholic, and only after strenuous clerical
opposition was the bill finally passed in December 2012—coincidentally, the month
that Bopha arrived. It must be said that, for all his failings, Rodrigo Duterte is the
Figure7.
Hyperconcentrated flows left large tangles of lumber and tree debris with many cadavers at numerous
Cabinuangan (central New Bataan) sites.

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Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
DOI: http://dx.doi.org/10.5772/intechopen.81669
first Philippine President to take population growth seriously, beginning with his
providing contraception to the poor of Davao City when he was its Mayor. Still,
the annual growth rate has dropped to 1.72%, but that equates to two million more
Filipinos annually. Virtually no areas free of hazards are available to house them.
The Philippine coastal areas, which provide housing and sustenance for two-thirds
of the population, are fully developed and increasingly crowded. Metro Manila, the
most populated and fastest-growing area, is extracting so much that it is subsiding
several centimeters to more than a decimeter annually, losing area to the sea and
becoming ever less able to accommodate more people because of worsening floods and
tidal incursions [44]. Other rapidly growing Philippine coastal cities including Davao
City southwest of Andap (Figure B) are probably experiencing the same problems.
Real-estate interests are taking advantage of the urgent need for living space by
seeking to reclaim 38,272 ha of Philippine coastal areas, including 26,234 ha that
comprise virtually the entire near-shore zone of Manila Bay [45]. This, even though
rapid subsidence increasingly subjects coastal Metro Manila to storm surges, and the
metropolis is overdue for a major earthquake, enhanced ground shaking and liquefac-
tion that would disproportionately damage reclaimed land. Inexorably, other people
are seeking living space inland, where natural hazards abound, especially landslides
and debris flows. Davao City is a 100-km southwest of Andap (Figure B). Before
leaving to assume the Presidency, Mayor Rodrigo Duterte approved a 200-ha reclama-
tion project for the city [46]. No geological feasibility studies were conducted. The
city shares a similar geographic setting with Tacloban City, at the head of a bay. In
2013, a huge storm surge generated by Typhoon Haiyan was funneled up the bay to
obliterate much of Tacloban. Davao City is close to segments of the Philippine Fault;
offshore earthquakes could similarly funnel tsunamis up to Davao.
. Will climate change bring more frequent typhoons to Mindanao?
. The historical record of tropical cyclone landfalls in Mindanao
The alluvial fan on which Andap was built, and the ancient debris-flow depos-
its under New Bataan testify that such flows occurred many times before Super
Typhoon Bopha. The youngest of these left the deposits underlying the highway in
Figure B; the sizes of some trees rooted in old deposits (Figure A) indicate that
one event occurred decades or even a century before New Bataan was settled in 1968.
Do these old debris-flow deposits and the Andap disaster merely represent the most
recent rare and essentially random Super Typhoons, or will Mindanao and other low-
latitude regions suffer from such catastrophes more frequently as the climate changes?
Most climatologists [47–52] equate climate change with fewer but more intense tropical
cyclones due to rising sea-surface temperatures and atmospheric water vapor. But this
says nothing about whether typhoons will hit Mindanao more frequently in the future,
even though their history since 1945 suggests as much (Figure A).
The literature regarding the frequency of West Pacific typhoons yields little
insight pertinent to Mindanao. Two reports [53, 54] exemplify the problem; the
significant multi-year fluctuations they reported are not manifested in Mindanao.
Neither study included tropical depressions among their data because these are
harder to define and are more ephemeral, and thus they ignored most of the
Mindanao occurrences. Landfalls are easy to locate; however, tropical depres-
sions can be lethal on Mindanao. For example, 5 of the 13 that came after Bopha
(Figure A insert) caused fatalities. In addition to ignoring tropical depressions,
the data set utilized by reference [54], which is entitled “Inactive Period of
Western North Pacific Tropical Cyclone Activity in 1998 –2011,” was limited to

Meteorological Hazards, Climate Change and Super Storms

tropical cyclones of the June -October main typhoon season. Of the 45 that made
landfall on Mindanao since 1945, only 5 came in that season: Typhoons Kate in
October 1970 and Ike in September 1984, and 3 of the 11 tropical depressions. For
Mindanao, unlike for the northwest Pacific as a whole, 1998–2011 was not at all a
slack cyclone period.
Until 1990, tropical cyclones rarely and sporadically made landfall on Mindanao
because it was in the ephemeral southern fringe of the northwest Pacific typhoon
track. Since the U.S.Navy Joint Typhoon Warning System began to archive northwest
Pacific tropical cyclones in 1945, only 34 visited Mindanao by February 2012 [55].
After Bopha, another 13 had arrived by February 2018 (Figure A). These 47 landfalls
are incontrovertible, and our search for what the future might hold begins with them.
During 30 of the 45years from 1945 to 1990, including the 8 years from 1956
to 1963, not one tropical depression visited Mindanao. Most of the rare Mindanao
tropical cyclones were weak: six tropical depressions and eight tropical storms.
Since 1955, five typhoons did make landfall on Mindanao before Bopha, although
Louise and Ike barely crossed northernmost Mindanao. In 1970, C4 Kate passed
45km south of New Bataan, which experienced heavy rain and floods but not much
wind. Only five tropical cyclones of all categories arrived during the northwest
Pacific peak typhoon season of June through October, although these included
Kate in October 1970 and Ike in September 1984. A total of 36 came during the off
season: 18in March through June and 18 during November through January.
In the period from 1945 to 1989, Mindanao tropical cyclones occurred only
every 2.5years on average. Then, from 1990 to 2017, they began arriving roughly
once a year. It is also troublesome that Mindanao has recently begun to suffer lethal
cyclones in consecutive years. In December 2011, a year before Bopha, Tropical
Storm Washi killed 1268 people in Cagayan de Oro City, on the northern Mindanao
coast 180 kilometers from New Bataan [56, 57]. Two months earlier, a tropical
Figure 9.
Historical record of Mindanao typhoons. (A) The record from 1945 to February 2018. Cyclone categories: TD =
tropical depression; TS = tropical storm; C1–C5 are categories increasing in strength; their respective sustained
wind speeds are given in Figure 4A. Each typhoon is dated as YY.MM.DD.Number over each TD and TS is
the month of occurrence, from 1 January to 12 December. In the insert, asterisked TDs caused fatalities. (B) The
record of all El Niño and La Niña events since 1945. From [58, 59].

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Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
DOI: http://dx.doi.org/10.5772/intechopen.81669
depression arrived in Mindanao, making 2011 only the fifth year since 1945 for the
island to receive two tropical cyclones. In 2014, Mindanao experienced Tropical
Depression Lingling and Tropical Storm Jangmi. Last, in the 5 years since Bopha, 2
tropical storms and 11 tropical depressions have visited Mindanao—so frequently
that they had to be plotted as an insert in Figure A.
The increasing frequency of Mindanao storms since 1990, although alarming,
cannot be ascribed simply to the climate change from global warming. We must
consider whether these changes are tied to multi-annual and multi-decadal fluctua-
tions in western North Pacific sea-surface temperatures.
. El Niño-Southern Oscillation (ENSO) and typhoon frequency
ENSO is the complex result of ocean-atmosphere interactions that are best
expressed by fluctuating sea-surface temperatures in the central and eastern
equatorial Pacific (Figure B), from warmer during El Niño to cooler during La
Niña periods [58, 59]. During an El Niño, atmospheric pressures are high over the
western Pacific and low in the eastern Pacific, and the situation reverses during a La
Niña. Both phases occur every 3–5 years; typically, El Niño episodes last 9 months to
a year and La Niñas as long as 3 years [60].
Tropical cyclones tend to form farther east, are more widely dispersed, and
curve northward during El Niño episodes, thus are rarer in the Philippines. During
La Niñas, their tendency is to start farther west, remain below 23°N, and take more
westward courses, and so they make more frequent Philippine landfalls, most dur-
ing a main September–November season [48, 51, 61–63]. Except for their tendency
to arrive later than November, all the typhoons before Bopha that made Mindanao
landfalls since 1945 fit that pattern by occurring during La Niñas (Figure ). Bopha
came either during a weak La Niña [64] or a weak El Niño [65]. From 1945 to 2018,
the weaker storms and depressions that visited Mindanao showed no marked
preference between El Niño and La Niña episodes, although they tended to occur
during La Niñas from 1945 to 1975 and 1996 to 2012 and during El Niños from 1979
to 1995 and 2013 to 2018.
A major analysis [66] has predicted that global warming will increase the
historical average frequency of extreme La Niñas from one every 23years to one
every 13years. Three effects of global warming are blamed: first, the western North
Pacific region of insular seas and islands that includes the Philippines is expected
to warm more quickly than the central Pacific; second, the temperature gradients
in the surface waters of the tropics will increase; and last, extreme El Niños, which
will occur more frequently, are usually followed by extreme Niñas [67]. Given the
tendency of typhoons to make landfalls on the Philippines more frequently during
La Niñas, the country including Mindanao should expect greater future storminess.
Another cycle of sea-surface temperature, the Pacific Decadal Oscillation
(PDO), is so-called because its periods last for two or three decades [68, 69]. This
cyclicity is most distinctly expressed in the northern Pacific but is not clearly mani-
fested in the tropics, although one study [70] attributes an interdecadal variation in
May-June rainfall over southern China to a complex interplay between the PDO and
the ENSO.The PDO does not correlate with Mindanao landfalls, or even with the
frequency of all northwest Pacific typhoons.
. Other expected behaviors of future typhoons
Seven prominent climate scientists who reviewed [52] the great body of
research on how climate change might be affecting tropical-cyclone activity
explain that its many conflicting results arise from great variations in cyclone

Meteorological Hazards, Climate Change and Super Storms

frequencies and intensities, as well as serious lacks in the quantity and quality
of the records. The authors are not sure that the observed changes exceed the
variability due to natural causes, but predict that by 2100 the averaged frequen-
cies of all tropical cyclones will decrease 6–34%, They also believe, however, that
intensities will increase 2–11% by century’s end because, although the frequency
of all tropical cyclones is expected to decrease, the most intense ones will become
more frequent. Importantly, the review predicts a 20% increase of rainfall within
100 kilometers of storm centers, which would generate larger debris flows. This
increase is ascribed [71] to anthropogenic warming, which weakens the summer-
time winds that carry the tropical cyclones along. Already, their translation speeds
decreased globally by 10% from 1949 to 2016. This slowing enhances the amount
of time they have to take up water vapor from the ocean and deliver rain when
their centers reach land.
In short, the record of increasingly frequent landfalls on Mindanao may or
may not indicate that more frequent typhoon disasters will happen there in the
future, although recent reports [66, 67] strongly imply as much. Low-latitude
areas, however, are given short shrift by most meteorological and climatologic
analyses. We urgently need to understand how anthropogenic global warming
is changing tropical-cyclone behavior in subequatorial regions because so many
people live in them.
. A new Philippine catalog of alluvial fans and their associated
debris-flow hazards
Following our study of the Andap disaster, Project NOAH used high-resolution
digital terrain models to identify and catalog all Philippine alluvial fans, by analyz-
ing geomorphic features, slopes, gradients, and stream networks nationwide. The
catalog is accessible online for free in the NOAH portal [72].
More than 1200 alluvial fans were identified, and communities that might be
affected by their debris flows are being educated about the hazard. In October 2015,
Typhoon Koppu (Lando) generated devastating debris flows on alluvial fans in
Nueva Ecija province, but the vulnerable communities were warned and evacuated,
and so no one was killed [73]. Later that year, Typhoon Melor (Nona) also trig-
gering massive debris flows in Mindoro Island, burying or sweeping away houses
and infrastructure in several communities situated on alluvial fans. Again, timely
warnings and evacuations prevented the loss of life [74].
. Other climate-related hazards in the Philippines and Mindanao
Future fluctuations between extreme El Niños and La Niñas pose other threats.
Philippine rainfall is modulated by ENSO; El Niños bring droughts, and La Niñas
cause excessive rainfall [75, 76]. Rock debris accumulates on slopes during a pro-
tracted El Niño drought; the succeeding La Niña episode brings heavy downpours
that mobilize the accumulated material into landslides and debris flows. Another
serious hazard associates with ENSO is forest fires: rainy La Niña episodes promote
strong vegetation growth that a succeeding El Niño drought dries out and renders
inflammable.
Mindanao has 21 active and potentially active volcanoes [77]. They are tourist
attractions, producing geothermal energy, some are actively mined, and many
support large agricultural populations. These volcanoes still lack thorough study
and monitoring instrumentation, and similar to the situation at Pinatubo Volcano

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Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
DOI: http://dx.doi.org/10.5772/intechopen.81669
on Luzon Island before its catastrophic 1991 eruption, their populations are unfa-
miliar with eruptions and lahars. Any major eruption will eventually be followed by
a large typhoon and lahars. The larger Mindanao volcanoes, being structurally and
mechanically weak [78], do not need to erupt to undergo debris flows. All that is
needed to trigger them would be exceptionally strong rainstorms in their vicinities.
. Conclusions
Bopha formed, became Category 5 Super Typhoon, and made landfall closer
to the equator than any C5 tropical cyclone ever had before. More than 120mm of
rain fell on the Mayo River watershed in only 7 hours. A catastrophic debris flow it
generated devastated Barangy Andap and killed 566 of its inhabitants. We measured
its deposit as a dry volume of 30 million m3, making it the seventh largest globally.
Debris flows are remarkably poorly understood in the Philippines. This is espe-
cially true in Mindanao because it is located in the southern fringe of the typhoon
track of the northwest Pacific and has rarely experienced typhoons and the debris
flows they generate. This lack of experience is a main cause of the loss of life in Andap.
New Bataan and Andap were established in 1968 by people who did not under-
stand the nature of the ancient debris-flow deposits on which they were building
and the hazard that produced them. This was still the case when Bopha approached:
government authorities broadcast the fatal advice for people to avoid flooding on
the high ground at Andap, which was sitting on the Mayo River alluvial fan. The
lack of understanding about debris flows persisted after the disaster; government
scientists assigned to explain the tragedy and select relocation sites for the displaced
people called it a “flash flood” [78].
New Bataan and Andap were settled in the late 1960s because of rapid popula-
tion growth. The population continues to explode and has to occupy areas vulner-
able to natural hazards. The lesson of Andap and numerous other recent disasters is
that new settlements must not be established before the hazards that threaten them
have been properly evaluated. But this is a daunting requirement, because few, if
any, safe sites remain unoccupied.
Whether or not Mindanao will experience more frequent typhoons and debris
flows is an urgent question that is very difficult to answer. In 1945, Western North
Pacific tropical cyclones began to be archived accurately; by 1990, the frequency
of Mindanao landfalls had doubled. Learning whether this is caused by anthro-
pogenic global warming is complicated by deficiencies in the quantity and quality
of the archived data and by the irregularities in the ENSO climatic rhythms. For
Mindanao, the problem is especially difficult because most of its tropical cyclones
do not arrive in the main typhoon season of July through October, and most are only
tropical depressions, which most climatologists and meteorologists do not include
as data for their models.
Philippine typhoons occur most frequently during La Niña episodes, and from
July to October, in Mindanao, however, they arrive during the off season from
November to June. Extreme El Niños and La Niñas are expected to succeed each
other more frequently. This is an excellent example of how Earth systems, which are
kept in balance by numerous interacting phenomena, oscillate vigorously when they
are disturbed. Global warming is a continuing and accelerating disturbance that
prevents returns to equilibria. Mindanao and the entire Philippine nation urgently
need to prepare their populations for more frequent hazards, including floods,
storm surges, landslides, debris flows, and forest fires.
A developing country like the Philippines has limited resources for hazard-
mitigation measures. Philippine society is intensely focused on the family, and so

Meteorological Hazards, Climate Change and Super Storms

the best and least expensive governmental approach is to provide every family with
good, easily-accessible information, so it can develop its own emergency plans.
Project NOAH’s mandate tasks are to evaluate the nation’s numerous natural haz-
ards, to educate each community about the hazards that threaten it, and to advise
them how to respond when a threat materializes. Our study of the Mayo debris flow
motivated us to identify more than 1200 Philippine alluvial fans and to prepare the
communities that its debris flows may affect. This work has already helped to save
lives from major debris flows in 2015.
Acknowledgements
This work was funded by the Philippine Department of Science and Technology
(DOST) and the Volcano Tectonics laboratory of the National Institute of
Geological Sciences at the University of the Philippines (U.P.). LiDAR data covering
the New Bataan area were provided by the U.P.Training Center for Applied Geodesy
and Photogrammetry. DOST’s Advanced Science and Technology Institute and the
Philippine Atmospheric, Geophysical and Astronomical Services Administration
provided rainfall data. We thank Congresswoman M.C. Zamora for logistical sup-
port and Thomas Pierson for the information about debris-flow mechanics.
Conflict of interest
We have no conflict of interest to declare.


© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms
of the Creative Commons Attribution License (http://creativecommons.org/licenses/
by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited.
Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
DOI: http://dx.doi.org/10.5772/intechopen.81669
Author details
Kelvin S.Rodolfo1*, A.Mahar F.Lagmay2, Rodrigo C.Eco3, Tatum Miko L.Herrero4,
Jerico E.Mendoza5, Likha G.Minimo6, Joy T.Santiago5, JenalynAlconis-Ayco7,
Eric C.Colmenares8, Jasmine J.Sabado9 and Ryanne WayneSerrado10
1 University of Illinois at Chicago, Chicago, Illinois, USA
2 UP Resilience Institute, University of the Philippines, Diliman, Quezon City,
Philippines
3 National Institute of Geological Sciences, University of the Philippines, Diliman,
Quezon City, Philippines
4 GEOMAR—Helmholtz Centre for Ocean Research Kiel, Germany
5 Nationwide Operational Assessment of Hazards Center, University of the
Philippines, Quezon City, Philippines
6 Department of Geological Sciences, University of Canterbury, Christchurch,
New Zealand
7 Development Network Consulting Services, University of the Philippines,
Quezon City, Philippines
8 KNPN Technologies, Davao City, Philippines
9 Development Academy of the Philippines, Ortigas Center, Pasig, Philippines
10 Clariden Holdings, Inc., Mandaluyong City, Philippines
*Address all correspondence to: krodolfo@uic.edu


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Super Typhoon Bopha and the Mayo River Debris-Flow Disaster, Mindanao, Philippines…
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