**7. 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 analyzing 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 triggering 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].

### **8. 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 protracted 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 on Luzon Island before its catastrophic 1991 eruption, their populations are unfamiliar 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.

### **9. Conclusions**

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 *frequencies* 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 summertime 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

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

Following our study of the Andap disaster, Project NOAH used high-resolution digital terrain models to identify and catalog all Philippine alluvial fans, by analyzing geomorphic features, slopes, gradients, and stream networks nationwide. The catalog is accessible online for free

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 triggering massive debris flows in Mindoro Island, burying or sweeping away houses and infrastructure in several communities situated on alluvial fans.

**7. A new Philippine catalog of alluvial fans and their associated** 

Again, timely warnings and evacuations prevented the loss of life [74].

**8. 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 protracted El Niño drought; the

reach land.

so many people live in them.

100 Climate Change and Global Warming

**debris-flow hazards**

in the NOAH portal [72].

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 especially 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 understand 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 population growth. The population continues to explode and has to occupy areas vulnerable 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 anthropogenic 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.

**Author details**

Kelvin S. Rodolfo<sup>1</sup>

Jerico E. Mendoza<sup>5</sup>

Eric C. Colmenares8

Quezon City, Philippines

Quezon City, Philippines

Philippines

**References**

\*, A. Mahar F. Lagmay<sup>2</sup>

, Jasmine J. Sabado<sup>9</sup>

, Likha G. Minimo<sup>6</sup>

1 University of Illinois at Chicago, Chicago, Illinois, USA

4 GEOMAR—Helmholtz Centre for Ocean Research Kiel, Germany

\*Address all correspondence to: krodolfo@uic.edu

8 KNPN Technologies, Davao City, Philippines

10 Clariden Holdings, Inc., Mandaluyong City, Philippines

, Rodrigo C. Eco3

and Ryanne Wayne Serrado<sup>10</sup>

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

, Joy T. Santiago5

2 UP Resilience Institute, University of the Philippines, Diliman, Quezon City, Philippines

5 Nationwide Operational Assessment of Hazards Center, University of the Philippines,

6 Department of Geological Sciences, University of Canterbury, Christchurch, New Zealand 7 Development Network Consulting Services, University of the Philippines, Quezon City,

[1] Rodolfo KS, Lagmay AMF, Eco RC, Herrero TM, Mendoza JE, Minimo LG, et al. The December 2012 Mayo River debris flow triggered by Super Typhoon Bopha in Mindanao, Philippines: Lessons learned and questions raised. Natural Hazards and Earth System

[2] Ea C, Lebumfacil MA, Silveron JM, Juson B. Proposal to Declare Certain Areas in New Bataan Identified as Highly Susceptible to Landslide and Flooding Geohazard [Internet]. 2013. Available from: https://www.academia.edu/5054503/POLICY\_PROPOSAL\_TO\_ DECLARE\_CERTAIN\_AREAS\_IN\_NEW\_BATAAN\_IDENTIFIED\_AS\_HIGH\_TO\_ LANDSLIDE\_AND\_FLOODING\_AS\_NO\_BUILD\_ZONE [Accessed: November 24, 2015]

[3] 1970 Census of Population and Housing Final Report for Davao del Norte. National Census and Statistics Office. Manila; National Economic and Development Authority; 1974. p.1 [4] National Statistics Office. Total Population by Province, City, Municipality and Barangay as of May 1, 2010. Compostela Valley, Census of Population and Housing [Internet].

3 National Institute of Geological Sciences, University of the Philippines, Diliman,

9 Development Academy of the Philippines, Ortigas Center, Pasig, Philippines

Sciences. 2016;**16**:2683-2695. DOI: 10.5194/nhess-16-2683-2695

, Tatum Miko L. Herrero<sup>4</sup>

http://dx.doi.org/10.5772/intechopen.81669

, Jenalyn Alconis-Ayco<sup>7</sup>

,

103

,

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 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 hazards, 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 support and Thomas Pierson for the information about debrisflow mechanics.

### **Conflict of interest**

We have no conflict of interest to declare.
