Suitability Map for Leyte Island, Philippines by AX Digital Palette Designs

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RESIDENTIAL BUILDING SUITABILITY MAP FOR LEYTE ISLAND, PHILIPPINES

Imprint As a federally owned enterprise, we support the German Government in achieving its objectives in the field of international cooperation for sustainable development. Items from the named author does not necessarily reflect the views of the publisher. Published by Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH Registered offices Bonn and Eschborn, Germany T +49 228 44 60-0 (Bonn) T +49 61 96 79-0 (Eschborn) Responsible Max-Johannes Baumann Environment and Rural Development Program Program Director and Principal Advisor 2/F PDCP Building, Rufino cor. Leviste Streets, Salcedo Village, Makati, Philippines T +63 2 892 9051 I: www.enrdph.org E: max.baumann@giz.de Source and Copyrights © 2015 GIZ Author Olaf Neussner of Arken Consulting

Arken Consulting GmbH Ackerstr. 11b 10115 Berlin, Germany Phone: +49 -30 - 200 541 51 berlin@arken-consulting.com www.arken-consulting.com Layout / Design Ryan G. Palacol Copyright on Photos Benni Thiebes, Johannes Anhorn, Dave Martinez, Thomas Fischer, Olaf Neussner Maps The geographical maps are for information purposes only and do not constitute recognition under international law of boundaries and territories. GIZ does not guarantee in any way the current status, accuracy or completeness of the maps. All liability for any loss or damage arising directly or indirectly from their use is excluded. Printed and distributed by Environment and Rural Development Program Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH Place and date of publication Manila, Philippines September 2015

Table of Contents Acronyms & abbreviations ��

Summary �� iii Acknowledgement �� iv

1 Top reasons to use building suitability maps ��

2 Actual benefits and gains ��

3 Success factors �� 12 4 Obstacles and limitations �� 14 5 Development of suitability maps �� 16 5.1 Typhoon (Wind hazard) �� 22 5.2 Storm Surge �� 27 5.3 Earthquakes �� 32 5.4 Tsunami �� 40 5.5 Flood �� 43 5.6 Landslide �� 46 5.7 Ground Rupture �� 48 6 Appendix: Data sources �� 51 7 Literature �� 52

Residential Building Suitability Map for Leyte Island, Philippines

Acronyms & Abbreviations CAPRA DEM GIS GIZ JICA LGU MGB MMI NOAH PGA PEIS PHIVOLCS SRTM SSA USGS WS

Probabilistic Risk Assessment Program Digital Elevation Model Geographic Information System Deutsche Gesellschaft fĂźr Internationale Zusammenarbeit Japan International Cooperation Agency Local Government Unit Mines and Geosciences Bureau Modified Mercalli Intensity National Operational Assessment of Hazards Peak Ground Acceleration Philippine Earthquake Intensity Scale Philippine Institute of Volcanology and Seismology Space Shuttle Radar Topographic Mission Strom Surge Advisory United States Geological Survey Wind Speed

Residential Building Suitability Map for Leyte Island, Philippines

Summary After typhoon Haiyan (local name Yolanda) struck the Philippines in November 2013 discussions evolved around the question â&#x20AC;&#x153;where is it safe to build and where is it not?â&#x20AC;?. Hazard maps were consulted and it quickly became clear that they do provide only part of the information needed. What the maps didnâ&#x20AC;&#x2122;t provide was the likelihood or probability of the occurrence of a certain type of hazard in a certain area. This is crucial information to assess if and how often of a certain hazard might happen in a certain area. GIZ addressed this need by developing a map that integrated different hazards and the probability of their occurrence. With this map land use planners are able to quickly assess the risks for normal residential buildings anywhere in Leyte as well as to assess risks for future projects and structures. For example, the map shows that some areas have 5% or more expected annual damage. This means statistically the value of a residential building is wiped out in 20 or less years by the accumulated damages it sustains. The production of the map included a survey of available hazard and vulnerability related information and data. The most reliable and appropriate sources were chosen and processed in a Geographic Information System. The first version of the map was provided to Local Government Units in Leyte in the middle of 2014. This second version includes a lot of improvements, such as one more hazard and more details. The map reveals big differences in the risk level of different areas. The flat coastal areas in the east of the island are more exposed to severe coastal hazards (storm surge and tsunami) than other coasts and with this they are the most dangerous spots in Leyte. Contributing to this is also the earthquake and the storm hazard. Both are more severe in the north east than the south west of the island. Some areas are facing relatively low risk levels. This applies to some spots with only ground shaking and storm as possible hazards.

iii

Residential Building Suitability Map for Leyte Island, Philippines

Acknowledgement GIZâ&#x20AC;&#x2122;s work on risk maps for Leyte started in 2008 and was inspired by University of Twente (ITC) Associate Professor Norman Kerle, who introduced the concept back then to the author. A number of German geographers contributed their skills and knowledge to the development of various approaches over the years, namely Katharina Wilkin, Benedikt Hahn, Hannah Fuchs, and Henning Goetz. However, the bulk of the GIS-related work for the building suitability map was done by Bastian Schneider, partly in night shifts because of the slow computers. GIS and other data were kindly provided by PHIVOLCS (Dr. Leonida Bautista), Project NOAH (Prof. Dr. Mahar Lagmay), and Weihua Fang (Beijing Normal University). Preparing the map was a team effort and without the contributions of each member the final result would not have been possible. Last but not least Dolores Nuevas needs to be mentioned. She is a tireless promoter of the map in the Local Government Units of Leyte and Soutern Leyte.

Top reasons to use building suitability maps map combines all important hazards and there is no • One need to consult many hazard maps for planning settlements.

suitability map includes the different probabilities of • The different hazards and thus weighs the hazards by their

impact. most detailed and reliable sources of information were • The chosen from many available sources.

suitability map shows quantitative data (percent • The damage per year). This is a sound foundation for judging

the acceptability of the risk.

Residential Building Suitability Map for Leyte Island, Philippines

Actual benefits and gains

Land use planners have to take into account many factors when they consider future spatial developments. One of them is the threat posed by natural disasters. The standard method of assessing the danger level of locations is consulting hazard maps. In the Philippines, a relatively large number of hazard maps exist in various scales. But for one, these maps often come in formats not suitable for spatial analysis (printed maps or pixel files) and it is extremely cumbersome to overlay the different hazards in GIS used by planners. Even if the hazard maps exist in GIS ready vector files, overlaying them results in a confusing multitude of hazards in most places. Second, these maps do not weigh the hazards by importance. The current hazard maps rarely provide information needed to assess the relative importance of one hazard compared to another. They mostly show categories like “low, medium, high susceptibility” to a hazard, but it is often unclear what “low, medium, high” really mean. GIZ addressed this issue by considering the frequency and intensity of major hazards in Leyte Island. This revealed that some hazards are much more important than others because they occur often with dangerous severity while others are rare and/or not very intense. One of the main features land use planners are concerned with is where people shall reside and live. Typical residential houses in the Philippines in rural areas have one or two floors, are made of steel reinforced concrete columns and bricks (hollow blocks) as walls. Such houses have typical sensitivities to the forces of extreme natural events. Certain hazard intensities cause specific damages to buildings. Combining such vulnerabilities with the frequency and intensity of various hazards gives a good picture of the danger normal residential buildings are facing. The impact on the buildings can be expressed as the expected percent average damage per year (calculated in % of the value of the building?). These data are easily comparable and one can add the expected damages from different hazards easily. The building suitability map shows the multi hazard impact on residential buildings and thus reduces the many hazard maps to one single map. Furthermore the suitability map displays quantitative data (percent annual damage) and thus gives concrete indications on the danger level in specific locations. In a GIS, the land use planner can also see the composition of the different risks. This helps to identify hazard specific counter measures (e.g. building elevated in flood prone areas). Furthermore, in GIS it is easy to display areas above and below user defined risk levels. The economic feasibility of such activities may be assessed with a costbenefit-analysis.

Residential Building Suitability Map for Leyte Island, Philippines

One Single Map for Multiple Hazards Obviously it is much easier consulting one map than many. GIZ did this by considering the severity and return period of major hazards. As landslides and ground rupture are hazards which, strictly speaking, do not return at the same place in the same manner, they are marked on the map but they are not part of the calculations. In total the risks for residential buildings caused by seven hazards are displayed on one single map. Risk from seven hazards displayed in one map The risk is displayed as expected annual damage in percent of the value of the building.

Residential Building Suitability Map for Leyte Island, Philippines

Quantitative Data Display of Danger Level The exposure to different natural hazards differs a lot. There are hazards expected only in specific locations (floods usually in planes or near rivers, tsunamis and storm surges in coastal areas and landslides in mountainous landscape) but other hazards cover large areas (storm, ground shaking QUANTITATIVE RISK VISUALIZATION

Residential Building Suitability Map for Leyte Island, Philippines

caused by earthquakes). However, hazards also show strong local variations as valleys are to some degree protected from strong winds while mountain top edges experience higher wind speeds. The same is true for earthquakes. The actual ground shaking depends a lot on soil characteristics.

The resulting map enables house owners to see how dangerous a specific place is. This applies to plans for future settlements as well as to existing houses. This might be of interest for the insurance industry to determine premiums based on the level of exposure to risk.

Residential Building Suitability Map for Leyte Island, Philippines

User Defined Risk Levels Risks caused by natural hazards can never be reduced to zero as no place on earth is absolutely free from all hazards, but what level of risk is acceptable, depends largely on individual perception. In some places in Leyte the value of a residential house may be completely gone by extreme events within 20 years (5% annual damage), while in other locations this may take more than 100 years (<1% annual damage). Local or national political decision-makers may define acceptable risk levels and produce maps showing areas below and above such risk threshold. The private sector may also find such maps helpful. Investors looking for relatively safe locations for a new subdivision (or a factory) can define a risk level and have all suitable areas displayed in one color and the too dangerous areas in another color.

IN THE AREA OF TANAUAN, TABON TABON AND TOLOSA IN LEYTE

1% Expected Annual Damage

2% Expected Annual Damage

These three maps show that places with less than 1 % risk are very rare and relatively few locations have less than 2 % risk, but most locations are exposed to less than 3 % expected annual damage to residential buildings. It is a political decision what level of risk is perceived to be acceptable with respect to land use planning. “No build zones” may be declared or “safe” areas for new settlements can be identified based on a certain risk threshold. Ordinances may also include mitigation and preparedness measures for zones. This could be ground shaking resistant design and construction obligations or higher and sturdier buildings in coastal areas faced by big ocean waves. It is also an individual decision what type and level of danger is acceptable to a house owner and the value of property might be influenced by the exposure of a lot to different hazards.

Residential Building Suitability Map for Leyte Island, Philippines

3% Expected Annual Damage

Residential Building Suitability Map for Leyte Island, Philippines

Display of the Contribution of Different Hazards to the Total Risk Though the risk to damages is displayed as a single value for a particular spot or area, it is possible to see the contribution of different hazards to the total hazard. In the example shown below two small areas are displayed with the composition of their risk data. The point on the east is a the coast and typical coastal hazards contribute most of the risk, while further to the west, tsunami and storm surge are less important. With GIS software the values for any point may be retrieved.

COMPOSITION OF THE RISK FOR RESIDENTIAL BUILDINGS FOR AN INLAND AND A COASTAL AREA

Deutsche Gesellschaft fĂźr Internationale Zusammenarbeit (GIZ) GmbH Registered offices Bonn and Eschborn, Germany 2B PDCP Bank Center, V.A. Rufino corner L.P. Leviste Sts. Salcedo Village, Makati City, Philippines Contact Dr. Walter Salzer Program Director and Principal Advisor Environment and Rural Development Program Tel. +63 2 892 9051 Fax +62 2 892 3374 Email: walter.salzer@giz.de www.enrdph.org