Mapping Philippine Vulnerability to Environmental Disasters

Hazards may be categorized into natural and anthropogenic hazards. Climate and weather-related hazards, such as typhoons and droughts, as well as geophysical hazards, like earthquakes, volcanic eruptions and tsunamis, are natural hazards.

Anthropogenic, or man-made, hazards include deforestation, mining and climate change.

The hazard maps, particularly climate/weather-related and geophysical, were intersected with the base map from the National Mapping and Resource Information Authority (NAMRIA). The base map shows the delineation of the political boundary of each province in the country. Geographic Information Systems (GIS) software was used to overlay and multiply the hazard scores with the population density scores and the Human Development Index (HDI).

A natural hazard is defined as a natural process or event that is potentially damaging in that it may result in loss of life or injury, loss of property, socio-economic destruction or environmental degradation. Climate- and weather-related hazards, in particular, refer to the direct and indirect effects of observed changes and/or projected deviations from present-day conditions of natural climate events (such as increases and decreases in precipitation and temperature); and impacts of changes in the frequencies and occurrences of extreme weather/climate events (such as tropical cyclones, droughts, and El Niño and La Niña events).

The change in annual temperature conditions during the years 2066-2095 from the baseline period (1961-1990) was used in the hazard assessment.

Projections of changes in rainfall conditions during the dry season (December to February) and the rainy season (June to August) for the 21st century (2066-2096) were compared with the baselines data (1961-1990).

In this study, the term typhoon is used to refer to all kinds of tropical cyclones, of which there are four kinds. These are tropical depressions (<17 m/s), tropical storm ( 18-33 m/s), typhoons (34-64 m/s) and super-typhoons (>65 m/s). In general, typhoons are considered extreme weather events. Typhoons from 1945 to 2003 were included in the study.

The El Niño periods of 1982-83, 1986-87, 1992-93, and 1997-98 were considered. The Southern Oscillation Index (SOI) was used to determine inclusive months for each El Niño period. The El Niño events were compared to the monthly precipitation means of the period 1971-2000.

Geophysical events are destructive phenomena. However, these are part of the normal functioning of our dynamic planet. These so called hazards are due to naturally occurring processes in the earth's interior.

Four hazards are considered under this category: Earthquakes, earthquake-induced landslides, tsunamis and volcanic eruptions. Sources of data for these hazards include the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the Earthquake and Natural Resource Atlas of the Philippines of 1998.

A natural process that is hazardous is the movement of lithospheric plates (the solid crust and a few kilometers of the upper mantle), which causes the tectonic earthquakes. US Geological Survey defines the term earthquake as "both sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip, or by volcanic or magmatic activity, or other sudden stress changes in the earth (i.e. event by man made explosions)".

Furthermore, the resulting ground motion due to an earthquake produces another natural hazard such as landslides and tsunamis. Landslide is the downslope movement of soil and/or rock.

Tsunami is a sea wave of local or distant origin that results from large-scale seafloor displacements associated with large earthquakes, major submarine slides, or exploding volcanic islands.

One other example of a hazard is the ascent of molten material called magma beneath the earth's surface, which results to eruptions of a volcano. A volcano is a vent at the Earth's surface through which magma (molten rock) and associated gases erupt, and also the cone built by effusive and explosive eruptions.

Reviewing the natural disaster record for the Philippines, volcano and earthquake disasters are frequent in the top ten. (EM-DAT: The OFDA/CRED International Disaster Database, www.em-dat.net - Université catholique de Louvain - Brussels -- Belgium)

As with the climate- and weather-related hazards and to generate four risk maps, the resulting normalized hazard maps are multiplied with maps of normalized gridded population density by city and municipality in 2000 as well as the normalized inverse of the HDI by province in 2000.