Introduction to multiple-hazard zones

Multiple-hazard zones are areas exposed to several types of natural hazards at the same time. These locations, sometimes called disaster hotspots, face a higher risk of widespread damage because different hazards can occur close together or even overlap. This combination makes populations in these zones particularly vulnerable to natural disasters.

Key characteristics of multiple-hazard zones

Multiple-hazard zones often result from specific geographical and environmental conditions.

Examples of conditions that create multiple-hazard zones:

• Tectonic activity combined with weather events - Places near active plate boundaries might experience earthquakes and volcanoes alongside hydrometeorological hazards, which are weather-related events like cyclones or heavy rainfall.
• Mountainous terrain - Regions with steep slopes can add risks from mass movements, such as landslides.
• Climate variations - Some zones are influenced by phenomena like El Niño and La Niña, which can lead to extreme weather, including unusual sea and air temperature ranges, heavy rainfall, or prolonged droughts.

Examples of multiple-hazard zones include Japan, Indonesia, and the Philippines. These countries lie in tectonically active areas prone to earthquakes and volcanoes, while also facing frequent tropical storms.

Factors increasing vulnerability in multiple-hazard zones

In multiple-hazard zones, vulnerability is heightened because hazards can strike repeatedly without enough time for recovery.

Reasons for high vulnerability

• Frequent hazard occurrence - Multiple hazards can happen within a short period, such as in one year. This leaves little time for communities to rebuild infrastructure, restore services, or strengthen defences.
• Limited resources for recovery - Countries in these zones may lack the funding or materials needed to repair damage quickly. As a result, each new hazard can compound the effects of previous ones, leading to greater overall impacts.
• Population and poverty pressures - Rapid population growth, especially in high-risk areas like coasts, increases the number of people exposed to hazards. High poverty levels mean fewer resources for protective measures, such as sturdy housing or early warning systems.

These factors mean that even moderate hazards can turn into major disasters in multiple-hazard zones.

How multiple hazards combine to create disasters

Disasters often happen when different hazards interact or occur together, amplifying their effects.

Case study: The Philippines as a multiple-hazard zone

The Philippines provides a clear example of a multiple-hazard zone, with its location and geography making it prone to various natural threats. This archipelago consists of over 7,000 islands in Southeast Asia. Vulnerability is further increased by a rapidly growing population concentrated in coastal areas and relatively high poverty levels, which limit resilience and recovery efforts.

Volcanic hazards in the Philippines

The Philippines has around 24 active volcanoes due to its position along a destructive plate boundary where the Philippine plate is being subducted beneath the Eurasian plate.

Example: Mount Pinatubo eruption (1991):

• This eruption killed over 700 people and left approximately 200,000 homeless.
• Buildings collapsed under the weight of ash, crops were destroyed, and farmland became unusable due to ash fallout.

Seismic hazards in the Philippines

Seismic hazards involve ground shaking from earthquakes, often occurring along the plate boundary or fault lines.

Earthquake example: Luzon Island (1990):

• An earthquake measuring 7.7 on the moment magnitude scale (M_w) struck Luzon Island.
• It resulted in more than 1,500 deaths.

Tsunami example: Moro Gulf (1976):

• An offshore earthquake of 8.0 M_w generated a tsunami.
• The waves devastated coastal cities around the Moro Gulf in Mindanao, killing thousands and destroying infrastructure.

Tropical storm hazards in the Philippines

The Philippines experiences approximately 20 tropical storms annually, forming in the Pacific Ocean and tracking westwards over the islands.

Example: Typhoon Haiyan (2013):

• This powerful storm hit Tacloban and surrounding areas with intense winds and torrential rain.
• It caused flooding, landslides, power outages, and water shortages, destroying homes and leading to over 6,000 deaths.
• The total damage cost was approximately US$13 billion.

Combined hazards in the Philippines

Multiple hazards can overlap, intensifying impacts. For example, during the 1991 Mount Pinatubo eruption, Typhoon Yunya brought heavy rainfall. The rain mixed with volcanic ash to create lahars, burying communities and farmland.