Hazard Impacts » Physical Vulnerability to Hazards

Introduction to Physical Vulnerability to Hazards

Physical vulnerability refers to how the natural environment and physical characteristics of a place make it more or less likely to be damaged by natural hazards. Think of it like this - some places are naturally more "fragile" when disasters strike, whilst others have built-in protection from their geography.

Understanding physical vulnerability helps us predict where hazards will cause the most damage and why some areas suffer more than others when the same type of disaster hits.

Key Definitions:

• Physical Vulnerability: The degree to which natural physical features make a location susceptible to damage from hazards.
• Hazard: A natural event that has the potential to cause damage to people, property and the environment.
• Risk: The probability that a hazard will cause harmful consequences.
• Exposure: The degree to which people, property and environment are in harm's way.

Geological Factors Affecting Vulnerability

The rocks and soil beneath our feet play a huge role in determining how vulnerable a place is to certain hazards. Different geological conditions can either amplify or reduce the impact of natural disasters.

Rock Types and Earthquake Vulnerability

The type of rock and soil in an area dramatically affects how earthquake waves travel and how much damage they cause. Understanding these differences helps explain why some areas suffer more during earthquakes than others.

🪨 Hard Bedrock

Solid granite and other hard rocks transmit earthquake waves quickly with less amplification. Buildings on bedrock generally experience less shaking and damage.

🏞 Soft Sediments

Clay, sand and loose soils amplify earthquake waves, causing more intense shaking. Areas built on reclaimed land or river deltas are particularly vulnerable.

🌊 Liquefaction Risk

Water-saturated sandy soils can behave like liquid during earthquakes, causing buildings to sink or tilt. This is especially dangerous near coasts and rivers.

Topographical Vulnerability

The shape and elevation of the land surface creates different levels of vulnerability to various hazards. Mountains, valleys, coastal plains and river basins each present unique challenges and risks.

Slope Stability and Landslide Risk

The steepness of slopes, combined with geological factors, determines how vulnerable an area is to landslides and rockfalls. Even small changes in slope angle can dramatically increase risk.

⛰ Critical Slope Angles

Slopes steeper than 15° become increasingly unstable, especially when saturated with water. Angles above 30° are particularly dangerous during heavy rainfall or earthquakes.

🌧 Valley Bottoms

Areas at the base of steep slopes face debris flow risks. Narrow valleys can funnel and concentrate landslide material, creating devastating impacts downstream.

Coastal Vulnerability

Coastal areas face unique physical vulnerabilities due to their position between land and sea. The shape of the coastline, elevation above sea level and offshore features all influence hazard impacts.

Key coastal vulnerability factors include:

• Low elevation increases flood and storm surge risk
• Soft coastlines (sand, clay) erode more easily than hard rock coasts
• Narrow beaches provide less natural protection from waves
• Funnel-shaped bays concentrate storm surge energy
• Barrier islands and coral reefs can provide natural protection

Climate and Weather Vulnerability

Local climate patterns and weather conditions significantly influence physical vulnerability to hazards. Areas with certain climatic characteristics face higher risks from specific types of disasters.

Precipitation Patterns and Flood Risk

The amount, intensity and timing of rainfall directly affects flood vulnerability. Physical features interact with precipitation patterns to create areas of high flood risk.

🌧 Drainage Basin Shape

Circular basins with steep sides concentrate rainfall quickly, creating flash flood risks. Long, narrow basins allow more time for water to flow downstream, reducing peak flood levels.

🌀 Soil Permeability

Clay soils with low permeability increase surface runoff and flood risk. Sandy soils absorb water quickly but can become saturated during prolonged rainfall.

Temperature and Drought Vulnerability

Physical characteristics of landscapes affect their vulnerability to temperature extremes and drought conditions. Some environments are naturally more resilient to water stress than others.

Factors affecting drought vulnerability:

• Soil depth and water-holding capacity
• Groundwater availability and accessibility
• Vegetation cover and root systems
• Slope orientation affecting sun exposure
• Elevation and temperature gradients

Hazard-Specific Physical Vulnerabilities

Different types of natural hazards are influenced by different physical factors. Understanding these relationships helps explain why certain areas are more vulnerable to specific disasters.

Volcanic Hazard Vulnerability

Physical vulnerability to volcanic hazards depends on distance from volcanoes, topography and prevailing wind patterns. The shape of volcanic slopes and surrounding terrain affects how volcanic products spread.

🌋 Pyroclastic Flows

Follow valleys and low-lying areas. Steep volcanic slopes accelerate these deadly flows, whilst ridges and high ground provide some protection.

🌫 Ash Fall

Wind direction determines ash distribution. Areas downwind from volcanoes face higher vulnerability, regardless of distance.

🌊 Lahars

Volcanic mudflows follow river valleys. Areas downstream from volcanoes with steep slopes and heavy rainfall face extreme vulnerability.

Reducing Physical Vulnerability

Whilst we cannot change natural physical features, understanding physical vulnerability helps us make better decisions about where to build and how to protect vulnerable areas.

Working with Natural Systems

The most effective approaches to reducing physical vulnerability work with natural processes rather than against them. This includes preserving natural flood defences and avoiding the most vulnerable locations.

🌳 Natural Flood Management

Preserving wetlands, floodplains and forests helps reduce flood vulnerability by allowing natural water storage and slowing runoff.

🏠 Land Use Planning

Avoiding development in the most physically vulnerable areas - steep slopes, floodplains, fault lines - reduces overall risk exposure.

Understanding physical vulnerability is crucial for hazard management because it helps us identify where natural disasters will have the greatest impact. By recognising these patterns, we can make informed decisions about development, emergency planning and risk reduction strategies.