Defining natural hazards

A hazard is a potential threat to human life, property, or the environment. Natural hazards specifically originate from natural processes rather than human actions. This distinction helps in categorising them and assessing their risks.

Types of natural hazards

• Geophysical hazards - These result from processes in the Earth's lithosphere (the outer layer including the crust and upper mantle). Examples include earthquakes, volcanic eruptions, landslides, and tsunamis.
• Atmospheric hazards (also known as hydrometeorological hazards) - These stem from climatic processes in the atmosphere. They encompass tropical cyclones, storms, droughts, extreme temperatures (hot or cold), and wildfires.
• Hydrological hazards - These involve the movement of water and include floods and tsunamis.

Defining disasters and their thresholds

A disaster happens when a hazard significantly affects a population, causing widespread harm that overwhelms local coping mechanisms. This impact might include loss of life, injury, economic damage, or disruption to daily life. As a result, the affected area requires external assistance to recover.

Thresholds for classifying disasters

• Loss of life - Typically, 10 or more deaths.
• Affected population - 100 or more people impacted, such as through injury, displacement, or loss of homes.
• Economic damage - Losses of at least US $2 million.

Mega-disasters

A mega-disaster extends beyond local or national boundaries, affecting regions or the entire globe.

Vulnerability and resilience in communities

Vulnerability refers to the extent to which a community or area is likely to suffer damage from a hazard, often linked to inadequate preparation. Resilience, on the other hand, is the ability of a community to withstand, adapt to, and recover from a disaster, including post-event management and preemptive planning.

Factors determining vulnerability of a community

• Geographical location - Proximity to features like coastlines or fault lines, or isolation from other areas that could provide aid.
• Demographic structure - Age and gender composition.
• Urban and population factors - High levels of urbanisation and population density.
• Socio-economic aspects - Poverty levels, wealth distribution, education, and literacy rates.

Communities with high vulnerability and low resilience have a lower disaster threshold, meaning even a moderate hazard can escalate into a disaster. Conversely, resilient communities raise this threshold through awareness and mitigation strategies.

Graphing resilience and vulnerability

To visualise these concepts, consider a graph where resilience is plotted against vulnerability. A downward-sloping line illustrates that high resilience paired with low vulnerability creates a high disaster threshold (disasters are less likely), while low resilience and high vulnerability lead to a low threshold (disasters are more probable). This relationship underscores the importance of building resilience to counter vulnerability.

Models explaining hazards and disasters

The Degg model

The Degg model uses a Venn diagram to show the overlap between a natural hazard event and a vulnerable population, resulting in a disaster. The larger the hazard or the more vulnerable the people, the greater the disaster's scale. This model emphasises that disasters are not just natural events but require human exposure to occur.

The Hazard Risk Equation

Risk represents the potential for a disaster, combining hazard characteristics with societal factors. The Hazard Risk Equation quantifies this, helping to identify high-risk areas.

Formula for the Hazard Risk Equation:

$\text{Risk}=\frac{\text{hazard}\times \text{vulnerability}}{\text{capacity to cope}}$

Where:

• Hazard - The intensity or magnitude of the natural event.
• Vulnerability - The susceptibility of the population, as influenced by factors like poverty or location.
• Capacity to Cope - Equivalent to resilience, including resources for response and recovery.

Increases in hazard magnitude or vulnerability heighten risk, while stronger coping capacity reduces it. Governments often focus on boosting capacity, as preventing hazards like earthquakes is impossible.

Factors increasing hazard risk

Certain characteristics of hazards amplify their potential to cause disasters.

The Pressure and Release (PAR) model

The PAR model maps how vulnerability builds over time, leading to disasters when combined with a hazard. It views disasters as the "pressure" from accumulating stresses, released only by addressing root causes or the hazard itself.

The model shows a progression of vulnerability:

1. Root causes - Fundamental issues like limited access to resources, weak political or economic systems.
2. Dynamic pressures - Resulting stresses, such as lack of education, insufficient investment, high debt, or rapid urban migration.
3. Unsafe conditions - Immediate vulnerabilities, including poor building standards, low incomes, absent welfare systems, and inadequate infrastructure.

These layers intersect with a hazard (e.g., earthquake, tsunami, or volcanic eruption) to produce a disaster. The model highlights that developed countries often face fewer root causes, reducing their overall vulnerability.