Understanding and Mitigating Natural Disaster Risks
Natural Disaster Risks
Probability of Natural Risks
Natural risk is the probability of a natural process causing damage or catastrophe to a population. The return period for each type of event is the time elapsed since the last occurrence, influencing the likelihood of recurrence.
Types of Natural Risks
Natural risks stem from geological, atmospheric, or hydrological phenomena. These processes can be endogenous (internal) or exogenous (external). When the internal dynamics of these processes manifest at a specific time, an event occurs. A catastrophe occurs when an unexpected event results in significant damage to human activity.
Evaluating Risk Factors
- Natural process risk: The potential of the natural process to cause environmental changes.
- Social catastrophe: The impact of the event on human populations.
- Interference: Human activities that can exacerbate the risk.
- Damage: The extent of the harm caused by the event.
Hazard assessment estimates the potential for environmental change, regardless of human activity. Preventive measures can reduce the natural hazard by acting on the process itself or by influencing the population to avoid interference.
Catastrophe and Damage
A catastrophe transforms risk into actual damage. The magnitude of economic costs depends on the scale of the catastrophe.
Characteristics of Affected Areas
The impact of a natural process depends on the characteristics of the affected area and the population’s activities.
Risk Scale
- Risk-free zone
- Area with very low, purely assumable risk
- Area with affordable, low risk
- Medium risk area
- Area of high risk
- Very high-risk area
Risks from Internal Dynamics
- Seismic (earthquakes)
- Volcanic
- Caused by deformation
Risks from External Dynamics
- Erosion
- Gravitational processes related to geological characteristics of the subsoil
- Glacial and snow-related processes
- River dynamics
- Coastal processes
- Atmospheric dynamics
The 3 Key Approaches
- Prediction: Attempting to know what will happen before a phenomenon occurs.
- Forecasting: In-depth study to statistically define the risk, anticipating the likelihood and intensity of a phenomenon.
- Prevention: Measures and activities based on prediction and forecasting to mitigate impact.
Risk Mapping
Geological mapping identifies potential risks and affected areas.
Mitigation
Mitigation involves implementing decisions and measures before a disaster to reduce its consequences.
Reducing Impacts
- Improving understanding of geodynamic phenomena
- Sharing scientific knowledge among countries
- Implementing adequate management policies
- Increasing information and awareness campaigns
Disaster Risk Index (IRD)
The IRD measures and compares risks between countries.
Seismic Risk (Earthquakes)
Seismic effects include building damage, soil displacement, landslides, and tsunamis.
Factors Increasing Earthquake Risk
- High population density in fracture zones
- Crowded neighborhoods in poor countries
Earthquake Prediction and Prevention
Precursors to earthquakes can include tremors, ground deformations, changes in electromagnetic fields, and water levels in wells. Prevention measures include ensuring infrastructure integrity for post-earthquake services, restricting construction near known faults, reinforcing building structures, and promoting insurance.
Volcanic Risk
Volcanic risks are less perceptible than earthquakes due to long periods of inactivity.
Volcanic Risk Prevention
Prevention involves constant monitoring for signs of eruption, such as increased seismic activity, ground elevation, changes in electromagnetic fields and thermal flow, gravity anomalies, and changes in fumarole gases.
Erosion Risk
Erosion is the removal of materials by external geological processes. It poses a risk due to resource loss and material mobilization.
Factors Increasing Erosion Risk
- Steep slopes
- Lack of vegetation
- Low soil cohesion
- Arid climate
Erosion Prevention
- Appropriate land use based on erosion sensitivity
- Reforestation and vegetation management
Risks Associated with Gravitational Processes
These risks can be caused by natural factors or human activity.
Landslide Risk
Landslides can bury people and infrastructure.
Landslide Prevention
- Reducing slope inclination
- Removing weight at the top and reinforcing the base
- Drainage
- Reinforcement
Risks Associated with Subsurface Processes
- Subsidence (ground sinking)
- Collapse
- Karst formations
Risks Associated with River Dynamics
The most significant risk is flooding due to increased flow.
Flood Disasters
- Loss of life and livestock
- Economic losses
- Infrastructure damage
Risks Associated with Coastal Processes
These risks are due to the action of the sea on rocks and sediments along the coast.
Causes of Flooding
- Weather conditions
- Snowmelt
- Coastal flooding
- Levee breaches
- Natural and anthropogenic causes
Storms and Cyclones
Large storms intensify the impact of the sea. High wind speeds can cause significant damage. Cyclones originate from warm air masses over warm waters near the equator, causing strong winds and rains. They are called hurricanes in the Caribbean, typhoons in the Indian and Pacific Oceans, and cyclones in the Indian Ocean.
Cold Air Drops
Cold air drops occur in temperate regions bordering subtropical zones. They are storms not associated with warm or cold fronts.
Disaster Classification
Disasters are classified by their origin: natural or anthropogenic.
Catastrophe Definition
A catastrophe results from the interaction of exceptional events with a vulnerable population.
Main Effects of Catastrophes
- Economic losses
- Disruption of environmental development
Factors Increasing Disaster Risks
- Uncontrolled population growth
- Underdevelopment
- Inadequate urbanization
- Inappropriate use of high-risk technologies
- Environmental degradation
- Climate change