Individual risk evaluation for landslides: key details.

Area of Science:

• Geoscience
• Risk Management
• Environmental Science

Background:

• Risk-taking is inherent in life, involving intuitive comparisons of perceived risks and benefits.
• Quantitative risk management frameworks compare estimated risks against tolerable thresholds for safety decisions.
• Established landslide risk management methods have consensus on tolerable life-loss thresholds, but nuances require exploration.

Purpose of the Study:

• To refine landslide risk management by improving risk communication and estimation methods.
• To address the limitations of current tolerable risk thresholds and the As Low As Reasonably Practicable (ALARP) principle.
• To provide practical tools for communicating risk estimates and thresholds to stakeholders.

Main Methods:

• Proposing the use of the micromort (1 in 1 million life loss risk) as a standardized unit for risk communication.
• Providing guidance on defining and combining landslide scenarios for risk estimation.
• Analyzing the limitations of the ALARP principle and suggesting proportionality-based conditions for risk tolerance.

Main Results:

• The micromort unit can enhance the clarity of risk estimates and thresholds.
• Unquantified risks from low-probability/high-consequence scenarios need to inform management decisions.
• The 'gross disproportion' condition of ALARP is often unachievable; proportionality is a more applicable criterion for risk tolerance.

Conclusions:

• Adopting the micromort unit can improve public and decision-maker understanding of landslide risk.
• Risk management requires careful consideration of scenario definition and the inclusion of unquantified risks.
• Risk tolerance thresholds should be context-specific, moving beyond rigid or unachievable criteria like gross disproportionality.