Vulnerability is a key component of disaster risk. It refers to the characteristics and circumstances of a community, system, or asset that make it susceptible to the damaging effects of a hazard. Vulnerability is multi-dimensional, dynamic, scale-dependent, and site-specific. It is influenced by a range of factors, including economic, social, cultural, institutional, political, and psychological factors that shape peoples lives and the environment they live in. Vulnerability can be expressed at different scales, from human to household to community to country resolution.

Factors that affect vulnerability include population growth and distribution, social diversity, age, disability, and economic status. For example, families with low incomes often live in high-risk areas around cities because they cannot afford to live in safer places. Elderly individuals trapped in nursing facilities during Hurricane Katrina were particularly vulnerable. Vulnerable groups find it hardest to reconstruct their livelihoods following a disaster, and this in turn makes them more vulnerable to the effects of subsequent hazard events.

Reducing vulnerability is one of the main opportunities for reducing disaster risk. This involves identifying and addressing the underlying factors that make people and assets susceptible to loss and damage. Measures taken to prevent, avoid, or reduce the impact of hazards, such as building codes and early warning systems, can also help to reduce vulnerability.