Imagine two houses standing side by side, both of similar height and located in the same neighborhood. One is built with reinforced concrete, while the other is constructed of masonry. When an earthquake strikes, both houses experience the same shaking, yet the consequences differ: the reinforced concrete house remains intact, while the masonry house suffers visible damage. If both houses experienced the same hazard, what explains the difference in their risk?

To understand this, let’s break the situation. The earthquake itself is the hazard—a potentially damaging event. United Nations Office for Disaster Risk Reduction describe hazard as a process, phenomenon, or human activity that can cause loss of life, injury, or damage to property and the environment. But a hazard alone does not cause damage unless something is in its path. Since both houses are located in the same area, they are equally exposed to that hazard. Exposure simply means being present in a hazard-prone location, or more formally, the presence of people and assets in places that could be affected by hazards.

Now, even though the hazard and exposure are the same, the damage is not. This is where vulnerability comes in. Vulnerability describes how susceptible something is to damage. The United Nations Office for Disaster Risk Reduction further explains vulnerability as the conditions (physical, social, or economic) that increase the likelihood of damage. In this case, the masonry house is more brittle and less resistant to seismic forces. Hence, it is more vulnerable than the reinforced concrete house, which is consists of reinforcement bars and is able to sustain seismic loads better.

When you combine these three—hazard, exposure, and vulnerability—you get risk. In simple terms, risk explains the likelihood and severity of damage. In disaster risk studies, including frameworks used by organizations such as the Asian Disaster Reduction Center, this relationship is often expressed as:

Risk = Hazard × Exposure × Vulnerability

So, in this example, both houses face the same hazard and exposure, but the masonry house has a higher risk because it is more vulnerable.

This also shows an important point. We cannot always control hazards like earthquakes, and we often cannot change where buildings are located. But we can reduce vulnerability. Better design, proper materials, and following building codes can make structures more resistant. In other words, even if hazard and exposure stay the same, improving vulnerability is how we reduce risk.

NOTE: Featured Image adapted from Oom et al. (2022), Pan-European wildfire risk assessment.