[IPCC] Hazard is the possibility of a physical event or event pattern, which could be either natural or human-caused, that has the capacity to result in loss of life, injury, or other detrimental health effects, as well as property, infrastructure, livelihoods, service provision, ecosystems, and environmental resource damage and loss.

Hazard is any kind of action/event that has a potential danger in itself. Some actions, such as driving a car and traveling by plane, have the potential to cause an adverse event, i.e. a negative impact that can be damage or loss. These activities can trigger a sequence of dangerous events that can result in a hazardous situation (e.g. driving a car on poorly maintained roads). This hazardous situation can activate existing vulnerabilities in the car/driver, e.g. worn tires, the driver's lack of driving experience, leading to an exposure to danger and therefore potentially resulting in an adverse event (e.g. a collision, a rollover, etc.).

A hazard event grounds urban risks. An urban risk is a relation between a risk driver and a urban system at risk that indicates any occurrence of potential damage or loss to the urban system. The impact of the risk can be measured according to the value attributed to the elements (potentially) affected by the risk and by the hazard.

In turn, hazard situations trigger hazard events. This means that the existence of a set of Hazardous Situations can result in a set of (contingent) Risks. The relation between the risk driver and the urban system at risk is based on these events. In turn, a hazard events can lead to a chain of hazard events. 

[IPCC] "Exposure is the presence of people, livelihoods, species or ecosystems, environmental functions, services, and resources, infrastructure, or economic, social, or cultural assets in places and settings that could be adversely affected."

Impacts are events that  result in situations of impacts on urban systems. It is a type of one or more resulting events from realized risks. In the context of climate change, the consequences of realized risks on natural and human systems, where risks result from the interactions of climate-related hazards (including extreme weather/climate events), exposure, and vulnerability.