[IPCC] Adaptation in in human systems is the process of adjustment to actual or expected risk driver and its effects, in order to moderate harm or exploit beneficial opportunities.

[IPCC]

"Exposure is defined as 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."  

Source: https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_Annex-II.pdf

Exposure is a necessary but not sufficient determinant of risk. It is possible to be exposed but not vulnerable. However, to be vulnerable to an extreme event, one must also be exposed.

Source: O.D., M.K. van Aalst, J. Birkmann, M. Fordham, G. McGregor, R. Perez, R.S. Pulwarty, E.L.F. Schipper, and B.T. Sinh, 2012: Determinants of risk: exposure and vulnerability. In: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation[Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (eds.)]. A Special Report of Working Groups I and II of the Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, UK, and New York, NY, USA, pp. 65-108.

Exposure event is the action of dispose 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 by hazards.

[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. 

An agentive object (Person or Artificial Agent) who assigns a hazard value to a situation.

Hazardous situations are circumstances in which people, infrastructures, urban spaces or the environment is/are exposed to one or more harms.

Hazard is a situation that contains "a source of energy or physiological factors and behaviors that, if uncontrolled, will lead to harmful/harmful events/occurrences" (Shinar, Gurion, and Flascher, 1991, p. 1095, apud. Grimaldi and Simonds, 1984, p. 236).

Hazard is a condition or set of circumstances that has the potential to cause or contribute to injury or death" (Sanders and McCormick, 1993, p. 675).

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.

Impact response in an urban context involves a two-pronged approach: mitigation of the impacts on urban systems and adaptation of urban systems to non-controlled situations.

Impacts generally refer to effects on lives, livelihoods, health and well-being, ecosystems and species, economic, social, and cultural assets, services (including ecosystem services), and infrastructure. Impacts may be referred to as consequences or outcomes and can be adverse or beneficial. In the model, only the type of adverse impact.

Impacts are also defined as the quantification of the overall potential damage and losses that a reference event may generate in the same area and in a set timeframe.

Effects on natural and human systems. In this report, the term ‘impacts’ is used to refer to the effects on natural and human systems of physical events, of disasters, and of climate change.

Source: https://archive.ipcc.ch/pdf/special-reports/srex/SREX-Annex_Glossary.pdf

It is the value given to the impact caused by the risk event that has occurred or is estimated. The level of impact is directly proportional to the damage and losses that have occurred or could occur as a result of the event.

An agentive object (Person or Artificial Agent) who assigns a impact value to a situation of risk event impact.

Loss (resulting from being deprived of something) is a measure (quantified or not) of the damage or destruction caused by a disaster. This includes the loss of human life in dangerous events.

Material damage, also known as property damage, is damage to a person's assets or urban system`s assets, i.e. the loss of goods or things that have economic value. Material damages include losses actually suffered (emergent damages), as well as amounts that the person has failed to receive (lost profits).

 Mitigation is defined as the implementation of actions or activities that are designed to limit the adverse impacts caused by hazardous events and urban risks that have already occurred.

Decreased integrity, size, efficiency (function), or conditions that are not considered beneficial by a community as a result of an adverse event. Depending on the application, damage can be measured in different ways, using metrics appropriate for each type of risk analysis. In particular, non-physical damage affects the social life of an urban system. This type of damage is understood as a measure of social disruption, in terms of deterioration of social relations and functions, that a natural or anthropogenic event causes to a community in the short to medium term (i.e. homelessness) or psychological symptoms in a part of the population, such as anxiety, panic syndrome, correlated with the possibility of new occurrence of the risk events.

An object at risk is any agentive or non-agentive object that is exposed to a hazardous situation or is vulnerable to certain hazardous situations. 

1. [IPCC] Any natural or human-induced factor that directly or indirectly causes a change in a system (adapted from MA, 2005).

2. It encompasses both natural and human-induced factors, processes, or conditions that result in a direct or indirect alteration of a system.

Available at: https://civil-protection-knowledge-network.europa.eu/eu-overview-risks

Source: Åsa Boholm & Hervé Corvellec, 2011. "A relational theory of risk," Journal of Risk Research, Taylor & Francis Journals, vol. 14(2), pages 175-190, February.

In risk-oriented urban systems, a risk object is specialized as a Risk Driver. 

It is a relational structure that links Risk Drivers and Urban Systems at Risk.

In the case of urban systems, risks are assessed based on two different types of phenomena: 1) natural phenomena; and 2) man-made phenomena. Natural phenomena are events that do not have a human cause; examples include earthquakes, tsunamis, and solar storms. Conversely, human phenomena are events caused by human action. For example, pollution, urbanization, extensive monoculture, and deforestation.

[IPCC] Risk is defined by IPCC v.6 as the potential for adverse consequences for human or ecological systems, recognizing the diversity of values and objectives associated with such systems.

In the context of climate change, risks can arise from potential impacts of climate change as well as human responses to climate change. Relevant adverse consequences include those on lives, livelihoods, health and well-being, economic, social and cultural assets and investments, infrastructure, services (including ecosystem services), ecosystems and species.

In the context of climate change impacts, risks result from dynamic interactions between climate-related hazards with the exposure and vulnerability of the affected human or ecological system to the hazards. Hazards, exposure and vulnerability may each be subject to uncertainty in terms of magnitude and likelihood of occurrence, and each may change over time and space due to socio-economic changes and human decision-making (see also risk management, adaptation and mitigation).

In the context of climate change responses, risks result from the potential for such responses not achieving the intended objective(s), or from potential trade-offs with, or negative side-effects on, other societal objectives, such as the Sustainable Development Goals (SDGs) (see also risk trade-off). Risks can arise, for example, from uncertainty in implementation, effectiveness or outcomes of climate policy, climate-related investments, technology development or adoption, and system transitions.

Source: https://www.ipcc.ch/site/assets/uploads/2021/02/Risk-guidance-FINAL_15Feb2021.pdf

An Urban System is a human-made system placed in a specific space and time. It is composed of essential parts, which are Infrastructure, Geosphere, and Population. Population is a collective of agents who live or use the urban space and the tangible Infrastructure (hard infrastructure) through services (soft infrastructure). In turn, the Urban Space (Geosphere) is the territory, the place where the population (resident or non-resident) lives or uses the soil as well as where the infrastructure is located.

An urban system is a set of interconnected parts (population, urban space, and infrastructure). An urban system at risk has one or more parts vulnerable or exposed to certain risk drivers in certain situations.

The propensity or predisposition to be adversely affected. Vulnerability encompasses a variety of concepts and elements, including sensitivity or susceptibility to harm and lack of capacity to cope and adapt.

Vulnerability expresses the relationship between the intensity of an adverse event, the features of the elements at risk (assets, community, system, environment) that affect their behavior, and the measure of the damage resulting from the event (response). Uncertainty in assessing vulnerability is due to insufficient knowledge of the features affecting the response and the possible effects on the elements exposed to an event.

Vulnerability is defined in different ways depending on the types of risk being assessed. In seismic risks, vulnerability is the probability that an element at risk, belonging to a specific behavioral class (vulnerability class), experiences or exceeds a damage threshold (according to a predetermined scale of damage) upon the occurrence of an event of an assigned intensity. In flood risks, vulnerability expresses the expected damage to the elements at risk, the extent of damage ranging from 0 (no damage) to 1 (total destruction).