Glossary R


Receptor refers to the entity that may be harmed (a person, property, habitat etc.). For example, in the event of heavy rainfall (the source) floodwater may propagate across the flood plain (the pathway) and inundate housing (the receptor) that may suffer material damage (the harm or consequence). The vulnerability of a receptor can be modified by increasing its resilience to flooding.

Source: FLOODsite

Record (in context)

Not distinguished from event (see Event)

Source: FLOODsite

Recovery time

The time taken for an element or system to return to its prior state after a perturbation or applied stress.

Source: FLOODsite

Relocating the building

Moving a building out of the floor area, a kind of flood proofing measures.

Source: FLOWS

Remote sensing

The observation of the earth or atmosphere from space with satellites or from the air using aircrafts is called Remote Sensing.

Source: TUHH 

Remote Sensing provides the unique opportunity to acquire important information on, for example, terrain elevation, land use and hydrological parameters at different spatial resolutions without the necessity for expensive field campaigns.

Source: Waterboard Zuiderzeeland (2006)

Residual risk, remaining risk

Risk that remains after the implementation of protection measures.

Source: TUHH

The risk that remains after risk management and mitigation measures have been implemented. May include, for example, damage predicted to continue to occur during flood events of greater severity that the 100 to 1 annual probability event.

Source: FLOODsite


The notion ‘resilience’ refers to the ability to recover quickly and easily. The maximum possible social and economic resilience against flooding can be afforded by a sustainable flood management. Provided the aim to protect guarantees a strategic, catchment based approach and is realised in a way, which is affordable both now and in the future.

Source: TUHH

Flood resilience measures: These allow the impact of flooding in buildings to be minimised e.g. Raised electrics and hard surfaces.

Source: FLOWS, Cambrigdeshire County Council (2006)

The ability of a system/community/society/defence to react to and recover from the damaging effect of realised hazards.

Source: FloodSite


The ability of a system to remain unchanged by external events.

Source: FloodSite

Response (in context)

The reaction of a defence or system to environmental loading or changed policy.

Source: FloodSite


Retrofitting describes the upgrading of an existing building to increase safety by adding or replacing items. This could be done by any combination of changes or adjustments incorporated in the design, construction, or alteration of individual buildings or properties. The reinforcement of structures tends the only aim to become more resistant and resilient to the forces of natural hazards. Retrofitting techniques involves flood-proofing, elevation, construction of small levees, and other modifications made to an existing building or its yard to protect it from flood damage.

Source: TUHH

Return period 

Long-term average interval of time or number of years within which an event will be equalled or exceeded.

Source: UNESCO/WMO Gloss. Hydrology (1992)

The expected (mean) time (usually in years) between the exceedence of a particular extreme threshold. Return period is traditionally used to express the frequency of occurrence of an event, although it is often misunderstood as being a probability of occurrence.

Source: FloodSite


In a larger sense risk describes the possibility that human, material, economic or environmental losses can be caused by a potentially damaging event or phenomenon. The scientific approach defines risk as the probability and extend of damage due to a particular hazard.

Risk = Probability*(exposure)*consequence.

Source: TUHH

Combination of the probability of occurrence of harm and the severity of that harm.

Source: Klijn (2004)

The probability of harmful consequences, or expected losses (deaths, injuries, property, livelihoods, economic activity disrupted or environment damaged) resulting from interactions between natural or human-induced hazards and vulnerable conditions.

Source: ISO/EC (1999)

Risk is the probability of a loss, and this depends on three elements, hazard, vulnerability and exposure.. If any of these three elements in risk increases or decreases, then risk increases or decreases respectively.

Source: Blong, 1996, citing UNESCO

Total risk can be expressed in pseudo-mathematical form as:

Risk (total) = Hazard * Elements at Risk*Vulnerability.

Source: De La Cruz-Reyna (1996)

Risk = Probability *Consequences

Source: Granger et al. (1999)

Risk is a combination of the chance of a particular event, with the impact that the event would cause if it occurred. Risk therefore has two components, the chance (or probability) of an event occurring and the impact (or consequence) associated with that event. The consequence of an event may be either desirable or undesirable. In some, but not all cases, therefore a convenient single measure of the importance of a risk is given by:

Risk = Probability × Consequence

Source: Helm (1996) 

Risk is the actual exposure of something of human value to a hazard and is often regarded as the combination of probability and loss.

Source: HR Wallingford (2002)

Risk is .Expected losses (of lives, persons injured, property damaged, and economic activity disrupted) due to a particular hazard for a given area and reference period. Based on mathematical calculations.

Source: Stenchion (1997)

Risk is a function of probability, exposure and vulnerability the probability that an event will occur and the impact (or consequence) associated with that event.

Source: UN DHA (1992)

Risk acceptance

Risk acceptance describes the willingness to tolerate a risk, whereby the acceptable risk refers to the level of loss a society or community considers acceptable given existing social, economic, political, cultural, technical and environmental conditions.

Source: TUHH

Risk analysis

A methodology to determine the nature and extent of risk by analysing potential hazards and evaluating existing conditions of vulnerability that could pose a potential threat or harm to people, property, livelihoods and the environment on which they depend.

Source: ISDR (2004)

A methodology to objectively determine risk by analysing and combining probabilities and consequences.

Source: FoodSite

Risk assessment

Risk assessment is a step in the risk management process and describes the process of evaluating adverse effects caused by a natural phenomenon. The procedure of assessing risk is based on the probability of occurrence and the extent of damage.

Source: TUHH

Comprises understanding, evaluating and interpreting the perceptions of risk and societal tolerances of risk to inform decisions and actions in the flood risk management process.

Source: FloodSite

Risk communication

Risk communication refers to how flood related information is disseminated in a community. Risk communication in general is the interactive exchange of risk-related information and opinions among risk assessors, risk managers, affected community and other interested parties. Related to flood risk, risk communication can be seen as part of a broader prevention strategy. Risk communication supports education efforts by promoting public awareness, increasing knowledge, and motivating individuals to take action to reduce their exposure to hazardous substances.

Source: TUHH

Risk management measures

Methods or measures applied to achieve the required safety.

Source: Int. Symposium Interpraevent, 1992, Bd.4, p. 57

An action that is taken to reduce either the probability of flooding or the consequences of flooding or some combination of the two.

Source: FloodSite

Risk mapping

The process of establishing the spatial extent of risk (combining information on probability and consequences). Risk mapping requires combining maps of hazards and vulnerabilities.

The results of these analyses are usually presented in the form of maps that show the magnitude and nature of the risk.

Source: FloodSite

Risk perception

Risk perception is the view of risk held by a person or group and reflects cultural and personal values, as well as experience.

Source: FloodSite

Risk reduction

The reduction of the likelihood of harm, by either reduction in the probability of a flood occurring or a reduction in the exposure or vulnerability of the receptors.

Source: FloodSite

Risk profile

The change in performance, and significance of the resulting consequences, under a range of loading conditions. In particular the sensitivity to extreme loads and degree of uncertainty about future performance.

Source: FloodSite

Risk register

An auditable record of the project risks, their consequences and significance, and proposed mitigation and management measures.

Source: FloodSite

Risk significance (in context)

The separate consideration of the magnitude of consequences and the frequency of occurrence.

Source: FloodSite


Capability to cope with external stress. A decision is robust if the choice between the alternatives is unaffected by a wide range of possible future states of nature. Robust statistics are those whose validity does not depend on close approximation to a particular distribution function and/or the level of measurement achieved.

Source: FloodSite

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