Peak discharge (syn, maximum discharge, peak flow) :
Maximum discharge for a given flood hydrograph.

Planning map :
A map (often in the form of a statutory district plan) on which prescribed or suggested land uses or planned processes are shown. It serves a prescriptive, rather than a representative, function.

Population at risk :
All those persons who would be directly exposed to the consequences of failure of a structure or facility if they did not evacuate.

Precondition factors (stability) :
Inherent factors (usually static) that are necessary but not sufficient for causing a slope to fail.

Prediction :
A statement to the effect that a particular impact will occur in a particular area, with a particular magnitude and set of effects, during a particular time interval. Predictions are the responsibility of bona fide scientists and are usually given in a probabilistic terms. The word is virtually synonymous but not as definitive as forecast.

Predictor :
A variable or index compiled from several elements, which is known (often empirically) to be highly correlated with a quantity which is to be forecast and is used to forecast it.

Preparatory factors (stability) :
Factors (usually dynamic) that reduce the margin of stability of a slope without actually causing failure. Preparedness involves the development and regular testing of warning systems (linked to forecasting systems) and plans for evacuation or other measures to be taken during a disaster alert period to minimize potential loss of life and physical damage; the education and training of officials and the population at risk; the establishment of policies, standards, organizational arrangements and operational plans to be applied following a disaster impact; the securing of resources (possibly including the stockpiling of supplies and the earmarking of funds); and the training of intervention teams. It must be supported by enabling legislation.

Preparedness :
Activities and measures taken in advance to ensure effective response to hazards and their consequences.

Prevention :
Activities to provide outright avoidance of the hazards and their consequences.

Probabilistic :
A description of procedures, which are based on the application of the laws of probability. Contrasts with deterministic.

Probability :
A measure of the degree of certainty. This measure has a value between zero (impossibility) and 1.0 (certainty). It is an estimate of the likelihood of the magnitude of the uncertain quantity, or the likelihood of the occurrence of the uncertain future event. There are two main interpretations: i) Statistical - frequency or fraction – The outcome of a repetitive experiment of some kind like flipping coins. It includes also the idea of population variability. Such a number is called an objective or relative frequent probability because it exists in the real world and is in principle measurable by doing the experiment; ii) Subjective probability (degree of belief) – Quantified measure of belief, judgement, or confidence in the likelihood of an outcome, obtained by considering all available information honestly, fairly, and with a minimum of bias. Subjective probability is affected by the state of understanding of a process, judgement regarding an evaluation, or the quality and quantity of information. It may change over time as the state of knowledge changes.

Probability density function :
A function describing the relative likelihood that a random variable will assume a particular value in contrast to taking on other values.

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