Geoscience Reference
In-Depth Information
Nomogram
An empirical method for estimating runoff by using a series of graphs [Section 2.1]
Nonbehavioural Simulation
see Behavioural Simulation
Nonlinear
A model is nonlinear if the outputs are not in direct proportion to the inputs but may vary
with intensity or volume of the inputs or with antecedent conditions [Box 2.1]
Nonparametric Method
A method of estimating distributions without making any assumptions about
the mathematical form of the distribution [Section 7.2.2]
Nonstationarity
A model in which the parameters are expected to change over time [Box 2.1]
Numerical Dispersion
The effect of numerical approximation in the solution of differential equations
in smoothing the pattern of a predicted variable (see Finite Difference, Finite Element Method) [Section
5.5.5; Box 11.1]
Objective Function
A measure of how well a simulation fits the available observations [Sections 1.8,
7.3; Box 7.1]
Optimisation
The process of finding a parameter set that gives the best fit of a model to the observations
available. May be done manually or using an automatic calibration algorithm [Sections 1.8, 7.4]
Overland Flow
Downslope flow of water on the surface of the soil in excess of the infiltration capacity
and depression storage capacity of the surface [Section 1.4]
Parameter
A constant that must before defined before running a model simulation [Sections 1.6, 1.8]
Parameter Space
A space defined by the ranges of feasible model parameters, with one dimension for
each parameter [Sections 1.8, 7.2]
Parsimony
The concept, sometimes known as Occam's razor, that a model should be no more complex
than necessary to predict the observations sufficiently accurately to be useful [Box 4.1]
Partial Area Model
Runoff production (by an infiltration excess mechanism) only over part of the
hillslopes (the partial area) in a catchment [Section 1.4]
Particle Tracking Models
The representation of water, solute mass, or sediments as a large number
of particles that are tracked through a hydrological system according to some rules used to represent
the flow processes [Sections 9.6, 11.12]
Pedotransfer Function
A function for predicting soil hydraulic parameters from knowledge of soil
texture and other more easily measured variables [Sections 3.8, 5.1.1; Box 5.5]
Perceptual Model
A qualitative description of the processes thought to be controlling the hydrological
response of an area [Sections 1.3, 1.4]
Phreatophytes
Plants whose roots extract water from below the water table [Section 1.4]
Pooling Group
A group of gauged catchments defined as being similar to an ungauged catchment and
used to estimate its hydrological response [Section 10.7]
Post-audit Analysis
An evaluation of predictions made of the future behaviour of a system, once the
period of predictions has actually occurred [Section 8.8]
Potential Evapotranspiration
Rate of evapotranspiration from a surface or vegetation canopy with
no limitation due to water availability (see also atmospheric demand) [Section 3.3; Box 3.1]
Preferential flow
Local concentrations of flow in the soil that may be due to the effects of macropores,
local variations in hydraulic properties or fingering of a wetting front moving into the soil profile. May
lead to rapid and deep infiltration of water bypassing much of the soil matrix (see also macropores)
[Section 1.3]
Pre-posterior prior analysis
The concept of using predicted variables from a model (with uncertainty)
to help design a programme of observations that would lead to the most effective constraint on posterior
predictive uncertainty [Section 12.7]
Procedural Model
A model represented as a computer program. May be an exact or an approximate
solution of the equations defining the conceptual model of a system [Section 1.3]
Raster Digital Elevation Model
A gridded set of elevation values at regular spacing [Section 3.7]
Rational Method
An empirical method, first used in the 19th century, for predicting peak discharges
based on catchment area and a measure of average rainfall [Section 2.1]
