Geoscience Reference
In-Depth Information
Basis Functions
Interpolation functions used in representing the variation of a predicted variable within
each element of a finite element solution [Box 5.3]
Bayes Equation
Equation for calculating a posterior probability given a prior probability and a like-
lihood function. Used in the GLUE methodology to calculate posterior model likelihood weights
from subjective prior weights and a likelihood measure chosen for model evaluation [Section 7.7.4;
Box 7.2]
Behavioural Simulation
A simulation that gives an acceptable reproduction of any observa-
tions available for model evaluation. Simulations that are not acceptable are nonbehavioural
[Sections 7.2.2, 7.7]
Big Leaf Assumption
The representation of a vegetation canopy in predicting evapotranspiration as if
it was a uniform surface [Box 3.1]
Black Box Model
A model that relates an input to a predicted output by a mathematical function
or functions without any attempt to describe the processes controlling the response of the system
[Sections 1.1, 4.1]
Blind Validation
Evaluation of a model using parameter values estimated before the modeller has seen
any output data [Section 5.4]
Boundary Conditions
Constraints and values of variables required to run a model for a particular flow
domain and time period. May include input variables, such as rainfall and temperatures, or constraints,
such as specifying a fixed head (Dirichlet boundary condition) or impermeable boundary (Neumann
boundary condition) or specified flux rate (Cauchy boundary condition) [Sections 1.3, 5.1]
Calibration
The process of adjusting parameter values of amodel to obtain a better fit between observed
and predicted variables. May be done manually or using an automatic calibration algorithm [Section
1.8, Chapter 7]
Canopy Resistance
An effective resistance to the transport of water vapour from leaf stomata to the
atmosphere [Section 3.3]
Celerity
or Wave Speed. The speed with which a disturbance of pressure propagates through the flow
domain. Important in the explanation of the large “old water” component of storm runoff in many
catchments. May vary greatly with different processes and with catchment wetness [Sections 1.5, 5.5;
Box 5.7]
Closure Problem
The problem of estimating boundary fluxes for a discrete calculation unit in part of
the flow domain when the appropriate relationships should be state and scale dependent [Section 9.2]
Cloud Computing
The use of methods and data storage available via the Internet without the user
having to worry about where computations are made or information is stored. These are becom-
ing increasingly sophisticated and can provide elements that can be integrated with hydrologi-
cal modelling (e.g. the use of GoogleMaps and GoogleView in visualisation of model results)
[Section 3.11]
Complementarity Approach
A method for the prediction of actual evapotranspiration based on the
idea that the greater the actual evapotranspiration rate (and therefore the ambient humidity), the lower
will be a measurement of evaporation from a free water surface or evaporation pan [Section 3.3]
Conceptual Model
A hydrological model defined in the form of mathematical equations. A simplifi-
cation of a perceptual model [Section 1.3]
Constitutive Relationships
Relationships between the current state of volume in the flow domain
and the boundary fluxes required to close mass, energy and momentum balance equations for that
volume. Should be expected to be hysteretic (dependent on the history of wetting and drying) and
scale dependent [Section 9.2.2]
Contributing area
A term used in a variety of ways in hydrology. Most often it refers to the part of
the catchment contributing either surface or subsurface storm runoff to the hydrograph [Section 1.4]
Data Assimilation
The process of using observational data to update model predictions (see also
Real-Time Forecasting and Updating) [Section 5.6]
