Geoscience Reference
In-Depth Information
Incommensurate
Used here to refer to variables or parameters with the same name that refer to different
quantities because of a change in scale [Sections 1.8, 7.7]
Infiltration Capacity
The limiting rate at which a soil surface can absorb rainfall - depends on factors
such as antecedent moisture content, volume of infiltrated water, presence of macropores and surface
crusting [Section 1.4; Box 5.2]
Infiltration Excess
Runoff generated by rainfall intensities exceeding the infiltration capacity of the
soil surface. May be used either at the local point scale within a catchment (when the surface runoff may
infiltrate further downslope) or at the catchment scale to represent that part of the storm hydrograph
generated by an infiltration excess mechanism [Section 1.4]
Initial Conditions
Values of storage or pressure variables required to initialise a model at the start of
a simulation period [Section 5.1]
Instrumentalism
Approach to science based on the pragmatic concept that empirical adequacy is
sufficient to justify a model or theory. In rainfall-runoff modelling, this is equivalent to saying that a
model that gives a good fit to observations in calibration should be useful in prediction, regardless of
its theoretical underpinning [Section 6.7]
Interception
Rainfall that is stored on a vegetation canopy and later evaporated back to the atmosphere
[Section 3.3.2; Box 3.2]
Inverse Method
Model calibration by adjusting parameter values to reduce the differences between
observations and predicted variables [Section 5.1.1]
Lagrangian velocity
The average velocity taken along a flow pathway by a molecule of water or solute
or particle of sediment subject to time and space variability in local flow velocities [Section 9.6]
Land Surface Parameterisation
Hydrological model used to calculate water and energy fluxes from
the land surface to the atmosphere in atmospheric circulation models [Sections 2.4, 10.4]
Lead Time
The required time for a forecast ahead of the current time in real-time flood forecasting
[Section 8.1]
Learning set
A set of observed data used in the calibration of a neural net model [Section 4.6]
Likelihood Measure
A quantitative measure of the acceptability of a particular model or parameter
set in reproducing the hydrological response being modelled [Section 7.7; Boxes 7.1, 7.2]
Linearity
A model is linear if the outputs are in direct proportion to the inputs [Section 2.2;
Boxes 2.1, 4.1]
Linear Store
A model component in which the output is directly proportional to the current storage
value. The basic building block of the general linear transfer function model and the Nash cascade
[Section 2.3; Box 4.1]
Local Optimum
A local peak in the parameter response surface where a set of parameter values gives
a better fit to the observations than all parameter sets around it, but not as good a fit as the global
optimum [Section 7.2]
Lumped Model
A model that treats the whole of a catchment as a single accounting unit and predicts
only values of variables averaged over the catchment area [Sections 1.5, 1.7]
Macropores
Large pores in the soil that may form important pathways for infiltration and redistribution
of water bypassing the soil matrix as a preferential flow. May result from soil cracking and ped
formation, root channels and animal burrows [Section 1.4]
Model Inadequacy Function
A mathematical function (usually simple in form) designed to correct
for non-random structure in a series of model residuals that would otherwise lead to biased inference
in model calibration. The simplest correction might be a constant bias or a linear trend [Section 7.3]
Monte Carlo simulation
Simulation involving multiple runs of a model using different randomly
chosen sets of parameter values [Sections 7.5, 7.6, 7.7; Box 7.3]
Network Width Function
A histogram of the number of reaches in the channel network at a given
distance from the catchment outlet. Can be used as the basis for both linear and nonlinear flow routing
algorithms [Section 2.3, 4.7.1]
