Geoscience Reference
In-Depth Information
Appendix B
Glossary of Terms
Actual Evapotranspiration
The rate of evapotranspiration from a surface or vegetation canopy to
the atmosphere under the prevailing meteorological conditions and water availability [Section 3.3;
Box 3.1]
Advection
Transport with the velocity in a flow pathway. Often used to refer to transport with the
mean velocity of the flow within some control volume (see also Dispersion) [Sections 4.3, 11.2;
Boxes 3.1, 11.1]
Aerodynamic Resistance
Scaling parameter for sensible and latent heat fluxes in Penman-Monteith
equation [Section 3.3; Box 3.1]
Aleatory Uncertainty
Uncertainty due to randomvariations that can be described by a statistical model
[Chapter 7, Section 12.3]
Antecedent Conditions
The state of wetness of a catchment prior to an event or period of simulation
[Section 1.4]
Aquiclude
A layer of soil or rock that is impermeable to water [Section 5.1.1]
Atmospheric Demand
The rate of potential evapotranspiration for given atmospheric conditions of
temperature, humidity and wind speed without any limit due to the availability of water [Section 3.3]
Autocorrelated Errors
A time series of model residuals that are not independent at each time step,
i.e. that exhibit statistical correlation at one or more time steps apart (see also Heteroscedastic Errors)
[Section 7.3; Box 7.1]
Automatic Optimisation
Calibration of model parameters using a computer algorithm to maximise
or minimise the value of an objective function [Sections 7.1, 7.4]
Baseflow
That part of the discharge hydrograph that would continue after an event if there were no
further rainfall. Sometimes taken to be equivalent to a subsurface flow contribution to stream discharge,
in which case a response during a storm might be expected, but environmental tracer measurements
suggest that this is not good usage of the term since subsurface flow may be the dominant contribution
to the hydrograph in many storms [Section 2.2]
BaseflowSeparation
Aprocedure associatedwith use of the unit hydrograph to separate the hydrograph
into “storm runoff” and “baseflow” components. Many different methods are available, mostly without
any firm basis [Box 4.2]
