Geoscience Reference
In-Depth Information
Data-Based Mechanistic (DBM) Modelling
An approach to modelling input-output systems using
linear transfer functions, usually coupled with a nonlinear filter on the inputs. The structure of the
model is identified from the available observations [Section 4.1, Chapter 6]
Degree-Day Method
A method for predicting snowmelt as proportional to the difference between
mean daily temperature and a threshold value [Section 3.4]
Depression Storage
Water in excess of the infiltration capacity of the soil that is retained in surface
hollows before significant downslope overland flow occurs. May later infiltrate into the soil after
rainfall has ceased [Section 1.4]
Deterministic Model
Amodel that, with a set of initial and boundary conditions, has only one possible
outcome or prediction [Section 1.7]
Diffusivity
The produce of unsaturated hydraulic conductivity and the gradient of the curve relating
capillary potential to soil moisture content [Section 5.1.1; Box 5.1]
Disinformation
Used to describe observational data that might be used in calibrating a model but which
is inconsistent as a result of measurement or other errors and therefore might not be informative in
identifying a good model of the system [Section 1.8]
Dispersion
Variation in the transport of water or other quantity as a result of variation in flow velocity
within some control volume. This may be a result of variations in velocity within a particular pathway
or of variations across multiple pathways as a result of heterogeneity in the characteristics of different
pathways. The latter is often referred to as macrodispersion (see also Advection) [Sections 4.3, 11.2;
Box 11.1]
DistributedModel
Amodel that predicts values of state variables varying in space (and normally time)
[Section 1.7]
Double Mass Curve
A plot of the cumulative volumes associated with two measurement stations
(either rainfalls or discharges) [Section 3.2]
Dynamic contributing area
The area generating surface runoff that will tend to expand during a storm
[Section 1.4]
Eddy Correlation Method
A technique for measuring actual evapotranspiration and sensible heat
fluxes by integrating the rapid fluctuations in humidity and temperature associated with turbulent
eddies in the lower boundary layer [Section 3.3.3]
Effective Rainfall
A part of the storm rainfall inputs to a catchment that is equivalent in volume to the
“storm runoff” part of the hydrograph (but note that the storm runoff may not be all water from that
event) [Section 1.3, 2.2]
Effective Storage Capacity
The difference between the current moisture in the soil immediately above
the water table and saturation [Section 1.5]
Ensemble Predictions
A set of simulations based on running multiple models with different parameter
sets or initial conditions. Used in weather forecasting, climate change predictions and uncertainty
estimation [Sections 7.10, 8.2, 8.9]
Environmental Tracer
A tracer for water flow through a hillslope or catchment system that occurs
naturally in the environment. Oxygen and hydrogen isotopes are the most commonly used environ-
mental tracers because they are part of the water molecule, but other tracers are also used [Sections
11.2, 11.3, 11.8]
Ephemeral Streams
Streams that are frequently dry between storm periods [Section 1.4]
Epistemic Uncertainty
Uncertainty that is due to lack of knowledge in describing processes
or defining input and boundary conditions or to changes in the system over time [Chapter 7,
Section 12.3]
Equifinality
The concept that there may be many models of a catchment that are acceptably consistent
with the observations available [Section 1.8, 7.10]
ESMAModel
The “explicit soil moisture accounting”model (sometimes called a conceptual model). A
hydrological model made up of a series of storage elements, with simple equations to control transfers
