Geology Reference
In-Depth Information
modelling as the discipline that tries to quantitatively describe the land phase
processes of the hydrological cycle. In a general conceptualized form, a hydro-
logical model attempts to produce a desirable model response (e.g.: runoff) which
describe the physical features of the hydrological system considered on a given
forcing data (e.g.: rainfall, snow, temperature, solar radiation, evapotranspiration
and wind velocity). The model may have two types of parameters: (i) physical
parameters (which directly represent physical properties of the system and normally
these quantities are measurable e.g.: catchment area, gradient, drainage length); (ii)
process parameters (not directly measurable e.g.: depth of vadoze zone, soil depth,
water holding capacity). The outputs or model responses are dependent upon the
system de
ned by the modeller and the scope of the modelling. There are different
kinds of models available, depending on which section of the hydrological cycle is
taken as the subject of interest. Examples are, river runoff, and catchment overland
ow and
groundwater table elevation for groundwater (GW) models, extraterrestrial radiation
and surface radiations in the case of solar models and evaporation and evapo-
transpiration in case of process models.
ow,
in the case of
rainfall-runoff
(RR) models, or groundwater
1.1.1 Model Classi
cation
One can
cations in literature depending on the
different criteria of consideration. A comprehensive review of the existing and recent
hydrological models can be found in Singh and Woolhiser [
83
]. However, as per
degree of conceptualisation of the involving processes, models can be broadly
classifi-
find different types of model classi
ca-
tion is based on physically-based (white-box), conceptual (gray-box) and system
theoretic (black-box) models. White box models are deterministic in nature and are
made in a physically realistic manner, considering all internal sub processes and
physical mechanisms involved in the phenomenon of the hydrological cycle. But, in
most of the situations, practical reasons like data availability and calibration issues
force the researchers to go for simple physically based or conceptual models with
lumped representation of parameters or system [
44
]. This leads to another classifi-
ed into deterministic and stochastic models. Another meaningful classi
-
cation based on the spatial resolution at which the processes are described as: dis-
tributed, semi-distributed and lumped. The lumping could be a
“
structural lumping
”
of the study area or an
of the dominant processes of interest
[
62
]. The Sacramento soil moisture accounting (SACSMA) model of the US
National Weather Service is the best example of a successful and widely used
lumped model. In distributed models the hydrological processes are represented with
a varying degree of high resolution in space and, in most cases, the model variables
and parameters are also de
“
empirical lumping
”
ned as functions of the space and time dimensions. But in
the case of simple representation of lumped models, the hydrological system is
represented as a unit block in which the varying properties are spatially averaged.
