Models in Irrigation andWater Management - Practices of Irrigation and On-farm Water Management - page 390

Fig. 10.2 Schematic of a
conceptual model for
irrigation

Start Model
IRRIGATION

Inputs:
- soil data - rainfall data
- crop data - water-table depth
- pan evaporation
- pan factor

Input

Irrigation interval

Output

No

Option to include
leaching fraction

Yes

Input LR or EC w and
EC e

Irrigation depth

Output

Option to calculate
for another crop

Yes

No

Stop

Sensitivity testing is an integral part of the model development process, usu-
ally accompanying the calibration/verification phases. It provides information on
the relative importance of model parameters and their influence on model response
in terms of state variables simulated. Within the period of model development, espe-
cially at the time of sensitivity analysis, it is appropriate to fix the character of the
model, i.e., to provide documentation for the user.
The real test of model performance is in application. This may reveal deficien-
cies in model, requiring appropriate modification in structure, formulation, solution
technique, parameter estimates, or basic data.

10.2.5 Model Calibration, Validation and Evaluation

The model evaluation procedure involves both calibration and validation of the
model. Before simulation models are used, they need to be calibrated and validated
for the conditions under which they will be used.