Irrigator operates on a daily basis generating demands and extracting water to meet these demands via the water user and supply nodes. Irrigator maintains a daily water balance for each cropping area during its planting season, to calculate the daily soil water deficit and an irrigation requirement. The irrigation requirements are used by the Water User to generate orders and opportunistic requests and to subsequently place orders and requests and to extract water from a water source.The model can be applied in both regulated and unregulated systems.
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- Evapotranspiration - defined in FAO56 as the amount of transpiration that would occur from a reference crop. Procedures for calculating evapotranspiration are documented in FAO56. In addition, the BOM and SILO climate products produce daily estimates for FAO56. Alternatively, pan evapotranspiration and pan factors can be used to define evapotranspiration;
- Average evapotranspiration (Figure 3) - used when forecasting orders. Two Theww options are provided for specifying the average evapotranspiration. You can enter a daily pattern of average evapotranspiration, specify an expression, or you can select to calculate an average evapotranspiration runtime, where the average is calculated as a rolling average of the number of previous model time-steps specified. A value of 14 days would be a good first estimate; and
- Rainfall and average rainfall are used to specify the actual forecast rainfall.
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- Yield factor - represents the Yield response factor, as expressed in equation 90 of FAO56. This parameter defines how yiel is reduced as a result of water stress. It is used in the calculation of the relative yield daily time series. Note that in Irrigation, the yield response factor is entered as a percentage rather than as a fraction;
- Expected Usage - this is a depth measured in mm (note that 100mm is equivalent to 1ML/ha); and
- Productivity - allows you to multiply the relative yield by a productivity term (eg. $/ha or tonnes/ha) to calculate socio-economic outputs.
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Figure 5 - Irrigation demand model (Crop Economics)
Runoff
The supply escape efficiency defines the amount of applied irrigation water that becomes runoff. A value of 0 results in no irrigation runoff; 10% indicates that 10% of the applied irrigation water becomes runoff. You must also specify a return efficiency, which means that the proportion of runoff that is returned to the water user can be stored in the farm storage or returned to the river. By default, both are set to 0 and do not need to be configured.
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