IQQM Crop Demand Model 2

The IQQM CropMod2 replicates the water requirements for a cropped area. This is a process-based model which allows you simulate a farmer’s decision on the area to plant in each season and evapotranspiration of the different crop types, and generates a demand based on the maintenance of a target soil moisture level. You can also simulate rice irrigation by specifying ponding behaviour and return flows.

When working with crop models, first configure crops using the Crop Parameter dialog. Then, use the water user feature editor to configure the remaining parameters.

Configuring generic crop settings

Before configuring an IQQM CropMod2 Demand model on a Water User node, you must specify crops and their associated parameters for the entire scenario using Edit » Crop Parameters... (Figure 1). Crop parameters defined in this way are accessible for each water user node. This dialog is used to add crops (which can be imported via a .xml file), delete crops, and specify parameters.

Figure 1. Crop Parameters

Figure 2 shows the dialog when a new crop is created. Note that Use Pattern is toggled to OFF. Table 1 describes the parameters used in this dialog.

The method for defining crop parameters is based on FAO 56 which divides the growth period of every crop into four developmental stages based generally on water requirements. These stages are:

• Initial (or establishment) stage - occurs between planting and when there is approximately 10% ground cover. Water requirements are quite low and constant;
• Crop development (or vegetative) stage - sees a rapid increase in the amount of water required by the crop until there is generally about 70% to 80% ground cover and maximum rooting depth is achieved;
• Mid-season (or flowering) stage - requires the maximum amount of water in the life of the crop; and
• Late (or yield and/or ripening) stage - there is an approximate halving of water requirement as the crop ripens, reaches maturity and is harvested.

Figure 2. Crop Parameters, Default crop, Use Pattern Off

Parameter	Type	Description
Repeats	integer	The growth pattern and duration is repeated by the specified number. For example a growth season of 5 months when repeated by a factor of 3 will have a growth period of 15 months.
Use Pattern		When toggled to ON,
Is Ponded		When toggled to ON, the crop mix in the water user node for this crop type requires input for targets for minimum and maximum pond level. Levels are used as targets to irrigate and drain area as occurs for rice.
Coefficient		Coefficients that define the straight lines connecting the four growth stages for the crop water requirements
Initial		Coefficient at start of the initial phase
Development		Coefficient at end of the initial phase and start of development phase
Mid-Season		Coefficient at end of the development phase and start of Mid-Season phase
Late-season		Coefficient at end of the Mid-Season phase and start of Late-Season phase
Maturity		Coefficient at end of the Late-Season phase
Growing days	days	Number of days within each stage of crop growth.

Figure 3 shows the dialog when Use Pattern is toggled to ON. In this configuration, the daily time-step values can be entered manually or imported as a .csv file.

Figure 3. Crop Parameters, Crop, Use Pattern On

Figure 4 shows the dialog for the Irrigation return that can be configured for a crop. This dialog is similar for On Farm Loss and On Farm Escape.

Figure 4. Crop Parameters, Crop, Irrigation Return

Configuring crop models

Once crops have been configured, use the water user feature editor to configure characteristics of the IQQM crop model. Figure 5 shows the parameters that can be configured for the model.

Figure 5. IQQM crop model

The main IQQM Crop model panel (shown in Figure 6) is divided into three main sections. Parameters for each of these sections is outlined in Tables 2 and 3.

Climate

The IQQM Crop Model defines three parameters for climatic data:

• Rainfall - The model uses rainfall data to replenish soil moisture. Excess runoff can be re-used by the water user node. Rainfall may be input as monthly averages or daily data entered as a constant value, a time series, or as a function. Refer to Figure 7 for the dialog and Table 4 for parameter details.
• Evaporation - The model uses pan evaporation with crop factors to calculate evapotranspiration volumes. Pan evaporation is input as a time series. Refer to Figure 8 for the dialog; and
• Average daily evaporation - Enter average daily pattern for reference crop evapotranspiration. The daily average is used to forecast crop demand. If no average evap data is added then an average for each day of the year (ie. 365 day pattern) is derived from the time series data.

Figure 7. IQQM Crop Model, Rainfall

Table 4. IQQM Crop Model, Rainfall parameters

Figure 8. IQQM Crop Model, Evaporation

Risk functions

At the start of an irrigation season, each water user node decides on how much area is to be planted (and thus irrigated). This is determined by the Decision Date for the primary and secondary season. This calculation uses a relationship referred to as the farmer’s risk function. In the IQQM crop model, farmer’s risk is modelled in two different ways: an area-based approach and a volume-based one. For the former, the function relates available resource to planted area. For the latter, the function relates current the available resource to expected available resource. The expected available resource is then divided by the calculated average crop requirement to determine the planted area. Refer to the Source Scientific Reference Guide for more information.

For both area and volume based risk functions, you must specify the wet, average and dry periods (in the dialog shown in Figure 11). The model interpolates between these values based on an index of current conditions. For the area based method, the model automatically calculates the index based on soil moisture. For the volume based method, the index is calculated based on the defined inflow data as follows:

• Inflow time series - If the Risk Function type is volume, specify inflow as a constant value, a time series data or as a function (Figure 9); or
• Median prior 6-Monthly Inflow - Long term average inflows are entered as a monthly time-step (Figure 10). The volume based risk function uses an inflow inde,x based on the supplied time series data. The index compares the total inflow from the time series file in the preceding 183 day period to the long term average for the same period.

Figure 10. IQQM Crop Model, Risk functions, Median prior 6-Monthly inflow

Efficiency tab

This describes a number of parameters that can result in the water requirement being scaled up (Figure 8). Additional extractions are required if there is a practice of applying excess irrigation, with the excess being captured and returned to the water user storage. Additional extractions are also required if losses occur prior to delivery of extractions to the crop. The water user efficiency tab then allows these values to be scaled down. The default crop configuration values are zero, and hence if not defined, changing the water user efficiency parameters will have no effect.

The parameters are:

• Irrigation return factor - Allows you to scale the on farm return factor defined through crop configuration. These two parameters combined, result in an increase in the volume ordered with the additional volume being available for returning to the water user storage;
• On farm loss factor - Allows you to scale the on farm loss factor defined through crop configuration. On-farm loss represents the percentage of water that is diverted from the river and passes the irrigators meter, but doesn’t make it to the cropped area and doesn’t reappear at any other point. An on farm loss will result in the volume ordered being increased and is applied after the irrigation return factor; and
• On farm escape factor - Allows you to scale the on farm escape factor defined through crop configuration. On-farm escape represents the percentage of diversions that is lost prior to being applied to crops however this flow returns to the river system at a confluence node. An on farm escape will result in the volume ordered being increased and is applied after the irrigation return factor and the on farm loss factor.

Return flow tab

Return drainage water is surplus drainage water from irrigation or from rainfall runoff. This water can be redirected into the on farm storage or otherwise can be returned to the river via a confluence node. This is shown in Figure 9. The various parameters are shown in Table 6.

Crop mix tab

This tab (Figure 10) defines the proportions and timings of different crops planted in the defined area.