IQQM Crop Demand Model

The IQQM Crop Model replicates the water requirements for a cropped area. This is a process-based model which allows you to simulate a farmer’s decision on the area to plant in each season (along with 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 configuring crop models, the first step is to specify the crops using the Crop Parameter dialog. Then, use the water user feature editor to configure the model.

Configuring generic crop settings

The Crop Parameters dialog shown in Figure 1 (accessible via  Edit » Crop Parameters...) allows you to specify crops and their associated parameters for the entire scenario. 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 various parameters.

Figure 1. Crop Parameters

To add a new crop, right click Crop Parameters and choose Add Crop from the contextual menu. Figure 2 shows the resulting dialog. Note that the default for Use Pattern is 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, 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		Refers to the crop factor pattern used. This is NOT the format used in default of growing days.
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. Daily time-step values can be entered manually or imported as a .csv file.

Figure 3. Crop Parameters, Crop, Use Pattern On

There are three parameters that can result in the water requirement being scaled up. 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. 

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

Figure 4. Crop Parameters, Crop, Irrigation Return

Three factors may also be configured at the Return Flow tab in IQQM Crop Demand Model at a Water User to apply scaling of these parameters, allowing variation for crops from one farm to another.

These factors are:

• Irrigation return factor - Allows you to scale the irrigation return parameter defined through crop parameters configuration. This factor and parameter 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 parameter defined through crop parameters 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 irrigation return; and
• On farm escape factor - Allows you to scale the on farm escape parameter defined through crop parameters 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.

Configuring crop models

Once crops have been configured, use the water user feature editor to first create an IQQM Crop model, then configure its characteristics (Figure 5).

Figure 5. IQQM crop model

The main IQQM Crop model panel (shown in Figure 6) is divided into three main sections:

• The Planted Area section broadly defines the area to be used and the proportions between the primary and secondary crops. Refer to Table 2 for information on the configurable parameters;
• The decision dates refer to the date when the area to be irrigated is calculated using a risk function. In practice, this is the date when farmers decide how much area is to be irrigated. Primary Season Decision Date refers to the day when the water user decides the area of crop(s) to plant in the primary season. This should be before the Start Date of any specified primary crop, otherwise the area initially planted will be based on the primary crop decision from the previous year. Similarly, the Secondary Season Decision Date is the day when the water user decides the area of crop(s) to plant in the secondary season. Just like the primary season, this should be before the Start Date of any specified secondary crops; and
• The Soil section defines soil inputs. There are individual stores for each crop type. Areas that are not being cropped are referred to as fallow, and are simulated using two soil layers. Fallow area occurs between cropping seasons or during the irrigation season if the maximum developed area is not planted. At the end of a cropping season, the soil moisture of the crop area and fallow areas are merged. Table 3 provides a description of the parameters. 

When there is a significant deficiency in the moisture store, the irrigation demand generated to refill the store is limited by the pump capacity. When the Use demand limiting factor of 2x E.T checkbox is enabled, the irrigation demand will be further limited by twice the evapotranspiration if it is less than the pump capacity.

Defining crops

To define a crop, choose the crop type from the drop-down menu (resulting in the dialog shown in Figure 7) and specify the parameters as shown in Table 4.

Figure 7. IQQM Crop model, Crop

Table 4. IQQMCrop Model, Crop general configuration

Targets

By default, IQQM Crop Model will target half of the Maximum Available Soil Moisture (configured in the IQQM Crop Model main panel Soil section as shown in Figure 6) for non-ponded crops and the full Maximum Available Soil Moisture plus the Minimum Ponding Level for ponded crops.  Crop targets may be added via right-clicking the crop name, as shown in Figure 8.

If the crop is ponded, both the Minimum and Maximum Ponding Level MUST be added here.  If the Minimum Ponded Level is not added and greater than zero, the crop will target half of the soil moisture depth by default as if the crop was not ponded.  The Maximum Ponded Level represents the ponding depth at which there is runoff from the crop which can join return flow, and if there is a Minimum Ponded Level configured, the Maximum Ponded Level must also be configured with value greater than or equal to the Minimum Ponded Level to work correctly.

If the crop is non-ponded, a Crop Target may be added to override the default target of half the Maximum Soil Moisture Depth. This way, different target moistures may be set for different crops within the same farm.  Otherwise all crops within the same farm (or demand model) will have the same default moisture target.

Crop Target and Minimum and Maximum Ponding Level are added as either a daily or monthly pattern and the units are millimetres.

Figure 8. IQQM Crop model, Crop Targets

OFS Reserve volume

OFS Reserve volume may also be added by right-clicking the crop name as shown in Figure 6. The OFS Reserve volume is used to satisfy crop demands during dry periods and long travel times for ordered water.  Just like Crop Target and Minimum and Maximum Ponding Level, it can be specified as either daily or monthly patterns and is defined in millimeters. The specified depth is multiplied by planted area for each crop type to determine the reserve volume required for the crop.

OFS Reserve volume configured in IQQM Crop Model will only be used if Maintain Target Reserve Volume is checked and the Water User Determined radio button is selected at the On Farm Storage.

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 9 for the dialog and Table 5 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 10 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 9. IQQM Crop Model, Rainfall

Table 5. IQQM Crop Model, Rainfall parameters

Figure 10. IQQM Crop Model, Evaporation

Return flow

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. Figure 11 shows the dialog for Return flow and Table 6 describes the configurable parameters.

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 (using the Primary and Secondary crop dialog shown in Figure 14). 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 12); and
• Median prior 6-Monthly Inflow - Long term median 6-monthly inflows are entered as a monthly pattern (Figure 13). Note that the value for each month represents median sum of 6 months of flows for the prior 6 months in megalitres.  The index uses the value for the prior month up until day 14 of the month and then uses the current month for days after that, therefore the values entered here should be the sum for 6 months inflows inclusive of the current month.

The volume based risk function uses an inflow index based on the supplied time series data and monthly pattern. The index compares the total inflow from the time series file in the preceding 183 day period, to the long term median prior 6-monthly inflow from the supplied pattern for the preceding month for the first 14 days of each month, and the current month for the remainder of the month.

Figure 13. IQQM Crop Model, Risk functions, Median prior 6-Monthly inflow

Figure 14. IQQM Crop Model, Risk Functions, Primary Crop