4 Indicators
4.1 WHAT IS AN INDICATOR?
An indicator is a measure of the state of a system that enables us to evaluate the effect of our actions on resources and adjust our actions to meet specified goals. Indicators are key variables that signal change, and can be physical, chemical, biological, social or economic. They may be directly measurable or calculated from measurements of a number of data sets, or derived from other information.
Some indicators are direct and simple measures of an effect, such as the amount of irrigation water coming onto a farm, or annual wheat yield. These indicators are easy to measure and give a direct measure of water use and production. However, there are other effects that cannot be described by a simple direct indicator. One example is the amount of nitrogen leaching from a farm into groundwater. Lysimeters can be used to give a measurement of nitrogen leaching at selected points on a farm, but it is not a simple calculation to extrapolate these values to an overall farm figure. The amount of nitrogen leaching will vary depending on rainfall, soil type, crop type, irrigation depths and timing. If lysimeter measurements are used as an indicator, farmers must be provided with a way to calculate overall farm figures from the point measurements.
A further type of indicator is a derived indicator, which is used when it is either impossible or impractical to directly measure an effect. For example, soil productivity can be described by a large list of physical, chemical or biological soil characteristics that would be expensive and time-consuming to measure. Instead, a derived indicator such as earthworm population can be used to indicate soil productivity, because many of the soil health characteristics influence the earthworm population.
4.2 SELECTION CRITERIA - DESIRABLE CHARACTERISTICS FOR INDICATORS
Before selecting indicators, it is necessary to identify the rationale that is used to select the indicators, and to identify which characteristics are desirable. The criteria used to select indicators is generic (i.e. applies to all indicators), but the importance of each criteria varies depending on the sustainability goals.
The following criteria have been identified as suitable for selecting indicators:
- influenced by irrigation system design and management;
- able to be controlled by farmers;
- readily measurable;
- comparable between farms;
- scientifically valid and repeatable;
- can measure progress towards goals on a reasonable time scale;
- can be aggregated for groups of farms.
Influenced by irrigation system design and management
The indicators must describe characteristics of a farming system that can be altered by changing irrigation system design or management. The relationship between a farmer’s irrigation decisions and the indicator should be clear and well understood.
Able to be controlled by farmers
The indicators must describe an input or output which farmers have control over (e.g. quantity of irrigation water applied). Most indicators will also be influenced by factors beyond a farmer’s control, e.g. rainfall will influence crop production, and product prices will influence profit. These additional factors should also be recorded as related information and taken into account when looking at year-to-year trends in indicator values.
Readily measurable
Monitoring and recording indicators should be quick and easy and not need significant capital investment in equipment, or require specialised technical skills. The indicators should not be expensive to measure and will, where possible, use information that farmers routinely gather as part of their farm management practices, and which is not cost prohibitive.
Comparable between farms
The indicators must be able to be compared between farms and different farming sectors. For example, profit per hectare is a more comparable measure than total farm profit. There are properties of each individual farm, such as soil type, water availability or climate that influence the profit per hectare. However, if this information is recorded, comparisons can be made between similar farms and the relative sustainability of different management practices assessed.
Scientifically valid and repeatable
The indicators should be measurable with a well-documented and accepted technique to ensure repeatability and consistency across farms. The use of scientifically valid methods will also assist in providing input to future research.
Can measure progress towards goals on a reasonable time-scale
The indicators must be measurable at an appropriate frequency to assess performance against the sustainability goals. For most of the sustainability goals in Section 3.3, values will only need to be reported annually, and the year-by-year trends assessed. The water indicators may need to be measured more frequently. For example, the annual amount of water abstracted from a river is not as important to sustainability as the maximum daily abstraction rate during low river flows.
Can be aggregated for groups of farms
It should be possible to combine the selected indicators to provide composite indicators for an entire irrigation scheme, community or region. This type of overview will help determine the cumulative benefits and effects of a scheme or group of farms.
These selection criteria are used to assess the suitability of individual indicators. One indicator may be used to indicate the progress towards several sustainability goals, but none will be able to individually assess the overall sustainability of the system.
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