Risk Management and Rainfall


Rainfall is clearly a key driver of agricultural productivity. Depending upon the timescales that are important to operations, there are a variety of tools that can be of use. In short timescales radar rainfall images provide current intensity and coverage in your local area. Climate maps give an indication of recent and long term rainfall, and hence the likelihood that there is sufficient soil moisture or dam water available for your needs. Weather forecasts provide the short term outlook needed to plan the week ahead, and seasonal information on rainfall enables a longer term plan to be laid out. Of course climate change may well determine the future direction of farming operations in Australia over the coming century. Managing risk, at all timescales, is one of the keys to a successful enterprise.

Rainfall variability and local climate

Rainfall is often described by meteorologists as a very noisy phenomenon. In other words, it can vary a great deal not only on very short timescales, but also over very small distances. For instance, a thunderstorm may deluge one location for a few minutes then cease abruptly, while just next door they receive no rainfall whatsoever. Over large parts of Australia, we also know that seasonal rainfall can vary greatly from one year to the next due to climate drivers such as El Niño and La Niña.

With such great variability in rainfall, it is worth becoming familiar with the local characteristics of rainfall at your own location.  Average annual rainfall can vary over quite short distances due to a variety of local factors, for instance the nearby topography and distance from the sea. Decisions such as the range of possible crop choice may be influenced by studying such detailed information.

Average annual rainfall (millimetres) on the Fleurieu Peninsula south of Adelaide, showing local variation due to presence of hills and proximity to the sea. The shaded square is 10 km by 10 km in size for purposes of illustration. Source: Bureau of Meteorology and 'Farming a Sunburnt Country'.

Such variability in rainfall means there are many and varied associated risks (as well as opportunities). These risks can range from those associated with local flooding to long term drought, and in turn, each has its own coping strategies.

Some typical rainfall events and episodes

Some typical rainfall events and episodes and associated rainfall type, risks and opportunities are described below. Also shown are sources of real-time information for these events.

Cold Fronts

Rainfall type and typical season of occurrence Often long bands of steady rainfall lasting less than a few hours; sometimes followed by cold showery rain. Northern end of frontal band usually gives less rain than the thicker middle region of the front.
Risks Short-lived localised flooding
Opportunities Maximise planting opportunity,
Timing of haymaking.
Increased effectiveness of superphosphate spreading.
Possible climate change risks and opportunities Possibly fewer cold fronts penetrating well inland

Cold Fronts
Weather forecasts
Rainfall outlooks
Satellite loops

Mid-latitude low pressure systems

Rainfall type and typical season of occurrence Mostly occur only on southern coastal regions.  Can give consistent long-lived light to moderate falls or heavier flooding rains, depending on intensity of low pressure and speed of travel (slower travel usually equates to more rainfall)
Risks Heavy flooding
Opportunities Rains to fill dams and soil profile
Autumn break
Possible climate change risks and opportunities Fewer systems but occasionally more intense
Information Cut-off Lows
East Coast Lows
Weather forecasts
Synoptic charts
Rainfall outlooks

The Australian Monsoon

Rainfall type and typical season of occurrence Broad areas of cloud and rain, including thunderstorms and patchy heavy showers.
Occur across northern Australia in summer, and occasionally extend further south. Can provide the impetus for significant rainfall in southern parts

Thunderstorms, lightning. 
Flooding, wind damage and storm surge associated with tropical cyclones, weed growth in winter cropping regions
In some years, e.g., El Niño years, trough may not be well developed or stay further north, producing less rainfall than in other years

Opportunities Pastoral and summer cropping opportunities
Possible climate change risks and opportunities Not well understood but possibly more variability

The Australian Monsoon
Weekly tropical statement
Rainfall pages
Satellite images
Maps of cloudiness
Experimental RMM index

Madden-Julian Oscillation (MJO)

Rainfall type and typical season of occurrence Broad areas of active and inactive tropical rainfall, particularly during summer, tracking from the Indian Ocean eastward across Australia to the western Pacific Ocean. Not a reliable indicator of rainfall over the continent, but can sometimes lead to good falls particularly in northern and parts of eastern Australia.
Risks MJO, while occasionally producing very good rains, is somewhat erratic in the rain that occurs over the continent.
Opportunities One of the main triggers of rainfall during the wet season (may give several rain episodes during a single wet season.) Research on the MJO provides potential for better tropical seasonal and intra-seasonal forecasting.
Possible climate change risks and opportunities Impact of climate change on MJO not well understood

Madden-Julian Oscillation (MJO)
Weekly tropical statement
Rainfall pages
Satellite imagery
Maps of cloudiness
Experimental RMM index

North-west cloud band

Rainfall type and typical season of occurrence More often in the cooler seasons; long band of cloud often tracking from NW Australia towards the southeast. Some of these cloud bands give good soaking rains
Risks Possible short-term flooding
Opportunities Good opportunities for rainfall through the centre of the continent, as well as through parts of SE Australia
Possible climate change risks and opportunities Climate change impact on frequency not well understood

North-west cloud band
Satellite images
Weekly rainfall statement

Monthly, seasonal and annual total rainfall

Rainfall type and typical season of occurrence The sum of rainfall from the various events occurring at a location. Rainfall may be highly seasonal or more uniform through the year depending on geographic location
Risks Long term dry conditions during unfavourable years; possibly flooding in La Niña events for some locations
Opportunities Chance to make significant profits in more favourable years
Possible climate change risks and opportunities Enhanced likelihood for drier conditions particularly south of the tropics

Seasonal climate outlook
ENSO Wrap Up
Past climate maps
Annual summaries
Climate change maps and graphs

Examples of risk analysis and decision points

Rainfall exhibits variability on all timescales, from minutes through to years and beyond. This variability produces patterns which can affect a broard range of farm operations, such as:

  • dry spells lasting days enabling in-field operations;
  • daily rainfall sufficient to suspend irrigation;
  • flash flooding lasting a few hours;
  • widespread flooding taking days or weeks to dissipate;
  • showery type weather interrupting some operations and minor irritation for tactical planning purposes;
  • regular rains of a good season providing good soil moisture;
  • deficient rains of a poor season or year leading to soil moisture and general water stress.

There are a number of techniques available to assist decision-making in uncertain environments and where information about the future is not given in an exact format but rather as a likelihood or probability. One simple and easy to use technique is the decision tree. The decision tree starts with the decision to be made, branches or boxes are added containing various options and further branching explores costs, benefits or consequences of these options in order to assist the choice of a reasonable and preferable option.


Additional Reading

Weather Derivatives

Managing Climate Variability site

This page is produced with the support of Managing Climate Variability - a consortium of primary industry research and development corporations.