What will be the effects on floodplains and bushland?
Large areas of bushland and floodplains can be inundated by floodwaters.
Native trees on floodplains are generally adapted to the natural cycle of floods and droughts that take place in Australia and they have lifecycles to match.
Floods can trigger dormant seeds to sprout. Similarly, insects and reptiles may come out of resting. Unfortunately floods can assist weed species during an extensive inundation, by carrying weeds on currents downstream into areas where they were not previously established.
Invasive animals may benefit in this way as well. Floods like this and worse have been happening in the Australian landscape long before human habitation.
How will plants and animals recover?
Floods have been happening in the Australian landscape long before human habitation.
The short-term, broad ecosystem effects of floods, or droughts, have long shaped Australia's biogeography.
Most native species have lifecycles that enable them to be adapted to survive the wet and dry. However, to enable animals and plants to recolonise landscapes they need refuges to retreat to during disturbances, for example, patches of vegetation and variations in topographies in the landscapes like hills.
We may expect to see shifts towards species and ecosystem types that can cope with higher rainfall and water disturbances because climate models are projecting that future extreme rainfall events are likely to be more intense (resulting in more severe flooding).
What effects will the flood events have on food production and what impact will this have on food supply?
Any weather or climatic event is never one story for all farmers, industries and regions.
Above average rainfall resulting in widespread flooding can severely impact on production. Harvests can be delayed, crops and pastures can been submerged and killed, and produce spoilt.
But there are also many farmers who can benefited from the widespread good rainfall resulting in high yields and, with successful harvest, high profits.
For example, many grain crops suffering weather-damage can return reasonable profits given good yields and high prices for feed grains.
How will the soil and moisture conditions affect the planting of the following (winter) crops?
There will be a wide range of impacts from summer floods on future crops arising from soil and water changes.
In many cases the waters will recede and soil moisture levels will return to an acceptable level for farming operations.
Underground and surface irrigation sources will likely be replenished. There will be a wide range of impacts from the floods on future crops arising from soil and water changes.
In some areas there will be waterlogging that will delay or prevent summer or winter plantings and irrigation infrastructure will need to be repaired. While in other areas the increased water availability will allow a larger dryland cropping area to be farmed in the coming season.
Farms lose massive amounts of topsoil - now settling in catchments downstream, what effect will this have on crop production in the future?
Floods will remove significant amounts of topsoil over a large area of farming land. While some parts of the landscape will lose significant amounts of topsoil (both from the flood but also from the sheet erosion as rain fell on wet soils) other areas will benefit from the depositing of new topsoil.
However, the removal of topsoil is always a loss for agricultural productivity as topsoil is the part of the soil horizon with higher levels of organic matter and nutrients and generally better structure. Also where soil has been removed from actively cropped lands, the fertiliser that has been applied by the farmer has also been washed away.
These attributes are slow to replace (if ever) and ultimately reduce yield unless higher levels of inputs are applied, particularly in the short term.
Where soil is deposited, it is not necessarily a net benefit. It does not necessarily move to farmed areas but instead clogs streams, roads, fence-lines, or buildings where the flow of water is slowed momentarily.
Erosion effects are different depending on the soil, the landscape form and the land management in place beforehand (for example, contour banks). The wide range of soil types across Australia each have their own particular management problems; while the rains and flooding have caused massive erosion, landslips and loss of nutrient-rich topsoil, the effects will be site-specific. For example the rich red clay soils of the Toowoomba range are more acid with depth.
As the more neutral surface soil is lost through erosions, farmers may need to apply extra lime and nutrients before new crops can be planted. Winter farming systems across the black and grey clay soils are based on building soil moisture from the summer rains; so there is some good news for farmers with this type of soil come the following season, as they will have almost 100 per cent soil moisture to start their next plantings.
In addition, following heavy rain farmers relying on irrigation will have replenished water supplies, in the case where dams and equipment have not been damaged. Successful farmers accurately match soil type, irrigation method and crop choice so decisions about next season’s crops and farm management practices will need to be reassessed due to the floods.