What does the future look like?
Australia's growing population and changing climate patterns imply that the characteristics of the floods we experience will change in the future. Better future land use planning and floodplain management can mitigate the impacts of flooding. Appropriate urban design can reduce the severity of flood impacts. Catchment and waterway revegetation can reduce the impact of flooding. Climate change is likely to affect flooding patterns. Emerging technologies can improve our ability to predict and manage floods.
Climate change will affect flooding patterns
Because flood events are influenced by a number of factors, based on the current science it is difficult to confidently state that, overall, extreme flood events in Queensland will increase in intensity or frequency as a result of climate change. However, increased coastal inundation from sea level rise and increased chance of flash flooding because of an increase in short-term heavy rainfall events both seem highly likely, based on current assessments of projected climate change.
There are four specific questions about climate change that have relevance to future flooding in Queensland:
Will the systems that drive our regional climate be affected? This question is relevant because of the strong tendency for widespread flooding to occur during La Niña events, the 'wetter' extreme of the El Niño - Southern Oscillation, ENSO (see What factors contribute to floods?) for more information). If La Niña events, or their effects on Queensland rainfall, became more frequent or more intense because of global warming, we can expect more frequent flooding. Currently it is projected that, in the future, ENSO variations may be different from those in the recent past. However, we are not currently able to project confidently what those changes will be.
Will average rainfall and short-period rainfall events change? Average rainfalls in South-East Queensland are projected to increase in summer and decrease in winter. Regarding short-period (e.g. less than 24-hour) rainfall events, the Intergovernmental Panel on Climate Change recently concluded that it was likely such heavy precipitation events would become more frequent over most land areas. This could lead to increased flood risk, especially for flash floods. A re-evaluation of probable maximum precipitation could be required, along with flood resilience capacity for critical infrastructure such as dams and bridges.
Will the sea level rise? Global warming is expected to lead to sea level rise, increasing the risk of flooding near the coast, including the lower reaches of coastal rivers.
Will changes in 'storminess' affect coastal flooding? Any increase in the frequency or intensity of storms could lead to increased storm surge risks, and this would exacerbate the increased likelihood of coastal inundation arising from projected sea level rise. However, it is very difficult at present to predict how storms might change. Current predictions are for a decrease in the global number of tropical cyclones, but with a possible increase in the intensity of the strongest cyclones and more intense rainfall.
Better land use planning and floodplain management can mitigate the impacts of flooding
The future will see Australia's population continue to grow, placing increased pressures on our waterways, many of which already experience high levels of flood risk. A growing population will result in increased development on the floodplain and the temptation to build in flood corridors. Rising land prices and a resulting move to smaller block sizes are expected to result in our cities becoming more densely populated, increasing the chance of flooding in the cities. More houses built closer together increases the number of houses potentially exposed to flood damage.
Better strategic land use planning will be essential to limit the growth of flood risk
This will require improved flood studies and floodplain management plans to enhance our understanding of how floods will behave under changing climate and catchment conditions.
Implementing the findings of these studies and management plans will help constrain development from areas where it would increase the negative impacts of floods on other properties, including the delineation of flow corridors to support the safe passage of floodwaters through urban areas. Improved flood studies and management plans would also help restrict development from areas where there would be an intolerable flood hazard to people or property, or where people could not be readily evacuated to dry land, or a practical alternative, in the case of a flood.
In areas that are deemed suitable for development, these improved flood studies and management plans can help identify the types of developments that will be suitable for specific locations and the development controls necessary to reduce any residual flood risk in these areas to an acceptable level. These controls could include minimum fill and floor levels, assessing and delineating flood evacuation routes to flood free land, designing subdivision layouts to facilitate staged evacuation and providing innovative building designs. Information from these studies can also inform regional land use planning, local environmental plans and development control plans
Figure 15: An example of detailed urban flood modelling
Future development should also be guided by detailed flood models. These models would enable all impacts of proposed new urban land uses to be quantified, and for issues such as flood evacuation strategies, the impacts of infrastructure and the need for compensatory works to be assessed. These models should also be used to assess how infill development and the increasing density of our urban environments can be managed from a flood perspective.
Appropriate urban design and integrated water management can reduce the severity of flood impacts
Historically, we have managed flooding, water supply and wastewater separately. In the future, it is highly likely that more integrated water planning will occur to better deal with Australia's flood-drought cycle, minimising human impacts on the environment, and helping manage the impacts of our growing population and changing climate on water resources and flood risks.
Further, if appropriate urban development takes place – adopting approaches such as water sensitive urban design - it may be possible to reduce some of the increases in the severity of frequent urban flood problems associated with future increased urbanisation.
Water sensitive urban design, while having little effect on larger storm events such as those that occurred recently in Queensland, has the potential to reduce the volume of local flooding in smaller storm events through the capture and reuse of water in storages such as tanks and groundwater systems. This approach is one in a suite of techniques that will enable future towns and cities to be more flood resilient.
In the future, cities and towns designed in a water sensitive manner and using integrated water planning may use less drinkable water, potentially allowing us to manage our dam water levels with more flexibility. For example, dams could potentially be operated at lower levels before predicted wet seasons, thereby providing additional flood mitigation capacity. This issue will need to be balanced with the additional pressures on water supply security from population growth.
In flood prone areas, where residents can be effectively evacuated to dry land during a flood, and where the predicted speed and depth of flooding are within accepted limits, existing dwellings could be redeveloped in the form of modified 'Queenslander' style dwellings (Figure 16)
Figure 16. Flood resilient Queenslander, designed to 'live' with flooding and incorporating water sensitive urban design techniques. Image courtesy of Cox Rayner Architects
These houses would use more appropriate flood resilient materials, which can withstand the effects of inundation and be readily cleaned after a flood, and would be designed in a way that allows household contents to be quickly moved above flood levels within the house before evacuation.
Catchment and waterway revegetation can reduce the impact of flooding
Although it is unlikely that the way we use rural land in Australia will change dramatically in the future, our understanding of how these areas should be managed to minimise their adverse effects on downstream environments, and especially on water quality, is improving. Many of these management techniques also have significant potential to help with downstream flood mitigation. One technique being piloted in the South-East Queensland region is the creation of a dense band of vegetation 30 to 50 m wide along the banks of major upper and mid-catchment waterway corridors. While these techniques appear to have merit, careful consideration needs to be given to the potentially adverse upstream flood impacts of such measures.
Emerging technologies can improve our ability to predict and manage floods
Better weather modelling and improved forecasting systems: The accuracy of weather modelling has improved substantially during the past decade. This improvement will continue as more accurate computer models are developed, and as these models are informed with better observational data. Real-time radar observation of rainfall and satellite monitoring of inundation will also improve.
As the science of weather modelling improves, we should be able to more reliably predict the near term - in the order of several days into the future - patterns and magnitudes of rainfall on our catchments. In the not-too-distant future, this should enable us to develop near real-time flood forecasting systems that link predictions of rainfall with the flow of water from our catchments and the resultant flood levels and velocities in our creeks and rivers and on our floodplains. These systems, which could potentially provide forecasts in near real time via the internet, will be able to provide flood forecasts with greater accuracy and longer lead times than today.
Better flood warning systems: The improved predictive systems described above will increasingly be linked to real-time flood warning systems. Such systems could realistically have several categories of alert that may significantly reduce damages associated with flooding by giving residents more time to prepare. Real-time flood models could be linked to interactive (internet based) maps that provide residents with detailed information on key issues such as:
- predicted peak flood levels, rates of rise for their location, and escape routes together with predictions of evacuation time and the provision of staggered 'get out' warnings to isolated residents;
- traffic network advice that assists with escape route planning to minimise congestion;
- the locations and availability of emergency centres and whether space is available.
These systems may have a simulation capability to allow disaster training and practices.
References and further reading
- Coombes, PJ, Cullen, A & Bethke, K 2011, Towards sustainable cities – integrated water cycle management (IWCM), Existing Principal Activity Centre at Doncaster Hill.
- Institution of Engineers, Australia 2006, Australian Runoff Quality: a guide to water sensitive urban design, Institution of Engineers, Australia, Canberra.
- Intergovernmental Panel on Climate Change (IPCC) 2007, Climate Change 2007: Synthesis Report, Contribution of Working Groups I, II and III to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, IPCC, Geneva.
- McLuckie, D, Kandasamy, J, Low, A & Avery, D 2010, ‘Chapter 10 – Managing risk to future development', in D McLuckie & J Kandasamy (eds), Floodplain Risk Management, University of Technology Sydney Course Notes, Sydney.
- Vecchi, GA & Wittenberg, AT 2010, ‘El Niño and our future climate: where do we stand?' Wiley Interdisciplinary Reviews: Climate Change, vol. 1, no. 2, pp. 260–270.
- Whelans, Halpern Glick Maunsell, Thompson Palmer & Murdoch University 1994, Planning and management guidelines for water sensitive urban (residential) design, consultants report prepared for the Department of Planning and Urban Development, the Water Authority of Western Australia and the Environmental Protection Authority, Whelans, Perth.
- Read the complete list of references for the Understanding Floods report