Flooding is complex. Factors such as climate variability, soil saturation, loss of vegetation cover in key parts of catchments, the growth of urban areas and their hard surfaces, the failure of early-warning systems, the erosion of community self-reliance and inadequate governance all influence the risks.
Complex unpredictable conditions call for an integrated suite of responses to manage the risk.
These strategies often require land to be rezoned and buildings removed. That’s a brave move in the face of urban growth pressures.
But these strategies also offer an opportunity to refocus cities, towns or even regions, by reintegrating nature and opening up new spaces for recreation, environmental regeneration and biodiversity.
Elsewhere, early-warning systems are drawing on citizen science to make communities less vulnerable.
Houses in flood-prone areas can be modified to cope with floodwaters. Typical measures include raising them on stilts and retrofitting interiors using materials that don’t absorb water. They can then be hosed down during clean-up.
Governments can provide support to minimise vulnerability. This might include funding neighbourhood resources such as boats with motors, kayaks and floodproof containers to store valuables. Water and power can be provided to designated local evacuation areas on high ground.
If all else fails, there is always managed retreat. This involves relocating a town to high ground.
Recent research reviewing all known cases of managed retreat in the United States over the past 140 years suggests this approach has had mixed results. It’s enormously expensive and exhausting. Typically, the shift benefits developers and government rather than the vulnerable communities.
If communities are to move, another study suggests the move needs to be planned well in advance. It should be done outside the time frame of a flood event when affected communities are already vulnerable.
A good way to improve flood readiness is to understand how floods work, and then to examine adaptive solutions developed by communities facing similar situations in other countries. Every river behaves differently and responses should site-specific. However, the following approaches may be relevant to local conditions and are likely to improve flood protection.
Many effective “nature-based” solutions run counter to traditional engineering works. For example, rather than engineer a river channel to make water move more quickly through an area, nature-based solutions modify or multiply river channels to accommodate variable water volumes. These approaches spread out and slow the flow of water and encourage it to soak into the ground before reaching the river.
Agricultural practices that improve soil quality, prevent erosion, slow runoff and encourage water to soak into the ground include strip cropping – alternating rows of two or more crops – to redirect and dissipate floodwaters, gully planting, and fencing and planting riverbanks.
China makes “sponge cities” with urban wetlands and revegetated waterways.
The Netherlands has removed dykes and widened river corridors as part of its "Room for the River" program.
In the Tisza Valley in Hungary, farmland has been adapted as slow-release wet-season reservoirs.
The 2022 New South Wales (Australia) Flood Inquiry called for floodplains to be thought of as assets serving environmental, recreational and community uses while allowing space for flooding.
In Jakarta, a low-lying city that regularly floods, Indonesian researchers capitalised on the intensity of flood-related social media posts. They developed an app to integrate and geolocate those posts across the catchment. The app gives residents access to alternative real-time data, allowing them to make their own decisions about timely preparation and evacuation.
Engineered infrastructure, such as dams and levees, has encouraged us to live on floodplains with little regard for the impacts of climate variability. Dams and levees work within predicted parameters, but we can’t expect that predictability anymore.