Why don’t our cities cope with heavy rain?

By  Amy Edwards ,  Sophie Schmidt 10 January 2024 5 min read

Over the last few years, Australia has experienced some extreme storms and floods that have claimed lives, resulted in property losses and caused major ecological damage.

Flooding rains (or extreme rainfall) is part of Australia’s naturally occurring climate. Our geographical location, surrounded by the Pacific, Indian and Southern oceans, makes us vulnerable to these climate systems. Our rainfall patterns vary a lot year-to-year, and decade-to-decade, thanks in part to natural drivers like the El Nino-Southern Oscillation.

But more recently, we’ve noticed a trend in the intensity of heavy rainfall events when we do receive them. And, in the future, there is likely to be more intense short-duration heavy rainfall events throughout the country.

According to the Intergovernmental Panel on Climate Change (IPCC), the projected increase in heavy rainfall will increase flood risk in cities, built-up urban areas, and small catchments, where extreme rainfall over hours to a day can quickly become flash floods. It's more complex in rural areas and for larger river basins, where floods are driven by multi-day rainfall events and by the preceding soil moisture conditions.

Our research can’t prevent extreme events from happening, but it can help protect people from the effects. 

A multi-faceted approach to flood mitigation

We have now entered the second phase of our $11.2 million Northern Rivers Resilience Initiative. It will provide future flood mitigation options for the flood-affected NSW Northern Rivers region. The first phase informed the Australian Government’s announcement in February and July 2023 of $150 million flood mitigation projects.

The Northern Rivers region covers a large area with townships, industrial and agricultural land use. Between February 23 and March 1, 2022, extreme rainfalls translated into record high stream flows, volumes and water levels in the region. Major flood levels were exceeded by more than 2 metres in several locations. This included Lismore where the flood reached a record 14.37 metres.

Meanwhile, we deployed our web-based logistics tool TraNSIT. It is used to understand the impact of high risk and extreme weather events on our supply chains across Australia. In partnership with the Australian Climate Service (ACS), the tool has supported improved decision making. We provided daily reports over the 2023-24 High Risk Weather Season and continue to do so. The daily reports capture the road closures, weather related incidents such as flooding and provide detailed information on impacted supply chains and communities.

We are also working on better city planning for storms (which can incorporate cyclones, wind damage and hail) and other extreme events.

Cities in full flood

Australian cities and suburbs are predominantly covered in artificial surfaces such as roofs, roads and pavements. Compared to rural landscapes, the impervious surfaces in urban areas increase runoff. This in turn can increase the risk of flash flooding and result in pollution of waterways with urban contaminants.

Dr Tim Muster is a Principal Research Scientist with our Cities, Consumers and Resources Team. He believes it's essential we plan our cities to better cope with extreme events such as heat, storms, wind and flooding.

"This is critically important to reduce health-risks and danger to lives, minimise property loss, and reduce any negative effects on the natural environment," Tim said.

"We do research on how to find future-ready and reliable solutions that tackle sustainability and resilience issues while not at the expense of liveability. Part of this is how our cities can be better designed, not to prevent floods, but to better cope with flood events. This could help minimise damage or losses at the community and city scale."

Water Sensitive Urban Design in our cities

In response, Water Sensitive Urban Design (WSUD) aims to increase natural infiltration of rainfall. This can help in reducing runoff and pollution of waterways, particularly from regular rainfall events. Using public open spaces and nature-based approaches to manage and restore our urban waterways will be important in slowing water flows. This helps to reduce peak floods and remove sediment and other contaminants from stormwater.

Our scientists have worked with the Goyder Institute for Water Research (the Goyder Institute) on new developments in South Australia. They wanted to test how to best apply the principles of WSUD in their stormwater management plans.

Every drop counts: what can individuals do?

Most of our research looks at large scale solutions for regional Australia as well as cities and urban areas but there are also things that residents can do individually.

At a household level, water tanks that have available capacity can also assist to take on some of the rainfall. Intense storms have the potential to fill rainwater tanks very quickly (e.g. 20 mm rainfall on 100 m2 roof can fill a 2,000-litre tank). So, it can be helpful to empty tanks in advance of predicted large rainfall events.

Previous research has shown that many people neglect regular maintenance of rainwater tanks systems. Therefore, to ensure that rainwater tanks operate as designed it is important to check before the storm that gutters and downpipes are clear of leaf litter and other debris.

Five things we can do to help prepare for storms:

1. Ensure that roads and parks are as clean as possible to reduce contaminants being washed into our waterways.
2. Encourage our yards and streets to be more permeable to water. We can use native grasses and low bushes on the edges of our creeks and streams to slow and help clean the water.
3. Naturalise our creeks and streams, including by creating floodable retention pond areas to slow down water flows.
4. Design more ways to capture and store water for later use. For example, we could store it underground in aquifers.
5. Understand that some areas in our cities will always flood and redesign them, or in some cases explore re-planning options that allow room for floods.

This article was originally published on CSIROscope in December 2017, and republished with updates February 24, 2020 and 14 December 2020 and January 2024.