The Extreme Floods Which Devastated Spain Are Hitting More Often. Is Australia Ready for the Next One?

Spain recently experienced devastating floods in the Valencia region, where regions saw staggering rainfall levels, equivalent to an entire year’s worth in just a single day. Over 200 lives were tragically lost as torrents swept through urban areas. Analyses reveal that the frequency of extreme daily rainfall in this region has doubled over the past 75 years, with intensity increasing by 12%.

The World Meteorological Organization highlights a growing concern: climate change is heightening the risk of extreme flooding. This phenomenon is fueled by the fact that warmer air can retain more water vapor—approximately 7% more per degree Celsius of warming. An increase in moisture generally results in heavier rainfall, escalating the chances of severe floods.

The link between temperature and atmospheric moisture capacity has been understood for nearly two centuries. However, recent findings suggest a more dire situation. When water vapor condenses into raindrops, it releases heat, potentially intensifying storm updrafts and making rainfall even heavier. Hence, extreme rainfall could increase by over twice the rate of the initial 7% per degree of warming.

Australia recently updated its flood design guidelines in response to the changing climate. The updated guidance aims to ensure future infrastructure withstands extreme floods. However, many existing structures, like bridges and stormwater systems, remain vulnerable to surges in extreme rainfall. Moreover, current flood planning levels—dictating placement for buildings such as homes, hospitals, and offices—do not adequately address this heightened risk.

Intensifying Water Cycle

Most of us learned the basics of the water cycle in elementary school. Water evaporates, becomes rain, fills rivers and returns to oceans. Climate change is amplifying this cycle, as illustrated in a recent report by the Intergovernmental Panel on Climate Change. Rain is occurring in shorter, more intense bursts, increasing the likelihood of flooding events.

This year alone, catastrophic floods have wreaked havoc across the Americas, Asia, and Europe due to extreme storms—scientific studies have attributed their severity to human-induced climate change.

Australia’s Flood Vulnerability

Australia isn’t exempt from severe flooding. The catastrophic floods in northern New South Wales in 2022 resulted in the loss of 24 lives and led to over A$5.65 billion in damages, marking the country’s costliest natural disaster to date.

Preparing for Escalating Floods

Urban planners and engineers must consider flooding when designing new infrastructure. Traditionally, they’d refer to Australia’s flood design guidance. This document previously allowed a 5% increase in rainfall intensity per degree of global warming for long-lifespan infrastructure. But this contradicts many studies indicating more substantial increases, already evident.

A comprehensive review of over 300 scientific papers focusing on climate change and severe rainfall in Australia has helped refine flood guidance. A finding from this review suggests that rain events over 24-hour periods could increase by 8% per degree of warming, not the previously estimated 5%. Furthermore, hourly rainfall extremes might rise to 15% per degree.

Disturbingly, these findings are just estimates. The range of potential outcomes suggests that some rain events could be even more severe. For longer extreme rains, the increase might range from 2-15%. For shorter, intense rain bursts, this could be between 7-28%.

During February 2022, the Lismore region recorded about 600-800 mm of rain, vastly exceeding the usual average of around 150 mm for that month. With global temperatures having already risen by 1.1°C since the pre-industrial era, continued warming could lead to even heavier rainfalls, worsening flood risks.

The recent updates to Australia’s flood design guidance have incorporated these new findings. This advancement ensures that upcoming infrastructure projects are informed by the latest scientific understanding of climate change and flood risks. Over time, this will guide the design and construction of robust infrastructure, such as local stormwater systems, levees, bridges, and dam spillways.

Governments at local, state, and federal levels can utilize this information to set property development heights and plan emergency responses to floods.

Can We Prevent Catastrophic Floods?

The strengthened understanding and tools we now possess allow us to adapt to heightened flood risks. Nonetheless, implementing these measures isn’t without challenges. In many cases, it will necessitate retrofitting or redesigning existing systems to cope with intensified flooding.

Climate change has turned into a pressing concern, no longer a distant issue. Flood risks are already significantly higher than they were two decades ago and will continue to escalate. Rapid adaptation is crucial to mitigate the impact of extreme, sudden rainfalls and floods like those observed in Spain.