Scientists Call for a Revolution in Flood Risk Modelling
Flooding is no longer just an occasional disaster; it’s becoming a chronic, global issue. The rapid increase in flood-related damages, disruptions, and losses demands more precise tools for predicting and mitigating risks. However, scientists argue that we’re still using outdated methods that paint an incomplete picture of the threats at hand.
In a compelling commentary published in Earth’s Future, researchers from the University of California, Irvine, and the University of Bristol are urging the scientific community to ditch “bathtub modelling” in favour of dynamic, physics-based alternatives. This shift could transform our understanding of flood risks and prevent misleading narratives from spreading in the media.
The Problem with ‘Bathtub Modelling’
At its core, bathtub modelling assumes that floodwaters spread uniformly, like water filling a flat tub. While simple and visually intuitive, this approach overlooks the complexities of real-world flooding. It often misses critical factors like storm drains, levees, tidal dynamics, and groundwater systems, leading to skewed predictions.
“Bathtub models can both overpredict and underpredict flooding,” explained Brett Sanders, a civil and environmental engineering professor at UC Irvine. “One of the biggest causes of error is that these models fail to account for the systems in place to protect people and assets, such as levees and pumping stations.”
For instance, these models neglect how friction, event dynamics, and tidal amplification can shape flood behaviour. Moreover, they fail to consider how rising groundwater or pumping systems influence inundation patterns. It’s like trying to navigate a stormy sea with an outdated map—you’re bound to end up lost.
The Science Speaks
If there’s one thing scientists agree on, it’s the importance of accuracy. A model’s credibility hinges on its ability to mirror real-world conditions. According to Sanders and his team, bathtub models consistently score below 0.5 on the Critical Success Index (CSI)—a far cry from the 0.65 threshold needed for local relevance.
“CSIs under 0.5 indicate that these models are worse than a random classification,” noted Oliver Wing, chief scientific officer at Fathom and honorary research fellow at the University of Bristol. “In other words, a chimpanzee has more skill than a bathtub model in delineating flood hazard areas.”
This dismal performance isn’t just a technical issue; it has real-world consequences. Inaccurate maps can lead to misguided policies, wasted resources, and scepticism among communities that need to prepare for future risks.
Misleading Visuals and Media Narratives
The allure of dramatic visuals often outweighs the need for scientific accuracy. Short-format journal articles frequently rely on bathtub modelling, creating attention-grabbing but overly simplified depictions of submerged cities. While these images might spark concern, they rarely convey the nuances of flood risk.
“Accurate maps of areas at risk of flooding are of paramount importance for everyone—from home and business owners to insurers, banks, and governments,” emphasised Paul Bates, a professor of hydrology at the University of Bristol. “We all have a role to play in reducing flood losses, but it all starts with trustworthy information.”
When sensationalised media narratives overshadow scientific precision, public trust erodes. Residents in flood-prone areas may disregard projections that don’t align with their lived experiences, stalling critical adaptation efforts.
The Case for Dynamical Modelling
So, what’s the alternative? The researchers advocate for dynamical modelling—a more advanced approach that solves complex, physics-based equations to simulate flood behaviour. Unlike bathtub models, these methods incorporate:
- Flood attenuation: How friction and event dynamics influence water spread.
- Tidal amplification: The resonance of ocean tides within coastal areas.
- Flood defences: The role of levees, floodwalls, and pumping systems.
- Groundwater dynamics: Rising groundwater levels and their interaction with sea levels.
- Shoaling: How groundwater surfaces in response to hydrological changes.
By accounting for these factors, dynamical models provide a far more realistic and actionable understanding of flood risks.
Why Accuracy Matters
The implications of reliable flood models extend far beyond academia. Accurate projections inform everything from urban planning and insurance rates to government policies and community preparedness. They’re the foundation of effective mitigation strategies.
“Projections of flooding need to make sense to people,” Sanders stressed. “Not only for building understanding of what’s at risk but also for deciding upon the investments and policies that will be made to manage it.”
Without accurate data, we risk maladaptation—poorly designed solutions that could exacerbate the very problems they aim to solve. Trustworthy models are essential for fostering collaboration between scientists, policymakers, and local communities.
A Call to Action
The researchers’ plea is clear: It’s time for the climate science community to embrace modern tools and move beyond the outdated assumptions of bathtub modelling. With flooding projected to worsen due to climate change, there’s no room for complacency.
This work was supported by the U.S. National Science Foundation, the National Oceanic and Atmospheric Administration, and the UK’s Natural Environment Research Council. Their findings serve as a rallying cry for innovation in flood risk modelling, highlighting the urgent need for more nuanced and reliable approaches.
Turning the Tide with Better Modelling
Flooding is an inevitable part of our changing climate, but our response doesn’t have to be reactive or short-sighted. By adopting advanced modelling techniques, we can equip ourselves with the tools needed to protect lives, property, and livelihoods.
The path forward is clear: embrace complexity, demand accuracy, and prioritise collaboration. Only then can we turn the tide on this growing global challenge.
