Flooding is Not Like Filling a Bath

• Published in: Earth's future 2024-12, Vol.12 (12), p.n/a
• Main Authors: Sanders, Brett F., Wing, Oliver E. J., Bates, Paul D.
• Format: Article
• Language: English
• Subjects: Approximation; Bias; Boundary conditions; Budgets; Coastal processes; Drainage; Environmental risk; Estimates; Flood control; Flood damage; Flood hazards; Flood management; Flood predictions; Flood risk; Flooding; Floodplains; Floods; Groundwater; Hydraulics; Impact analysis; Infrastructure; Modelling; News media; Physics; Public safety; Safety management; Scale models; Sea level; Software; Topography; Uncertainty analysis
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2024EF005164

Damage and disruption from flooding have rapidly escalated over recent decades. Knowing who and what is at risk, how these risks are changing, and what is driving these changes is of immense importance to flood management and policy. Accurate predictions of flood risk are also critical to public safety. However, many high‐profile research studies reporting risks at national and global scales rely upon a significant oversimplification of how floods behave—as a level pool—an approach known as bathtub modeling that is avoided in flood management practice due to known biases (e.g., >200% error in flood area) compared to physics‐based modeling. With publicity by news media, findings that would likely not be trusted by flood management professionals are thus widely communicated to policy makers and the public, scientific credibility is put at risk, and maladaptation becomes more likely. Here, we call upon researchers to abandon the practice of bathtub modeling in flood risk studies, and for those involved in the peer‐review process to ensure the conclusions of impact analyses are consistent with the limitations of the assumed flood physics. We document biases and uncertainties from bathtub modeling in both coastal and inland geographies, and we present examples of physics‐based modeling approaches suited to large‐scale applications. Reducing biases and uncertainties in flood hazard estimates will sharpen scientific understanding of changing risks, better serve the needs of policy makers, enable news media to more objectively report present and future risks to the public, and better inform adaptation planning. Plain Language Summary Numerous studies of flood risks under climate change, such as changing sea levels and flood hydrology, assess exposure by assuming that projected water levels for oceans and rivers extend horizontally across the land surface. However, this represents a significant over‐simplification of flooding that can strongly bias estimates of flood exposure (e.g., a factor of two error). Of particular concern is that biased results sometimes feed into climate hype from the news media, which can undermine public trust in climate science. Data and models suited to more complete modeling of flooding are presented. Key Points Estimates of flood risks can be strongly biased by bathtub hazard modeling Physics‐based modeling reduces flood risk bias compared to bathtub modeling and is now feasible globally Short‐format, high‐impact journals have contribu