Evaluating the danger posed by rip currents using a quantitative risk metric

Rip currents are some of the deadliest beachfront hazards, claiming the lives of dozens of people every year. Since rip currents are mostly invisibile, swimmers might not be aware of the risk until they find themselves caught in one. Instead, beachgoers must rely on authorities effectively conveying the danger of the water.

Xu et al. developed a risk assessment method for rip currents on rhythmic beaches — beaches with periodic features like cusps or regularly placed breakwaters — using a two-step numerical approach. They used data from this method to develop a rip hazard index (RHI) to evaluate and convey the potential danger of any given beach.

“Current risk assessment methods lacked comprehensive considerations of the rip velocities, areas, and circulation patterns,” said author Hongli Ge. “By combining linear and nonlinear models, we aimed to provide a more accurate and quantitative hazard evaluation method to improve safety and inform mitigation strategies.”

The authors first developed a linear instability model to generate different types of rhythmic beaches, before implementing a nonlinear wave model to simulate rip currents. They then used the information from this model to create the RHI, a number calculated using the current velocity, range, and circulation regime.

They next plan to expand their analysis to other types of coasts and incorporate real-time forecasting for dynamic risk alerts.

“The goal is to transition the RHI method from research to operational use in coastal safety programs globally,” said Ge. “Future applications could include integrating the RHI into early warning systems and global beach safety standards, reducing drowning incidents worldwide.”

And for swimmers who find themselves caught in a rip current, the best advice is to stay calm and swim parallel to the shore.

Source: “Risk assessments of rip current hazards on typical rhythmic beaches,” by Jie Xu, Hongli Ge, Zhongbo Liu, Sheng Yan, Kezhao Fang, Hong Jin, and Zaijin You, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0280795 .