Key parameters to improve prediction of the drift and resurfacing of human bodies following drowning in rivers

Abstract. Drowning is a major global health concern, and urban rivers pose a significant risk. Climate change is leading to increasingly frequent extreme floods and heatwaves, which drive people to bathe in urban water bodies. The rapid recovery of victims is critical for their survival, as well as for investigations, and first responder safety. Recent research highlights the potential of combining hydrodynamic computer simulations with drift modelling to predict the trajectory of drowning victims’ bodies. The present study uses a unique dataset of 50 real-world fatal drowning cases to identify two key parameters needed to improve computer simulations of body drift in urban rivers: the initial body buoyancy (i.e. before the effects of decomposition) and the body submersion interval. The results reveal that older age and a higher body mass index are significantly correlated with increased initial buoyancy, due to physiological factors such as lower bone density and higher body fat content. Bodies of victims over the age of 65 are almost four times more likely to remain afloat. A temperature threshold of around 7 °C appears to limit body floatability, and lower water temperatures are associated with longer body submersion intervals due to slower decomposition. A resurfacing value of 97 °C · days was estimated for the ‘accumulated degree days’ (ADD), a criterion which has been recommended for predicting the body resurfacing time but has barely been quantified in prior studies. Additionally, older female individuals with a higher BMI were found to be significantly more likely to be victims of suicidal drowning, indicating a distinct risk profile that is important for prevention strategies. These findings emphasize the importance of incorporating empirical data into drift models and building larger, transnational databases to improve predictive accuracy and save lives.