Temporal features of the built environment and associations with drowning mortality: a global satellite-based...

Drowning remains a major global public health challenge. This study examined whether the timing and trajectories of urbanisation, beyond the current built environment, are associated with subnational drowning mortality.

We linked satellite-derived measures of built-environment change (Global Human Settlement Layer), population crowding (WorldPop), surface water exposure (Joint Research Centre Global Surface Water) and infrastructure proxies (Visible Infrared Imaging Radiometer Suite and Defense Meteorological Satellite Program night-time lights) to Global Burden of Disease 2021 drowning mortality estimates across 203 subnational regions in 12 countries (2006-2021; 3248 region-year observations). Temporal predictors captured recent expansion, development 'newness' (≤10-year built share), acceleration/volatility and a crowding×growth interaction. We screened predictors using Least Absolute Shrinkage and Selection Operator (10-fold cross-validation) and fitted mixed-effects models with region random intercepts. Distributed-lag models tested temporal precedence and development age and income-stratified models assessed heterogeneity.

Adding temporal predictors improved fit beyond contemporaneous built-environment measures. In adjusted models, crowding×growth was strongly positively associated with drowning mortality and a higher share of recent development was associated with higher mortality. Lag models showed a development age gradient: older built environment was most protective. Associations differed by income group, with several key coefficients reversing sign across strata.

Drowning mortality was associated with development histories as well as present-day conditions, with higher rates observed in rapidly changing, dense settings and in regions with newer built environments. Cross-context heterogeneity suggests mechanisms and prevention priorities are unlikely to be uniform.

Development timing and trajectories were associated with subnational variation in mortality beyond current built form alone. Prevention and planning should prioritise transition strategies in newly developing and rapidly densifying areas.