Patterns of behaviour that pose potential drowning risk to hikers at Yosemite National Park.

PRIMARY OBJECTIVE: To analyse patterns of departure from a popular hiking trail in Yosemite National Park, at sites where fatal drownings have occurred in the past.

METHODS: This study employed direct observation. For 32 days throughout the summer of 2013, study team members observed hikers who entered areas that brought them in close proximity to hazardous sections of the Merced River. Subject and environmental data were recorded for 1417 such approaches.

RESULTS: In 81% of our observation hours, subjects entered 'risk zones.' The median number of hikers seen near/in the river was eight per hour at the Vernal Fall footbridge, and three at the top of the waterfall. A regression analysis found that air temperature and later hike starts were positively associated, and water level was negatively associated, with the rate of river approach. Means of river access were also identified. Males, teens and people who were alone were significantly more likely to be observed entering particularly dangerous areas.

CONCLUSIONS: It is common for hikers to approach water sources during summer months, particularly as air temperatures rise. By analysing how behaviour and environmental factors co-vary, safety advocates can tailor risk reduction measures to specific settings and visitor populations.