Heat is changing the rules for major events. WHO wants organizers to plan before crowds arrive
New guidance makes cooling, water and medical capacity part of event operations.
A concert, pilgrimage or sporting event can become a health emergency before its organizers recognize that heat has overwhelmed the people attending it. New World Health Organization guidance puts responsibility for preventing that escalation into the planning of the event itself.
Released September 30, the guidance draws on studies from 1980 through 2025 covering nearly half a million medical encounters, including more than 22,000 heat-related illnesses. WHO says well-organized medical services can treat more than 90% of patients at event sites, reducing pressure on ambulances and hospitals.
That finding describes what effective systems can achieve. It is not a guarantee that any gathering can safely proceed at any temperature.
The agency recommends combining drinking water, cooling infrastructure, changes to schedules, crowd management, protection for workers and prepared on-site care. Transport, toilets and communications are part of the same operational problem: protection is less useful if people cannot reach it.
The scope extends beyond athletes. Spectators, volunteers and staff can spend long periods outdoors, sometimes in unfamiliar conditions, while dense crowds and travel make access to water or medical assistance harder.
Heat affects the body through more than air temperature alone. WHO's separate health guidance identifies humidity, wind, radiant heat and clothing among factors influencing whether a person can lose accumulated heat. Trying to cool the body also puts stress on the heart and kidneys.
That helps explain why an apparently modest increase in temperature may have unequal consequences. Age, underlying illness, occupation, housing and access to cooling all affect vulnerability. Outdoor workers and emergency personnel face exposures that are different from those of a spectator able to leave.
Prolonged hot days and nights add further strain. Heat can also interrupt the services needed during an emergency when electricity, transport or water infrastructure fails. Planning therefore has to account for both the number of people needing help and the reliability of the systems providing it.
WHO's established mass-gathering work places these decisions inside broader risk assessment, surveillance and emergency response. The heat guidance is intended to complement existing clinical and occupational rules, rather than replace them with a single worldwide cancellation threshold.
For organizers, the practical test is whether the plan can be implemented while the event is operating. A cooling area needs accessible routes; medical teams need communications; schedule changes need to reach ticket holders, contractors and workers.
For governments and event owners, publishing a plan is only the beginning of accountability. The useful measures include whether assistance was reachable, whether serious cases received timely care and whether local health services were overwhelmed. The guidance offers a framework for prevention, but the result depends on decisions taken before and during the gathering.
