Over 1.5 million people gathered, as usual, during the annual Hajj pilgrimage to Mecca in 2024. That year the event occurred in June, when temperatures soared to 51°C in Saudi Arabia. Many people collapsed. This ultimate expression of religious devotion turned to tragedy for the at least 1,300 pilgrims who died in the scorching heat and humidity.

The Hajj is especially prone to heat risks. As with these risks in general, vulnerability is especially high for those with disabilities or low incomes. Pilgrims can expect to walk at least several miles a day , which may be especially gruelling for older visitors. This potentially once-in-a-lifetime journey can be very costly, making it necessary for many to sleep in crowded, sweltering tents, if they have shelter at all . And pilgrims lacking official Hajj visas can’t access the official cooling and health services.

But heat-related deaths are not inevitable during the Hajj. One year after this record-setting event, the Hajj again took place in June. (Its timing fluctuates each year, like Easter.) Saudi Arabia’s government had by this time poured additional money into air-conditioned shelters, misters, shaded areas, water stations and field hospitals, as well as more heavily enforcing the visa system.

In 2025, the death toll was in the hundreds rather than the thousands. One factor was the lower temperature at that year’s event, which took place earlier in June than in 2024. But observers have also credited the planning of the Saudi government for the safer conditions—though of course hundreds of fatalities are still a tragedy.

A set of guidance documents released today by the World Health Organization reiterates the broader message that planning is key to protecting people from extreme heat during mass gatherings. One takeaway is that individuals can’t be left to fend for themselves in dangerous conditions. Ultimately, safety is built through design and planning, not depending on individual action.

The three documents are long and detailed, but an overarching message is that a combination of these elements is what has the greatest impact:

  • Cooling infrastructure in critical areas
  • Drinking water
  • Logistics to limit time spent in direct sun or high heat
  • Staff training to recognize and refer people getting sick in the heat
  • Planning to adjust or cancel events when it becomes dangerous

None of this is revolutionary, yet each factor is sometimes neglected by event organizers laser-focused on maximizing profits or beefing up security. Take drinking water. Many venues ban reusable water bottles, even during heat seasons. The WHO guidance suggests that free, safe, easily accessible and well-signposted drinking water points, possibly including refillable bottles, are essential for visitors as well as staff.

After reviewing 45 years’ worth of studies on medical care at mass gatherings, the WHO authors suggest that with enough organization, the vast majority of people can be treated onsite. These kinds of considerations require setting aside time and resources well before the event to make sure that a long chain of people is prepared and authorized to act. The WHO documents call for a point person to be designated to integrate heat into the overall risk management structure needed for any responsibly run large event.

As climate change intensifies, these kinds of heat risks will become even more predictable. The solution isn’t just to avoid all big outdoor events during hot seasons (though thoughtful scheduling, as of some Summer Olympics events, can reduce risks).

“While avoiding mass gatherings during the summer may seem like a safe option, it’s not always practical—many events are culturally, socially, or economically important and planned well in advance,” Amaia Artázcoz Glaria, a WHO public health officer, has said. “Instead of cancelling, WHO recommends that all mass gatherings include a risk assessment, which should cover heat risk management. With proper measures in place—like shade, hydration stations, early warning systems, and adjusted timings—events can still be held safely, even in hot weather.”