The deaths of 1,300 pilgrims during the hajj in Saudi Arabia last year underscored the urgent need to mitigate dangers posed by extreme heat, with crowd management an essential first step, analysts say.
Temperatures soared to 51.8 degrees Celsius (125 degrees Fahrenheit) in the holy city of Mecca last June as 1.8 million worshippers took part in the annual rites, one of the five pillars of Islam.
Saudi officials said 83 percent of the 1,301 recorded fatalities did not have official hajj permits and were therefore unable to access amenities meant to make the hajj more bearable, including air-conditioned tents.
It was a high-profile example of the havoc wrought by heat in 2024, which the Copernicus Climate Change Service said on Friday was the hottest year ever recorded.
The vast majority of hajj pilgrims come from abroad, and diplomats involved in their countries' responses to last year's crisis told AFP at the time that most deaths were heat-related.
While Riyadh has not detailed preparations for this year's pilgrimage - still five months away - authorities will no doubt want to avoid a repeat, said Abderrezak Bouchama of Saudi Arabia's King Abdullah International Medical Research Center.
"I think they will above all reduce the risk of illegal pilgrims," said Bouchama, who has worked with the Saudi government for more than three decades on reducing heat deaths.
"I think they've learnt their lesson, so we have to see what kind of measures they have taken for that."
Other steps to make heat less perilous, such as introducing wearable sensors to quickly detect heat stress, are long-term projects that likely won't be rolled out by June, Bouchama added.
Saudi officials did not respond to AFP's requests for comment.
The hajj takes place over five to six days, mostly outdoors.
It has seen a number of disasters over the years, including in 2015 when a stampede during the "stoning the devil" ritual in Mina killed up to 2,300 people.
Responses in the past have "typically focused on infrastructure improvements and crowd control measures", said Karim Elgendy, an associate fellow at the Chatham House think tank.
"Based on this pattern, we would expect authorities to approach the 2025 hajj with enhanced heat mitigation infrastructure and potentially stricter capacity controls."
Hajj permits are allocated to countries on a quota system and distributed to individuals by lottery.
But even for those who can obtain them, the steep costs spur many to attempt the hajj without a permit, though they risk arrest and deportation if caught.
The introduction of a general tourism visa in 2019 has made it easier for all foreigners, including permit-less pilgrims, to enter the country.
Sealing off entry points to Mecca is "very difficult", meaning Saudi authorities should expect irregular pilgrims again this year, said Umer Karim, an expert on Saudi politics at the University of Birmingham.
Saudi authorities "need to make arrangements not just for registered numbers but also for additional numbers", particularly cooling and emergency health facilities, he said.
Yet Elgendy stressed last year's deaths were the product of "an unprecedented perfect storm of environmental conditions", not just a strain on resources caused by unregistered pilgrims.
On top of high temperatures, "the summer solstice timing meant pilgrims faced maximum sun exposure during outdoor rituals", he said.
The hajj's timing is determined by the Islamic lunar calendar and will move forward about 11 days in the Gregorian calendar, meaning this year it will again fall during the scorching Saudi summer.
Authorities were pursuing heat-mitigation measures at holy sites long before last year's deaths.
Near the Kaaba, the black cubic structure in the Grand Mosque in Mecca towards which all Muslims pray, air-conditioned spaces allow pilgrims to cool off, and a climate-controlled pathway connects the hills of Safa and Marwa inside the mosque compound.
Since 2023, roads used by the faithful have been covered in a white cooling material that Saudi officials say reduces the temperature of the asphalt by 20 percent.
Volunteers also distribute water and umbrellas and offer advice to pilgrims on avoiding hyperthermia, while misting systems and air-conditioned shopping malls provide temporary relief between prayers.
"Air conditioning is the only effective measure to protect against extreme heat," said Bouchama, calling for mobile cooling units to be deployed among pilgrims.
"Drinking water helps to rehydrate, but it is not enough. You have to get out of the heat."
Even if such steps aren't in place by this year's hajj in June, they are still worth pursuing, he said.
While the pilgrimage will eventually shift to the cooler winter season, relief will be temporary.
A 2019 study published by the journal Geophysical Research Letters said because of climate change and the timing of the hajj, heat stress for pilgrims will exceed the "extreme danger threshold" from 2047 to 2052, and 2079 to 2086.