Wimbledon recorded its hottest opening day at last year’s Championship and the heat could be a significant factor once again across the fortnight at the grand slam tournament.

The start of last year’s Wimbledon was played out in temperatures reaching 33C and brought the sight of players attempting to cool themselves with ice towels.

Extreme heat has played a part in both of this season’s grand slams, with temperatures of 46C at the Australian Open and a heatwave hitting the French Open, too.

Defending Wimbledon champion Jannik Sinner has at times struggled in the heat, and was knocked out of the French Open during a sweltering second round.

It means there is likely to be renewed focus on Wimbledon’s heat rules, as well as an eye on the upcoming forecasts at SW19.

What is Wimbledon’s heat rule?

Wimbledon has a heat rule in place for this year’s tournament and players are allowed to request a 10-minute break when the heat stress index is at or above 30.1C.

The heat stress index accounts for air temperature, humidity and surface temperature – creating a ‘feels-like’ reading that is also known as the Wet Bulb Globe Temperature [WGBT].

The heat stress index will be measured 30 minutes before the start of play, then at 2pm and then at 5pm. The 10-minute break would take place between the second and third sets for women’s singles matches and between the third and fourth sets for men’s matches.

Wimbledon states once a match has started with the heat rule in place, it cannot be lifted if the weather conditions change. It adds that the heat rule cannot be introduced for matches that were suspended overnight and are midway through.

The heat rule was triggered during Wimbledon qualifying, as London experienced an “extreme heat” red weather warning and the hottest June day on record. The high temperature may have had a part in a brief power outage at the qualifying tournament.

How does it compare to other grand slams?

The Australian Open uses a heat stress scale. A 10-minute cooling break is enforced if the scale reaches 4.0, while play was suspended at this year’s tournament when the scale reached 5.0, its highest level.

The French Open uses Wet Bulb Globe Temperature and the heat rule is enforced when it hits 30.1C, triggering a 10-minute cooling break. There is then a suspension if the WGBT reaches 32C.

Despite cramping and suffering a physical breakdown during his shock French Open defeat to Juan Manuel Cerundolo, the WGBT did not reach the threshold required to trigger a stoppage during Jannik Sinner’s exit.

Afterwards, Sinner did not blame the heat and said he felt ill earlier in the day. “It was warm, but not crazy warm,” Sinner said. “I feel like it was quite OK to play. It was nothing against the heat, nothing against the weather. It was just me today, but it happens.”

What about the fans at Wimbledon?

Wimbledon has worked to introduce more shaded areas and water points around the grounds. Fans are also advised to keep hydrated, apply sunscreen, wear light clothing and a hat, as well as taking time off court if sitting directly under the sun.

There were several instances of fans struggling in the heat last year. Both Carlos Alcaraz and Aryna Sabalenka brought water over to fans who had to receive medical attention during their matches.