Vatican City | Pope Francis plans to head to Portugal on Wednesday to open the first post-pandemic edition of World Youth Day, hoping to inspire the next generation of Catholics while coping with the church's ongoing clergy sexual abuse scandal.

More than 1 million young people from around the world were expected to attend the gathering in Lisbon, which takes place over several days.

Busloads of pilgrims started arriving before Tuesday despite temperatures forecast to hit 35 degrees Celsius (95 degrees Fahrenheit) by the weekend's final papal Mass.

“Stay hydrated!” read a slogan promoted by the Portugal's General Directorate for Health for the event. Portuguese Prime Minister Antonio Costa advised youth day volunteers Monday to keep with them “a lot of water, because it's very hot, and a hat.” Cardinal-elect Americo Aguiar, a Lisbon bishop who is organising the festival, said two years of COVID-19 lockdowns made this year's edition of World Youth Day unique.

He said it was an important encounter for Catholic youths, especially with war raging now in Europe and economic uncertainties around the globe.

“The pope always says this event is the joy and the possibility of coming together, of the culture of coming together,” Aguiar said in an interview.

“After such limitations and difficulties, young people from all over the world will be able to meet again, with certain freedom.” Francis arrives Wednesday and is scheduled to spend the morning meeting with Portuguese officials at the Belem National Palace, the official presidential residence west of Lisbon, from where Portugal's maritime explorers of the 15th and 16th centuries set sail.

In the afternoon, Francis makes his way to the 16th century Jeronimos Monastery and church, arguably Portugal's greatest monument.

There, he is set to meet with the Portuguese Catholic hierarchy, which recently began the process of reckoning with its legacy of clergy sexual abuse.

Francis is widely expected to meet in private with abuse survivors this week and could well refer to the problem in his public remarks, as he has done during past foreign trips.

Portuguese bishops were widely criticised for their initial response to the findings of an independent commission, which reported in February that at least 4,815 boys and girls were abused in the country since 1950, most of them ages 10-14.

The bishops long insisted there were only a handful of cases, and they initially balked at suspending active members of the clergy who were named in the commission's report.

They also flip-flopped on paying reparations to victims, at first insisting they would only pay if ordered to by court rulings.

The Portuguese Catholic Church also promised in March to build a memorial to victims that would be unveiled during World Youth Day, but organizers scrapped the plan a few weeks ago.

In its place, victims' advocates have launched a campaign called “This is our memorial” and plan to put up billboards around Lisbon this week reading “4,800+ Children Abused.” St. John Paul II launched World Youth Day in the 1980s as a way to invigorate the next generation of Catholics in their faith, and the event is returning to European soil for the first time since 2016.

Ukrainian and Russian youths were expected to attend, and the war in Ukraine will likely take centre stage Saturday when Francis visits Fatima, the Catholic shrine which for over a century has been associated with an apocalyptic prophecy about peace and Russia.

“I think World Youth Day brings hope, after the pandemic, after being locked down, not able to live our faith as we were used to, as we wished for," Alfredo Hernandez, a World Youth Day volunteer from Guatemala, said. “The event gives a ray of hope to get out on the streets again.” Hot weather could be an issue during the five-day visit, given temperatures in Lisbon are expected to hit 35 C (95 F) on Sunday.

Many young people were expected to camp out in the vast, unshaded Tagus Park starting Saturday afternoon, first to participate in an evening vigil and then to be in place Sunday morning for Francis' final Mass.

Organisers said they installed 32 water tanks with 640 taps for filling water bottles, while the Lisbon City Council says it doubled the number of drinking fountains in the city to around 400.

Registered participants are receiving reusable water bottles and sunhats in their welcome knapsacks, but some were more worried for Francis, given his weakened condition: The 86-year-old Argentine pope was hospitalised for nine days in June to repair a hernia and remove scar tissue from previous intestinal surgeries.

Francis, who travels with a doctor and nurse on his foreign trips, is likely to refer to the heat given his repeated alarm about climate change, including as recently as last week, when he urged action in the face of wildfires ravaging Greece.

“I'm going to pray that he is going to be OK," Theresa Guettler, a nurse from Florida who is volunteering at the event, said. She recommended that Francis stay hydrated and follow his medical team's advice. “I trust that he has good doctors and good people taking care of him.”