MADRID -- Pope Benedict XVI urged more than 1.5 million young people to become missionaries for the faith Sunday, giving them words of encouragement as he concluded a glitch-marred church youth festival and announced that the next edition will be in Rio de Janeiro in 2013.

Benedict told the pilgrims at a Madrid airfield hosting World Youth Day that they should not keep their faith private but participate fully in the life of their parishes and remain in communion with the church.

"So do not keep Christ to yourselves! Share with others the joy of your faith," he said.

Hours earlier, a fierce thunderstorm during a prayer vigil at the airfield had forced Benedict to cut short his remarks and slightly injured six people when a tent collapsed. Some makeshift chapels set up on the field's perimeter were also damaged, forcing organizers to announce Sunday morning over loudspeakers that not everyone would be able to receive communion during the Mass.

In fact, Yago de la Cierva, head of the World Youth Day organizing committee, said almost none of the young people received the Eucharist during the Sunday Mass, a serious letdown for such fervent Catholics to be denied the sacrament.

Well worth the journey

Despite the discomfort and disappointment, pilgrims who spent the night in sleeping bags, tents and under tarps seemed unfazed as they awoke to sunny skies Sunday. Organizers announced they were opening a new area at the base to accommodate late arrivals.

"The night was amazing, I didn't sleep at all," said Adrinna Wista, a 21-year-old Polish pilgrim. "We stayed the night chatting, meeting new people and praying with them. Amazing."

Cristina Velasquez, a 29-year-old from Venezuela, said she spent the night with a group of Indian pilgrims after police, who had initially told her the airfield was full, let her in as the rain came down.

"Sleeping was difficult because the ground is quite stony. But waking up was indescribable, we are all so happy and united," she said. "The pope's words have made me proud to be making this sacrifice for his and Christ's sake."

Neither police nor the regional government have provided an official crowd count, but Vatican spokesman the Rev. Federico Lombardi said it was entirely "credible" that more than 1.5 million people took part.

This is Benedict's third World Youth Day, the gathering of young Catholics from around the world once every three years that was launched a quarter-century ago by Pope John Paul II in a bid to reinvigorate and spread the faith among the young. It has the feel of a weeklong rock concert and camping trip, with bands of flag-toting pilgrims roaming through Madrid's otherwise empty streets to take part in prayer and education sessions, Masses, cultural outings and papal events.

At the end of Sunday's Mass, Benedict officially announced that the next World Youth Day will take place in Rio in 2013 -- a year early to avoid conflicts with the 2014 World Cup in Brazil -- and said he hoped to attend. Brazilians in the crowd jumped, whooped and cheered at the announcement.

"I think this is great for Brazil and its youth because it's a very Catholic country," said Brazilian pilgrim Rogerio Moreira, 35. "It's a very good experience for those who can't attend other World Youth Days."

Before leaving for Rome, Benedict concluded his four-day visit with a farewell ceremony at Madrid's Barajas airport, where he praised this country that has seen Catholicism fall by the wayside in recent decades and where his visit was met by protesters opposed to the cost at a time of economic crisis.

"Spain is a great nation whose soundly open, pluralistic and respectful society is capable of moving forward without surrendering its profoundly religious and Catholic soul," he told the king and queen and other Spanish officials.