Blues fans were shocked by the Chinese-owned club's decision to replace the immensely popular Rowett with the club eighth in the Championship table.
"The difficulty was that my predecessor was doing very well," Zola told BBC WM.
"Sometimes that makes it not easy for a new manager, but I'm professional, it was a good opportunity and I could not refuse it," added the Italian, 50.
Zola played against Birmingham twice during his illustrious career with Chelsea.
He scored in both matches in the 2002-03 season - a 3-0 win at Stamford Bridge and a 3-1 win at St Andrew's - as part of a Chelsea team that also contained future Birmingham players Mario Melchiot and Jesper Gronkjaer.
A return to the Premier League is the main target for the former West Ham and Watford boss.
"When I was first asked two days ago, I said it is fine for me," he said. "It is a good club with good players and I like these things. It is a chance to build something and get in the Premier League as quickly as possible.
"The fact that the previous manager had done very well will make it more of a challenge but it will also make me more focused to become more accepted."
Brighton manager Chris Hughton, who takes his second-placed Seagulls side to Birmingham on Saturday, led Blues to the Championship play-offs in his one season in charge in 2011-12.
"My reaction was like most people, who were quite shocked," Hughton told BBC Sussex. "Gary's done a wonderful job in the period of time that he's been there and made real progress.
"In this day and age in football, there aren't many surprises, but that was one of them.
"It's wonderful to see Gianfranco back in the English game. Nobody will begrudge somebody of his stamp coming back in, but it will more a case of feeling for Gary. It's always sad to see a very good manager lose his job.
"We can only prepare ourselves like for any other game. They have some very good players and are now on the back of a good win against Ipswich."
Former Blues defender Michael Johnson knows Zola well, having done his FA coaching badge on the same course.
"He's one of the most decorated footballers in English football, somebody I now consider a friend," Johnson told BBC WM.
"He's a great guy, very well mannered and very well spoken but, make no bones about it, if he does not get his way and the players do not adhere to what he wants, he'll come down heavily on them.
"It will be difficult to get people onside in the outset. But, in Gianfranco Zola, they've got someone who can do well for them."
New Birmingham City boss Gianfranco Zola says he had to be "professional" about replacing Gary Rowett as manager.