ITABUNA, Brazil—The death toll from floods hammering northeast Brazil rose to 20 on Monday, as the governor of Bahia state declared it the worst disaster in the state’s history, and rescuers braced for more rain in the coming days. Much of Bahia, home to about 15 million people, has suffered from intermittent flooding for weeks, after a long drought gave way to record rains. Flooding in some areas intensified late on Christmas Eve and early on Christmas Day after a pair of dams gave way, sending residents scrambling for higher ground. Rescue workers patrolled in small dinghies around the city of Itabuna, in southern Bahia, plucking residents from their homes, including some who escaped through second-floor windows. Bahia Governor Rui Costa said on Twitter that 72 municipalities were in a state of emergency. “Unfortunately, we’re living through the worst disaster that has ever occurred in the history of Bahia,” he …