Authorities in flood-hit Bangladesh and northeastern India scrambled on Monday to provide aid to more than nine million people marooned after the heaviest rains in years killed at least 54 people across both South Asian nations, officials said. Monsoon rains in low-lying Bangladesh have triggered catastrophic flooding in the northeastern Sylhet administrative division, leaving a quarter of its 15 million population stranded amid fast-rising waters and swollen rivers. “The flooding is the worst in 122 years in the Sylhet region,” said Atiqul Haque, Director General of Bangladesh’s Department of…