Officials in Indonesia and Sri Lanka battled on Wednesday to reach survivors of deadly flooding in remote, cut-off regions as the toll in the disaster that hit four countries topped 1,500. In Indonesia, survivors expressed growing frustration about the slow pace of rescue efforts and aid delivery, as humanitarian groups warned the scale of the challenge was almost unprecedented, even in a country that has faced no shortage of natural disasters. Monsoon rains paired with two tropical storm systems dumped record deluges across Sri Lanka, and parts of Indonesia’s Sumatra, southern Thailand and northern Malaysia last week. In Indonesia, 770 were confirmed dead, the country’s disaster management agency said on Wednesday, revising the toll down from 812 it announced earlier in the day. Another 463 people are also missing. Information is only trickling in as many regions remain physically cut off by flood damage, isolated by electricity and communications failures, or both. “It’s very challenging logistically to res...