A severe drought has pushed river levels in Brazil’s Amazon region to record lows, leaving isolated communities dependent on emergency aid and thousands of boats stranded on parched riverbeds. The drought fits a pattern of more extreme weather in the world’s largest rain forest in recent years and is, scientists say, an expected result of global warming. Last year, the region was hit by widespread flooding and in 2005 it endured a devastating drought. The level of the dark Rio Negro, a tributary to the Amazonas river and itself the world’s largest black-water river, fell to 13.63 meters (45 feet) on Sunday, its lowest since records began in 1902, according to the Brazilian Geological Service. Only last year it hit a record high of 29.77 meters (98 feet).