pbr 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.br ppbr 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.br ppbr The level of the dark Rio Negro, a tributary to the Amazonas River and itself the world's largest black-water river, fell to 13.63m on Sunday - the lowest since records began in 1902.br ppbr Solimoes River, another tributary of the Amazonas, has also reached its lowest level since 1982.br ppbr Due to the prolonged dry season, scorched riverbanks have collapsed and many residents of riverside villages lost their homes.br ppbr The shallow waters have exposed sandbanks and rocks and have made part of the river unavigable. Life in the vast Amazon river network depends to a large extent on boat transport.