Proxy and historical evidence for rainfall extremes in the Amazon and northeastern Brazil, 1790-1900
Historical accounts in the Brazilian Digital Library provide independent support for most of the tree-ring reconstructed wet season rainfall extremes in the eastern Amazon during the late-18th and 19th centuries. Newspapers, government reports, and other documents describe crop failure, livestock mortality, water shortages, and ship groundings on the Amazon River during many of the tree-ring reconstructed drought extremes. Heavy rains and flooding are described during some of the wet extremes, including the overtopping of the Bittencourt Bridge in Manaus by floodwaters during the tree-ring reconstructed wet year of 1892. The elevation of the Bittencourt Bridge in 1892 may provide a benchmark for comparison with modern flood extremes on the Rio Negro/Rio Amazon system. The “Unknown Drought” of 1865 was the lowest wet season rainfall total reconstructed with tree-rings in the eastern Amazon from 1759-2016 and appears to have been one of the lowest stream levels observed on the Amazon River during the historical era, according to descriptions by the Louis Agassiz-Major Coutinho Expedition and others. The economic impact of the drought in 1865 appears to have been moderated by the highly inflated price of cotton, which benefitted Brazilian growers, following the collapse of production in the American South during the Civil War. This may help explain why the extreme low water levels on the Amazon during the Unknown Drought have received limited scientific attention. The proxy and historical evidence for late-18th and 19th century rainfall extremes provide useful perspective on modern climate variability and change in the Amazon.