WHAT HAPPENED IN 2021? ANALYZING THE BIGGEST NEGRO RIVER FLOOD IN MANAUS, BRAZIL

Abstract

Flood and ebb processes are common events in any hydrological system. In some cases, due to natural or anthropogenic conditions, such events can take place in an extreme manner, causing a lot of damage to the population. In 2021, in several municipalities in the Amazon basin, rivers reached levels higher than the maximum observed until then, making this year the biggest flood in the entire history of monitoring. Most Amazonian rivers have a high annual pulse of floods, as a result of the precipitation period in the upper part of their large basins. Most of the floodplains located in the central region of Amazonia become inundated from May to July, from which the water drains into the river systems slowly over the drought time. In the Amazon Basin, extreme events are mainly related to El Niño or La Niña events, resulting in some big floods and a long rainfall period. In 2021, the Negro river level exceeded the maximum level observed in the entire 119-year historical series of monitoring. On 30 May 2021, the previous record of 29.97 m observed in 2012 was equaled. The river continued to rise until reaching the level of 30.02 m on 16 June 2021. Other stations monitored by Geological Survey of Brazil, which were accomplished through bulletins, reached historical records in the same year, such as São Gabriel da Cachoeira, Barcelos and Manaus (Negro river), Manacapuru (Solimões river), Careiro da Várzea (Amazon river basin), Itacoatiara and Parintins (Amazon river), all located in the state of Amazonas. This study analyzes the conditions that favored the event of the greatest flood recorded in the Rio Negro in 2021. Some factors contribute to the flooding event, such as the rainfall regime distributed throughout the basin and how the main river and its various tributaries behave during the flooding period.