Extreme seasonal droughts and floods in Amazonia: causes, trends and impacts

Abstract

This paper reviews recent progress in the study and understanding of extreme seasonal events in the Amazon region, focusing on drought and floods. The review includes a history of droughts and floods in the past, in the present and some discussions on future extremes in the context of climate change and its impacts on the Amazon region. Several extreme hydrological events, some of them characterized as 'once in a century', have been reported in the Amazon region during the last decade. While abundant rainfall in various sectors of the basin has determined extreme floods along the river's main stem in 1953, 1989, 1999, 2009, 2012-2015, deficient rainfall in 1912, 1926, 1963, 1980, 1983, 1995, 1997, 1998, 2005 and 2010 has caused anomalously low river levels, and an increase in the risk and number of fires in the region, with consequences for humans. This is consistent with changes in the variability of the hydrometeorology of the basin and suggests that extreme hydrological events have been more frequent in the last two decades. Some of these intense/reduced rainfalls and subsequent floods/droughts were associated (but not exclusively) with La Niña/El Niño events. In addition, moisture transport anomalies from the tropical Atlantic into Amazonia, and from northern to southern Amazonia alter the water cycle in the region year-to-year. We also assess the impacts of such extremes on natural and human systems in the region, considering ecological, economic and societal impacts in urban and rural areas, particularly during the recent decades. In the context of the future climate change, studies show a large range of uncertainty, but suggest that drought might intensify through the 21st century.

Hydroclimatic variables associated with El Nino and La Nina events at the Curuá-Una hydroelectric reservoir, Central Amazonia

“…Other studies on climate and hydrometeorological trends in the Amazon do not demonstrate unidirectional trends in large-scale precipitation or river flows (Marengo and Tomasella 2012;Marengo and Espinoza 2015). According to Dantas et al (2015) positive trends, but no statistical significance of meteorological variables are related to the absence of long-term data series.…”

“…The years of lower rainfall also exhibited effects on the flow of Curuá-Una reservoir. In particular, 1998 was an extremely dry year for much of the Amazon basin, with serious consequences in the transport, health, agriculture and energy and water supply sectors Tomasella et al 2010;Marengo and Espinoza 2015).…”

“…Seasonal variations in the location of the IntraTropical Convergence Zone (ITCZ) lead to a strong seasonal cycle in precipitation, with a wet season and heavy rains during JFM and a dry season during JAS (Fisch et al 1998;Wang and Fu 2007). The seasonal patterns in rainfall precede strong seasonal variations in the flow of rivers, which serve as integrators of hydrological processes within their watershed (Richey et al 2002;Ronchail et al 2005a;Marengo and Espinoza 2015). The seasonal cycle in river levels is of fundamental importance in wetland ecological processes (Junk et al 1989), transport of people and goods, and for decision making regarding creation and operation of hydroelectric dams (Fearnside 2008;.…”

A systematic assessment of drought termination in the United Kingdom

“…At national or continental scales, larger-scale drivers such as El Niño and La Niña events in the Pacific (e.g. Tomasella et al, 2011;Marengo and Espinoza, 2016), switches in Atlantic temperatures (Wilby, 2001;Folland et al, 2015), and tropical cyclones (e.g. Kam et al, 2013;Patterson et al, 2013) have been shown to be a factor in drought termination events.…”

Brazil’s Amazonian forest carbon: the key to Southern Amazonia’s significance for global climate

“…All of these are important areas for research in modeling carbon release from soils (Lehmann and Kleber 2015). Climate change is expected to affect both temperature and humidity, with longer and more severe droughts together with higher temperatures in Amazonia, especially southern Amazonia (Fu et al 2013;Marengo and Espinoza 2016). Slow-turnover soil organic matter is more sensitive to release under warming than is fast turnover organic matter (Conant et al 2008;Craine et al 2010;Davidson and Janssens 2006).…”