The Major Floods in the Amazonas River and Tributaries (Western Amazon Basin) during the 1970–2012 Period: A Focus on the 2012 Flood*

Abstract

In this work, the authors analyze the origin of the extreme floods in the Peruvian Amazonas River during the 1970-2012 period, focusing on the recent April 2012 flooding (55 400 m 3 s 21 ). Several hydrological variables, such as rainfall, terrestrial water storage, and discharge, point out that the unprecedented 2012 flood is mainly related to an early and abundant wet season over the north of the basin. Thus, the peak of the Marañ on River, the northern contributor of the Amazonas, occurred sooner than usual (in April instead of May), coinciding with the peak of the Ucayali River, the southern contributor. This concomitance caused a dramatic flood downstream in the Peruvian Amazonas. These results are compared to the amplitude and timing of the three most severe extreme floods . The analysis of the climatic features related to the most important floods (1986, 1993, 1999, and 2012) suggests that they are characterized by a La Niña event, which originates a geopotential height wave train near the ground, with positive anomalies over the subtropical South and North Pacific and Atlantic and over southeastern South America. These patterns contribute to 1) the origin of an abundant humidity transport flux from the tropical North Atlantic and the Caribbean Sea toward the northwestern Amazon and 2) the maintenance of the monsoon flux over this region. They both favor a strong convergence of humidity in the northern Amazonas basin. Finally, the authors suggest that the intensity of floods is more likely related to an early La Niña event (as observed during the 2011/12 season), early rainfall, and simultaneous peaks of both tributaries of the Amazonas River.

Extreme Rainfall Events over the Amazon Basin Produce Significant Quantities of Rain Relative to the Rainfall Climatology

“…Manaus has been frequently faced problems due to large amounts of rainfall related to short period extreme events. Over the past 10 years the Amazon basin has experienced frequent flood and drought conditions [2]- [5] that directly impact the lives of its people. It is known that flood and drought conditions are strongly related to Pacific and Atlantic SST Sea Surface Temperature) anomalies, which affect the quantity of moisture that is available to converge/diverge over the Amazon region [6].…”

New Insights on Land Surface-Atmosphere Feedbacks over Tropical South America at Interannual Timescales

“…The pattern also exhibits the influence of the Pacific Decadal Oscillation (PDO) acting in phase-shift with Niño regions correlations (reverse sign of coefficients). This conjoint effect is triggered because the Amazon River basin occupies the largest portion of TropSA and several SST-modes determine the characteristics and magnitude of the interannual anomalies therein [57,[71][72][73]. …”

Sediment budget in the Ucayali River basin, an Andean tributary of the Amazon River

“…At the inter-annual time-scale, several studies describe that a significant fraction of rainfall variability in the southern AndesAmazon region is related to the El Niño Southern Oscillation (Garreaud et al, 2008). In general El Niño years tend to be dry, while La Niña years are often associated with wet conditions and floods (Espinoza et al, 2013;Lavado et al, 2013). One of the major extreme precipitation cells known in the Eastern cordillera is located above the Pachitea basin (Pa in Fig.…”