Inundations in the Mamore basin (south-western Amazon-Bolivia) and sea-surface temperature in the Pacific and Atlantic Oceans

Extensive inundations have been observed in the Llanos de Mojos (Mamore basin, south western Amazon) causing social and economic disasters. Since the beginning of the seventies precipitations have increased in the Bolivian lowlands (Llanos) and in the over-rainy eastern Cordillera and Andean foothills (Yungas) and inundations have become more frequent. As a result inundations have been investigated in relation to rainfall over the Mamore basin in Trinidad-Puerto Varador and, in order to determine whether they are predictable, in relation to Sea Surface Temperature (SST) in the Atlantic and the Equatorial Pacific Oceans. The methods are correlation and composite techniques. As expected, during the 1945-1946/1998-1999 period, inundations have been associated with abundant rainfall in the Mamore basin, mainly in the Llanos and Yungas. The role of rainfall in the inner dry Andes and downstream from Trinidad is more limited. When consecutive floods are observed, the ground water storage contributes to the occurrence of the second or third inundation event and rainfall anomaly is generally weaker. Rainfall in the Mamore basin is hardly associated with Sea Surface Temperature Anomalies (SSTA) in the Pacific and Atlantic Oceans during the 1952-1953/1998-1999 period. However, during the nineties the southern Atlantic SSTA account for 50 percent of rainfall variability. Inundations are also related to negative SSTA differences between the tropical and subtropical southern Atlantic. Two thirds of the 22 inundation events occurred in association with this oceanic anomaly that features a weak SSTA gradient in the southern Atlantic. During the 1988-1989/1998-1999 period, a particularly significant relation can be observed between SSTA and inundations events. Despite being associated with major El Nino events (1982-1983, 1991-1992), inundations are not significantly related to the equatorial Pacific SSTA. (C) 2004 Elsevier B.V. All rights reserved