Large scale and synoptic features associated with extreme precipitation over South America: A review and case studies for the first decade of the 21st century

Abstract

Flooding or droughts over South America affect the population and several sectors of the economy such as agriculture, energy and transport. Floods occur due to extreme precipitation from mesoscale precipitating systems, which can often be embedded in synoptic systems that are influenced by large scale conditions that are in turn influenced by climate variability. Droughts are associated with lack of or reduced influence of these synoptic systems, and also affected by persistent large scale conditions. El Niño–Southern Oscillation episodes have been related to droughts in Amazonia and northeastern Brazil and flooding in southeastern South America. Other extreme cases have been associated with Atlantic sea surface temperature (SST) anomalies. Extreme cases also occur in association with tropical–extratropical interactions, through atmospheric circulation anomalies in both tropics and extratropics. In the present review, studies of precipitation extremes in South America and some examples of extreme precipitation in several regions of South America in the 21st century are shown, and a discussion of the associated mechanisms is included. The influences of tropical and extratropical large scale climate variability — such as the Pacific and Atlantic SST, the Pacific South America pattern, the Southern Hemisphere annular mode and features of the North Atlantic Oscillation — on extremes over South America are mentioned. Daily precipitation extremes over South America are often related to convective development within synoptic systems, such as frontal systems and the South Atlantic Convergence Zone, in the Southeastern Brazil. Intertropical Convergence Zone and easterly disturbances are the main systems in which convective development can occur related to precipitation extremes in Northeastern region. In La Plata basin, extremes are associated with highly organized convective systems originating in the lee of the Andes that propagate eastward.