On the opposite relation between extreme precipitation over west Amazon and southeastern Brazil: observations and model simulations

Abstract

During the austral summer of 2014 and 2015, a severe drought occurred in southeastern Brazil at the same time when flooding conditions were registered in the state of Acre in the western Amazonia of Brazil. This study aimed the identification of the atmospheric and oceanic large‐scale characteristics and regional features associated with these conditions, and verification of the Center of Weather Forecasting and Climate Studies/National Institute of Space Research (CPTEC/INPE) atmospheric global circulation model ability in reproducing the observed features. The state of Acre was chosen as a pilot area of the PULSE‐Brazil project – a web platform tool that contains climate, ecological and health data for Brazil. The observational data and model results were analysed for the climatological period of 1981–2010. Correlation analyses between precipitation over west Amazon and atmospheric and oceanic variables indicated the main patterns in both data sets. Extreme wet and dry Januaries over west Amazon were selected to explore the regional and large‐scale associated features. The general results of climate analyses indicated an opposite relation of precipitation between western Amazon and southeastern Brazil, in January, besides the typical precipitation dipole between the south Atlantic convergence zone and southeastern South America. This configuration is related to anomalous humidity flux at low levels and associated anomalous sea level pressure over southeastern South America induced by subsidence. The role of convection anomalies over the Pacific Ocean on South America anomalies is discussed. The wet and dry cases in Acre region display opposite atmospheric anomalies over South America that are linked to wavetrains over the Pacific Ocean, likely related to the opposite conditions of Indonesia‐Pacific tropical convection. Similar patterns of the dry cases were observed during January of 2014 and 2015. The model reproduced some observed atmospheric patterns related to precipitation extremes and the results are discussed in terms of regional and large‐scale climate variability.

Correlations Between Extreme Atmospheric Hazards and Global Teleconnections: Implications for Multihazard Resilience

“…ENSO episodes have been related to droughts in Amazonia and northeastern Brazil and flooding in the southeast (Cavalcanti, ), but there is anecdotal evidence that droughts and flooding occur in both positive and negative ENSO events. Cavalcanti et al () suggest a correlation between ENSO and January NW Brazil rainfall of r =− 0.3 to −0.5 (95% level): wet (dry) conditions in NW Brazil are associated with cold (warm) conditions in the equatorial Pacific Ocean. This relationship is opposite over SE Brazil, but no correlation values are provided.…”

Climate variability over South America‐regional and large scale features simulated by the Brazilian Atmospheric Model (BAM‐v0)

“…In Cavalcanti et al . () regional features of precipitation extremes in Southwestern Amazon and Southeast Brazil simulated by the model were well represented. However, the relations of extremes in South America with convection in Indonesia region, identified in observational data were not reproduced.…”

“…The observed pattern shows opposite relations between Northeast (NE)/Southeast (SE) and South (S)/Northwest (NW) South America (Figure b). This pattern is similar to the pattern of observed correlation between Southeast precipitation and the other grid points in South America (Cavalcanti et al ., ). The model reproduces the precipitation dipole, but the opposition between SE/NE and NW is not simulated.…”

Multivariate intraseasonal rainfall index applied to South America

“…The spatial pattern of this first mode shows a large area over central–eastern South America, including northeast, central‐western and southeast Brazil, besides the eastern Amazon region, with a negative signal, and smaller areas over the northwestern Amazon, extreme southern Brazil, Uruguay, and nearby areas of Argentina and Paraguay, with a positive signal (Figure a). An almost similar pattern was obtained by Cavalcanti et al () in composites of extreme precipitation in the western Amazon in January, associated with humidity flux anomalies forced by atmospheric circulation anomalies likely related to the MJO. In that pattern there were opposite anomalies between the western Amazon and southeastern Brazil, besides the precipitation dipole associated with the SACZ.…”