Climatic and synoptic characterization of heat waves in Brazil

Geirinhas JL, Trigo RM, Libonati R, Coelho CAS,Palmeira AC
International Journal of Meteorology, Volume 38, Issue 4,

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According to the latest global and regional circulation models, the probability of occurrence of large heat waves (HWs), such as the 2003 European or the 2010 Russian events will increase significantly in the following decades under most climate scenarios. Currently, there are numerous studies for the Northern Hemisphere characterizing HWs and evaluating their impacts in several areas such as public health, economy, and agriculture. However, over South America, and in particular for Brazil, similar analysis is lacking despite its large geographical extension and numerous population potentially affected. Here we perform an assessment of HW events and characteristics recorded in six large Brazilian cities during the last five decades. The performed analysis reveals the existence of positive and significant trends in HW frequency since the 1980s, particularly for the cities of São Paulo, Manaus, and Recife. Over the last decades, Brasília was the city that recorded the highest number of days per year under a HW regime, contrasting with Rio de Janeiro that recorded the lowest value. The assessment of the large-scale atmospheric circulation patterns associated with summer HWs, indicated for Porto Alegre, São Paulo, Rio de Janeiro, and Brasília the presence of well-marked concentric and positive 500hPa geopotential height anomalies followed by positive 850hPa temperature anomalies. These anomalies are likely associated with quasi-stationary anticyclonic systems promoted by anomalous westward displacements of the South Atlantic Subtropical High System which are related to a weakening of other transients (and non-transient) systems such the Intertropical Convergence Zone (ITCZ) and the South Atlantic Convergence Zone. For Manaus, the identified anomalies are linked to a northward displacement of the ITCZ. This configuration is compatible with an increase in solar radiative pattern and decreased soil moisture, enhancing surface temperature values, possibly associated with positive feedback mechanisms between soil and the atmosphere.