EGU2020-5162
https://doi.org/10.5194/egusphere-egu2020-5162
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

From severe droughts in South America to marine heatwaves in the South Atlantic

Regina Rodrigues1, Andrea Taschetto2, Alex Sen Gupta2, and Gregory Foltz3
Regina Rodrigues et al.
  • 1Dept. Oceanography, Federal Universty of Santa Catarina, Florianopolis, Brazil (regina.rodrigues@ufsc.br)
  • 2Climate Change Research Centre and ARC Centre of Excellence on Climate Extremes, University of New South Wales, Sydney, Australia
  • 3NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, USA

In 2013/14 eastern South America experienced one of its worst droughts, leading to water shortages in São Paulo, the world’s fourth most populated city. This event was also responsible for a dengue fever outbreak that tripled the usual number of fatalities and reduced Brazilian coffee production leading to a global shortages and worldwide price increases. The drought was associated with an anomalous anticyclonic circulation off southeast South America that prevented synoptic systems reaching the region while inhibiting the development of the South Atlantic Convergence Zone and its associated rainfall. A concomitant and unprecedented marine heatwave also developed in the southwest Atlantic. Here we show from observations that such droughts and adjacent marine heatwaves have a common remote cause. Atmospheric blocking triggered by tropical convection in the Indian and Pacific oceans can cause persistent anticyclonic circulation that not only leads to severe drought but also generates marine heatwaves in the adjacent ocean. We show that increased shortwave radiation due to reduced cloud cover and reduced ocean heat loss from weaker winds are the main contributors to the establishment of marine heatwaves in the region. The proposed mechanism, which involves droughts, extreme air temperature over land and atmospheric blocking explains approximately 60% of the marine heatwave events in the western South Atlantic. We also identified an increase in frequency, duration, intensity and extension of marine heatwave events over the satellite period 1982–2016. Moreover, surface primary production was reduced during these events with implications for regional fisheries.

How to cite: Rodrigues, R., Taschetto, A., Sen Gupta, A., and Foltz, G.: From severe droughts in South America to marine heatwaves in the South Atlantic, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5162, https://doi.org/10.5194/egusphere-egu2020-5162, 2020

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Presentation version 1 – uploaded on 21 Apr 2020
  • CC1: Negative SST/SAT anomalies over Argentina, Syed Mubashshir Ali, 06 May 2020

    Hi Regina Rodrigues,

    Could you comment about whether the same mechanism lead to cold SST/SAT anomalies over Argentina possibly decreasing dry spells? In our climatological analysis for dry spells due to Recurrent Rossby Wave Packets (RRWPs), we find a similar pattern with an increase in dry spells over parts of Brazil due to an increase in RRWPs and a decrease over parts of Argentina. (https://meetingorganizer.copernicus.org/EGU2020/EGU2020-5168.html)

    Best Regards

    S. Mubashshir Ali

    • AC1: Reply to CC1, Regina Rodrigues, 07 May 2020

      Hi S. Mubashshir Ali,

      Probably yes, because when wave breaking occurs over eastern South America in austral summer, the moisture from the Amazon region is deviated to southern South America (enhanced South American Low-Level Jet), instead of feeding the SACZ in a normal summer situation. This leads to excess precipitation over Uruguay, Paraguay and parts of Argentina and characterizes the precipitation dipole over South America. More clouds also mean less shortwave radiation in the summer and cooler air temperatures. However, off Argentinian coast, SST are largely determined by changes in the Brazil-Malvinas Confluence, i.e., by ocean dynamics. You can find more details with respect to the droughts in Rodrigues & Woollings (2017, J. Climate) and with respect to the marine heatwaves in Rodrigues et al. (2019, Nature Geosc.).

      Thanks for your comment!

      Regina R. Rodrigues

      • CC2: Reply to AC1, Syed Mubashshir Ali, 07 May 2020

        Thank you for the insight and for the references.