Recent intensification of Amazonian flooding extremes is linked to the tropical Atlantic warming and tropical Pacific cooling

The Amazonian River basin hosts the one of the major global deep tropical convective systems, and thus drives the global Hadley and Walker circulations and the global hydrological cycle. Changes in the water cycle and deep convection activity in this region are, however, largely affected by remote oceans, especially the tropical Pacific, via the Walker circulation. Climate models forced by increasing anthropogenic greenhouse gases project an overall drying condition over the Amazonian basin, consistent with the projected weakening of the global Walker circulation (Held and Soden, 2006; Vecchi and Soden, 2007). However, a study published in Science Advances pointed out that the hydrological cycle of the Amazonian basin has intensified since the late 1990s with more frequent hydrological extremes, consistent with other recent studies (e.g., Floor et al., 2013). The study showed that the recent strengthening of the Walker circulation played a key role in driving the observed intensification of the severe flooding in the Amazonian basin. The study further suggested that the recent change in the Walker circulation was largely driven by the warm tropical Atlantic surface temperatures, linked to the positive Atlantic Multidecadal Oscillation, and the La Nina-like tropical Pacific sea surface temperature anomalies, linked to the global surface warming hiatus (e.g., McGregor et al., 2014; Chung. et al., 2019).

Figure 2 from Barichivich et al. (2019): Intensification of the equatorial Walker circulation and increased flooding in Amazonia. (B) Observed wet season SST trends from the ERSST (extended reconstructed SST) data set and schematic representation of the overturning Walker cells in blue. (C) Trends in wet season SLP and wind stress from ERA-Interim reanalysis. All linear trends are given as the cumulative change over 26 years (1990–2015), and stippling indicates significance at the 90% confidence level.

Barichivich, J., Gloor, E., Peylin, P., Brienen, R. J., Schöngart, J., Espinoza, J. C., & Pattnayak, K. C. (2018). Recent intensification of Amazon flooding extremes driven by strengthened Walker circulation. Science advances, 4(9), eaat8785. https://advances.sciencemag.org/content/4/9/eaat8785