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

Abstract:

Eastern South America can experience severe droughts that are accompanied by heatwaves as well as marine heatwaves in the western South Atlantic. Here, we show that while these multivariate events have the same driver and modulator, they have several impacts. Atmospheric blocking triggered by tropical convection in the Indian and Pacific oceans can cause persistent anticyclonic circulation that not only leads to severe drought and heatwaves but also generates marine heatwaves in the adjacent ocean. The anomalous anticyclonic circulation off southeast South America prevents synoptic systems reaching the region while inhibiting the development of the South Atlantic Convergence Zone and its associated rainfall. 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 atmospheric blocking and droughts, explains approximately 60% of the heatwaves over land and marine heatwaves in the western South Atlantic. Their impacts include water and power shortages in southeast Brazil, a region that is heavily populated, home to more than 80 million people, and responsible for 60% of the Brazilian gross domestic product. They can reduce Brazilian soy, coffee and sugarcane production, impacting food supplies globally and increasing worldwide prices. They decrease the production of oysters and the catch of some commercially important fish species, while decimating clams along the southern coast of Brazil. They can affect human health by driving dengue fever outbreaks in urban areas that can increase the number of fatalities. In addition, compound events like this have a disastrous impact on ecosystem degradation and loss of land and marine biodiversity.