El Niño and global warming push Amazon Rainforest drought to the extreme

El Niño is a climatic phenomenon that results in an anomalous warming of the equatorial region of the Pacific Ocean. It occurs on a cyclical basis approximately every three to five years. Together with the 'Southern Oscillation', this is one of the main modes of climate variability. Although its consequences can be seen on an essentially global scale, its impact of tropical rainforests, specifically the Amazon, is of particular interest, as its ecosystem is considered one of the main carbon sinks on the planet.

In some cases, as in the events of 1982/83 and especially 1997/98, the magnitude of El Niño has been extraordinarily intense. In 2014, alarms were raised due to the possibility of an imminent and intense El Niño event, similar to that of 1997/98, although, in the end, the conditions for this to happen were not in place. However, in 2015, conditions were reactivated, leading to the extreme phenomenon of 2015/16, which had a greater effect than any of the previous occurrences.

The study published in Scientific Reports demonstrates how, in this last case, the phenomenon is associated with unprecedented warming of the Amazon Rainforest, which reached the highest recorded temperature in the last four decades and probably in the last century, as well as a greater extent of extreme drought. The study also showed changed in the spatial distribution of areas of drought with conditions of higher-than-normal humidity in the south-eastern region of the Amazon and extremely dry conditions in the north-east, something that had already occurred in 2009/10, albeit with less intensity.

According to the scientists, this fact, not observed in the 1982/83 or 1997/98 episodes, explains that a greater warming in the central equatorial Pacific--when the phenomenon is known as El Niño Modoki--produces a different and distinct distribution of humid areas of the Amazon Rainforest and areas of extreme drought.

Some studies associate the current climate change scenario with a higher frequency of this type of phenomena, although there is still no clear consensus among scientists. The biggest impact of these extreme drought conditions on tropical rainforests is due to a decrease in the assimilation of atmospheric CO2, as well as an increased likelihood of fires and the consequent loss of biomass.

Pacific temperature anomalies currently show neutral conditions, with a probability slightly higher than 50% of entering a La Niña phase, the cold spell of this natural global climate cycle, although the drought is expected to persist over the next few months.

The research has been carried out on the basis of climate data and temperature and precipitation records generated by the European Centre for Medium-Range Weather Forecasts, the Met Office Hadley Centre and the Climate Research Unit of the University of East Anglia, as well as satellite images. Some of this data is avalabe on the Thermal Amazoni@ server instaled at (ipl.uv.es/thamazon/web).

The study involved researchers Juan Carlos Jiménez Muñoz and José Antonio Sobrino, from the Global Change Unit of the Image Processing Laboratory at the University of Valencia's Science Park, as well as scientists from the University of Chile, the University of Leeds, the University of Maryland, the Geophysical Institute of Peru, the University of Oxford and the Netherlands Meteorological Institute (KNMI).

J. C. Jiménez-Muñoz, C. Mattar, J. Barichivich, A. Santamaría-Artigas, K. Takahashi, Y. Malhi, J. A. Sobrino, G. Van der Schrier
Record-breaking warming and extreme drought in the Amazon rainforest during the course of El Niño 2015-2016