Amazon absorbed less carbon during the El Niño weather event

October 10, 2018

The Amazon rain forest absorbed less carbon during the 2015/2016 El Niño. This is apparent from a special issue of Philosophical Transactions of the Royal Society B that was published today. Ten Wageningen University & Research researchers contributed to the special issue and two of the articles were written by members of the Department of Meteorology and Air Quality. WUR also contributed to other articles.

El Niño, the strong warming of cold seawater that occurs once every three to seven years, influences the weather in large areas of the world. The 2015/2016 El Niño caused a severe drought in the tropics, the worst in decades. New research technology has enabled the researchers to conduct an in-depth examination of the influence of drought on carbon absorption in the Amazon rainforest and further unravel the nature of carbon cycles in the tropics. "We used satellite observations of fluorescence by chloroplasts to estimate the carbon uptake through photosynthesis," says Gerbrand Koren, PhD candidate with the Department of Meteorology and Air Quality, and the first author of one of the articles by WUR.

Sattelite observations and models

Tropical forests are susceptible to heat and drought, which can result in forest fires and reduced carbon absorption. El Niño had a major impact on the tropical forests in the Amazon in 2015/2016. The researchers endeavoured to understand and quantify this impact using methods that included satellite observations and models of the surface hydrology and the terrestrial biosphere. They examined the changes in the forests as compared to normal years. Precipitation during the El Niño was the lowest in 35 years, which resulted in a great reduction of both the amount of river water and the availability of soil moisture. Model studies revealed that the river discharge in the Amazon basin decreased by 30 to 40 percent from October 2015 onwards.

Less water available

The researchers found that less water was available for trees in the eastern part of the Amazon basin in particular. Gross primary production was greatly reduced throughout the Amazon region: tree photosynthesis was about 10 percent lower than in normal years. However, productivity rapidly returned to normal levels once the clouds returned and the rain season began, although the soil was still very dry. Ingrid van der Laan-Luijkx and authors including PhD candidate Erik van Schaik wrote the second WUR article. “We used a new combination of models together with observations,” Ingrid explains. “Using this combination resulted in new insights into the response of tropical vegetation to drought, insights that are necessary for a better understanding of the potential consequences of climate change.”