Impact of two different types of El Niño events on the Amazon climate and ecosystem productivity

Aims The Amazon basin plays an important role in the global carbon budget. Interannual climate variability associated with El Niño can affect the Amazon ecosystem carbon balance. In recent years, studies have suggested that there are two different types of El Ninos: eastern-Pacific (EP) El Niño and central-Pacific (CP) El Niño. The impacts of two types of El Niño on the Amazon climate and Amazon ecosystem are analyzed in the study. Methods A composite method has been applied to highlight the common features for the EP- and CP-El Niño events using observational data, IPCC-AR4 model output. Potential impacts of the two different types of El Niño on ecosystem carbon sequestration over the Amazon have been investigated using a process-based biogeochemical model, the Biome-BioGeochemical Cycles model (Biome-BGC). Important Findings Below-normal rainfall is observed year round in northern, central and eastern Amazonia during EP-El Niño years. During CP-El Niño years, negative rainfall anomalies are observed in most of the Amazon during the austral summer wet season, while there is average or above-average precipitation in other seasons. EP- and CP-El Niño events produce strikingly different precipitation anomaly pattern in the tropical and subtropical Andes during the austral fall season: wetter conditions prevail during EP-El Niño years and drier conditions during CP-El Niño years. Temperatures are above-average year round throughout tropical South America during EP-El Niño events, especially during austral summer. During CP-El Niño events, average or slightly above-average temperatures prevail in the tropics, but these temperatures are less extreme than EP year's temperature except in austral fall. These precipitation and temperature anomalies influence ecosystem productivity and carbon sequestration throughout the Amazon. Using the Biome-BGC model, we find that net ecosystem production (NEP) in the EP-El Niño years is below average, in agreement with most previous studies; such results indicate that the Amazon region acts as a net carbon source to the atmosphere during EP-El Niño years. In the CP-El Niño years, NEP does not differ significantly from its climatological value, suggesting that the Amazon forest remains a carbon sink for the atmosphere. Thus, even if CP-El Niño events increase in frequency or amplitude under global warming climate as predicted in some Global Climate Models, the Amazon rainforest may remain a carbon sink to the atmosphere during El Niño years in the near future.