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

Abstract

Aims The Amazon basin plays an important role in the global carbon budget. Interannual climate variability associated with El Nino 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 Nino and central-Pacific (CP) El Nino. The impacts of two types of El Nino 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 EPand CP-El Nino events using observational data, IPCC-AR4 model output. Potential impacts of the two different types of El Nino 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 Nino years. During CP-El Nino 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. EPand CP-El Nino events produce strikingly different precipitation anomaly pattern in the tropical and subtropical Andes during the austral fall season: wetter conditions prevail during EP-El Nino years and drier conditions during CP-El Nino years. Temperatures are above-average year round throughout tropical South America during EP-El Nino events, especially during austral summer. During CP-El Nino 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 Nino 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 Nino years. In the CP-El Nino 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 Nino 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 Nino years in the near future.