The large impact of the 2015/2016 El Niño on the carbon and water balance of the Amazon derived from sun-induced fluorescence observations and modeling
Abstract
We studied the 2015/2016 El Nino event across the Amazon basin using two unique datasets specifically developed to understand ecosystem productivity and surface hydrology across this vast tropical forest area. We first created a new remotely-sensed sun-induced fluorescence product based on GOME-2A spectra, that is specifically tailored to retrieve reliable SIF signals in the wet and humid tropics. It reproduces observed seasonal cycles of GPP in tropical vegetation at Manaus very well, and captures regional spatial gradients in productivity without any prior knowledge on land-use, carbon fluxes, or NDVI. The second product is a high-resolution model ( 7km2) of surface hydrology that includes a detailed surface water transport and soil infiltration scheme. It reproduces observed river discharge at >100 stations across the Amazon basin very well in both magnitude, seasonality, and interannual variability. Simulated surface hydrology and observed productivity are linked quantitatively using the SIBCASA biosphere model.
We calculate 30-40% reduced river discharge in the Amazon starting in October 2015, lagging precipitation by 1 month, and in good agreement with river gauge observations. Soil moisture shows distinctly asymmetrical spatial anomalies with large reductions across the north-eastern part of the basin, which persisted into the following dry season. This added to drought stress in vegetation, already present due to high vapor pressure deficits at the leaf and subsequently high potential transpiration. As a consequence of this stress, we find that SIF went below its climatological range starting from the end of the 2015 dry season (October) and returned to normal levels by February 2016 (see Abstract Figure) when atmospheric conditions returned to normal, but well before the end of anomalously low precipitation which persisted through June 2016. Impacts were not uniform across the Amazon basin, with the eastern part experiencing much larger (10-15%) SIF reductions than the western part of the basin (2-5%). We estimate the integrated loss of GPP relative to eight previous years to be 0.34-0.48 PgC in the 3-month period Oct-Nov-Dec 2015. Integrating SIBCASA with the derived soil moisture stress, we confirm the high GPP anomaly and elucidate its regionally differing mechanisms.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMGC13B..01P
- Keywords:
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- 0322 Constituent sources and sinks;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0428 Carbon cycling;
- BIOGEOSCIENCESDE: 1615 Biogeochemical cycles;
- processes;
- and modeling;
- GLOBAL CHANGEDE: 4806 Carbon cycling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL