Drought Legacy and the Impacts on the Amazon Forest Carbon Exchange

Abstract:

Sassan Saatchi^1,2, Yifan Yu¹, Xiang Xu², Luiz Aragao³, Liana Anderson³

¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

²Institute of Environment and Sustainability, University of California, Los Angeles, CA 90045. USA

³ Remote Sensing Division, National Institute for Space Research, São José dos Campos, Brazil, 12227-010, Brazil

Recent Amazonian droughts have drawn attention to the vulnerability of tropical forests to climate perturbations. Ground and satellite observations of 2005 and 2010 mega-droughts have shown an increase in fire occurrence and tree mortality during the period of drought. Here, we use a combination of satellite observations over a period of about 15 years to examine the legacy of the droughts in terms of impacts on the ecological structure and function of the forests in years following the droughts and the subsequent carbon exchange. Using data from microwave satellite sensors of rainfall, canopy backscatter (2000-2014) and GRACE and GOSAT, we show that the 2005 drought has a legacy of 2-5 years in western Amazonia, by increasing the disturbance in canopy trees and impacting the gross primary production of the forest significantly. Amazonian forests, particularly in the southern region were again impacted by the 2010 mega-drought, causing a legacy of 2-4 years with potential decrease in GPP and productivity observed by GOSAT fluorescence. The persistent of low canopy water content observed by a joint QSCAT and OceanSAT observations were linked to a delay in recharging of the hydrological system observed by GRACE over a period of 2-5 years. The results suggest that Amazonian forests with distinct dry seasons in southern and western regions of the basin are potentially more vulnerable to droughts compared to regions with less seasonality. The long recovery time from the 2005 and 2010 droughts suggests that the occurence of droughts in Amazonia at 5-10 year frequency may lead to long-term alteration of the forest structure and function.

Keywords: Amazonia, drought, carbon exchange, biomass loss, GPP