Abstract
Abstract. We evaluate the ISBACC (Interaction Soil Biosphere Atmosphere Carbon Cycle) land surface model (LSM) over the Amazon forest, and propose a revised parameterization of photosynthesis, including new soil water stress and autotrophic respiration (RA) functions. The revised version allows the model to better capture the energy, water and carbon fluxes when compared to five Amazonian flux towers. The performance of ISBACC is slightly site dependent although similar to the widely evaluated LSM ORCHIDEE (Organizing Carbon and Hydrology In Dynamic Ecosystems – version 1187), which is based on different assumptions. Changes made to the autotrophic respiration functions, including a vertical profile of leaf respiration, lead to yearly simulated carbon use efficiency (CUE) and carbon stocks which is consistent with an ecophysiological meta-analysis conducted on three Amazonian sites. Despite these major improvements, ISBACC struggles to capture the apparent seasonality of the carbon fluxes derived from the flux tower estimations. However, there is still no consensus on the seasonality of carbon fluxes over the Amazon, stressing a need for more observations as well as a better understanding of the main drivers of autotrophic respiration.
Highlights
The Amazon rainforest plays a crucial role in the regional energy, water and carbon cycles, thereby modulating the global climate system
We evaluate and compare three versions of ISBACC: control version (CTL), photosynthesis components (PS) and parameterization of respiration (PS+R) described in Sect. 3.1, 3.2 and 3.3, respectively
We illustrate the uncertainties linked to the choice of model by showing the fluxes simulated by the wellevaluated ORCHIDEE (v.1187) land surface model (LSM) over the same sites
Summary
The Amazon rainforest plays a crucial role in the regional energy, water and carbon cycles, thereby modulating the global climate system. Despite intense deforestation and land use change, this region has acted as a long-term carbon sink (Phillips et al, 2008; Gatti et al, 2010, 2014; Gloor et al, 2012; Espírito-Santo et al, 2014), meaning that the carbon uptake by photosynthesis exceeded on average the carbon released by autotrophic respiration (RA) and decomposition. Recent observations showed that the Amazon sink has already been weakened by environmental perturbations such as deforestation (Lewis et al, 2009; Aragao et al, 2014; Pan et al, 2011) and extreme droughts (Marengo et al, 2011; Gatti et al, 2014). The response of the Amazon sink to the combined pressures of deforestation and climate change would be dramatic, especially as a majority of climate models project dryer and longer dry seasons at the end of the century (Fu et al, 2013; Joetzjer et al, 2013)
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