Yi, Y., J. S. Kimball, L. A. Jones, R. H. Reichle, R. R. Nemani:
"Application of a satellite-based terrestrial carbon flux model for quantifying recent climate and fire disturbance impacts on northern ecosystem productivity"
Presentation at the AGU Fall Meeting, San Francisco, CA, USA, 2012.

Abstract:
Quantifying variability and underlying environmental constraints on carbon (CO2) sequestration in northern (>45 degrees N) ecosystems is important for improving predictions of future climate change. We applied a satellite-based terrestrial carbon flux model for daily estimation of net ecosystem CO2 exchange (NEE) and component carbon fluxes across a pan-boreal/Arctic domain. The model includes a light use efficiency algorithm for estimating vegetation gross primary production (GPP) using operational satellite NDVI records, while ecosystem respiration is derived using a three-pool soil decomposition model adapted to utilize potential inputs from satellite microwave retrieved soil moisture and temperature as primary environmental constraints to soil respiration. Initial validation against tower eddy-covariance measurement based carbon fluxes for northern tower sites showed favorable results for GPP (R>0.7, RMSE<2.5 g C/m2/day), and overall consistency for NEE (R>0.5) at predominantly undisturbed sites. However, the terrestrial carbon uptake during the peak growing season was generally underestimated by the model especially for deciduous broadleaf forests, mainly due to under prediction of GPP over dense canopy areas and model steady-state assumptions of dynamic equilibrium between vegetation productivity and respiration processes. A model framework integrating satellite-based burned area products and vegetation indices was then developed to represent non-steady-state fire disturbance and recovery effects and the simulations largely tracked NEE recovery indicated by tower CO2 flux measurements over three boreal fire chronosequence networks. The regional simulations indicated that large drought and fire events were generally associated with large GPP reductions and net ecosystem carbon losses, though NEE was generally less sensitive to fire disturbance due to similar behavior in GPP and respiration components. These results are being used to inform development of an operational carbon product for the NASA Soil Moisture Active Passive (SMAP) mission.


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