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Understanding Interactions between Terrestrial Water and Carbon Cycles Using Integrated SMAP Soil Moisture and OCO-2 SIF Observations and Land Surface Models
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  • Zhijiong Cao,
  • Yongkang Xue,
  • Hara Prasad Nayak,
  • Dennis P. Lettenmaier,
  • Christian Frankenberg,
  • Philipp Köhler,
  • Ziwei Li
Zhijiong Cao
University of California, Los Angeles
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Yongkang Xue
University of California Los Angeles

Corresponding Author:[email protected]

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Hara Prasad Nayak
University of California Los Angeles
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Dennis P. Lettenmaier
University of California, Los Angeles, California, USA
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Christian Frankenberg
California Institute of Technology
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Philipp Köhler
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Ziwei Li
University of California Los Angeles
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Recently, more advanced synchronous global-scale satellite observations, the Soil Moisture Active Passive enhanced Level 3 (SMAP L3) soil moisture product and the Orbiting Carbon Observatory 2 (OCO-2) solar-induced chlorophyll fluorescence (SIF) product, provide an opportunity to improve the simulations of both water and carbon cycles in land surface modeling. This study introduces a mechanistic representation of SIF to the Simplified Simple Biosphere Model version 4 (SSiB4) coupled with the Top-down Representation of Interactive Foliage and Flora Including Dynamics Model (TRIFFID). This newly developed model with the observed satellite data indicates that introducing dynamic processes can lead to substantial improvement in global carbon flux simulation. In the SSiB4/TRIFFID/SIF, four critical soil and vegetation parameters–B parameter, soil hydraulic conductivity at saturation (Ks), wilting point, and maximum Rubisco carboxylation rate (Vmax)–were identified through numerical sensitivity experiments. Among the four parameters, the B parameter has the most significant effects on both soil moisture and SIF simulations. With the optimized B parameter, both soil moisture and SIF simulations were improved substantially, with especially significant improvement for shrubs. The Ks and wilting point also affect both soil moisture and SIF but with reduced magnitude. The Vmax directly affects photosynthesis, and its modification can substantially improve the SIF simulation of needleleaf trees and C3 grasses. With all four calibrated parameters based on SMAP L3 and OCO-2 data, the root-mean-squared error (RMSE) of soil moisture and SIF simulations decreased from 0.076 to 0.063 m3/m3 and from 0.143 to 0.117 W/m2/μm/sr, respectively.
23 Oct 2023Submitted to ESS Open Archive
08 Nov 2023Published in ESS Open Archive