Outline Approach Data sets PAR fPAR C4/C3 LUE optimization

Approach GPP = LUE × APAR = LUE × fPAR × PAR PAR = SW × R PB C4 and C3 LUE and fPAR algorithm

Data set: Ameriflux Site Ameriflux GPP observations were used to minimize the discrepancy between modeled and observed GPP Sites with more than one year data during 2004 to 2006 were chosen Monthly GPP calculated from half-hourly GPP fluxes

Data set: fPAR products EVI/NDVI-derived fPAR – Monthly EVI/NDVI – Original: 0.05 deg – Used in model: 0.5 deg MODIS fPAR – Monthly MODIS fPAR – Original: 0.05 deg – Used in model: 0.5 deg SeaWifs fPAR – Monthly, Jan – June – Last 6 months were restructured by monthly mean from previous years – Original: 0.25 deg – Used in model: 0.5deg

Data set: radiation GEOS-5 surface net shortwave radiation and surface albedo – 3-hourly; 2004 – 2006; 2×2.5 deg SRB PAR and SW – Monthly; ; 1 deg CERES PAR and SW – Monthly; ; 1 deg BSRN measured SW – Monthly;

Data set: C4 distribution Global C4 percentage – 1 deg Africa C4 percentage – 1 km

EVI/NDVI-derived fPAR Area distribution of global EVI according to biome types Linear function applied to covert EVI/NDVI to fPAR Upper bound: top 25% EVI of topical rainforest Lower bound: EVI in Sahara desert with annual rainfall less than 25 mm

PAR Adjustment for GEOS-5 shortwave radiation – Downward SW = net SW / ( 1 - albedo ) – Ratio of SRB SW to GEOS SW Conversion from shortwave radiation to PAR – Ratio of SRB PAR to SRB SW – High temporal resolution PAR using GEOS-5 adjusted SW

APAR = PAR × fAPR

C4 photosynthesis Algorithm A – Same fPAR for C3 and C4 – Separate APAR according to C3 and C4 spatial distribution Algorithm B – Allocate most of the fPAR seasonal cycle to C4 – Separate APAR with different fPAR for C3 and C4

C4 LUE Lobell ratio: – Mean C4 LUE: 0.66 g C/MJ – Mean C3 LUE: 0.29 g C/MJ Ameriflux ratio: – Cropland rotation sites – Mean C4 GPP/mean C3 GPP = 1.32

LUE optimization A range of LUE was used to calculate GPP using the paradigm: GPP = LUE × APAR Just account for monthly GPP from all C3 sites and rotation site with C3 crops C4 LUE calculated from the Lobell and Ameriflux ratios