We present a novel approach to estimating the transpiration flux and gross primary productivity (GPP) from Normalized Difference Vegetation Index, leaf functional types, and readily available climate data. We use this approach to explore the impact of variations in the concentration of carbon dioxide in the atmosphere ([CO2]) and consequent predicted changes in vegetation cover, on the transpiration flux and GPP. There was a near 1 : 1 relationship between GPP estimated with this transpiration flux approach and that estimated using a radiation-use efficiency (RUE) approach. Model estimates are presented for the Australian continent under three vegetation–[CO2] scenarios: the present vegetation and hypothetical ‘natural’ vegetation cover with atmospheric CO2 concentration ([CO2]) of 350 μmol mol−1 (pveg350 and nveg350), and for the ‘natural’ vegetation with [CO2] 280 μmol mol−1 (nveg280). Estimated continental GPP is 6.5, 6.3 and 4.3 Gt C yr−1 for pveg350, nveg350 and nveg280, respectively. The corresponding transpiration fluxes are 232, 224 and 190 mm H2O yr−1. The contribution of the raingreen and evergreen components of the canopy to these fluxes are also estimated.
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