Predicting the effects of elevated CO2 concentrations on catchment carbon and water fluxes

Abstract:

Anthropogenic activities are increasing atmospheric CO₂ concentrations. Among the many observed and expected impacts of this on our climate and biosphere, one is the so-called CO₂ fertilisation effect. In this effect the efficiency with which vegetation can acquire carbon relative to its water use increases proportionally with CO₂ concentration, and this biological response has implications for both carbon and water balances. Despite considerable research into the impacts of CO₂ fertilisation, there is still uncertainty on the catchment scale response of vegetation to elevated CO₂.

Here we present a simple, conceptually based, generic model for quantifying how CO₂ fertilisation affects the structure, water use and productivity of vegetation. Using this new Carbon Use Efficiency (CUE) model we can account for Free Air Carbon Enrichment (FACE) experimental results from a diverse range of sites. We use the CUE model to estimate the effect of the ~18% rise in CO₂ over the past three decades on the globe’s vegetation cover, and transpiration and carbon assimilation rates.