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Detection of a direct carbon dioxide effect in continental river runoff records
Primary Topic:Vulnerability & Adaptation
Document Author (other):C. Huntingford & P. A. Stott, N. Gedney, O. Boucher, P. M. Cox, R. A. Betts
Publication Date:2006 February 6
Continental runoff has increased through the twentieth century despite more intensive human water consumption3. Possible reasons for the increase include: climate change and variability, deforestation, solar dimming4, and direct atmospheric carbon dioxide(CO2)effects on plant transpiration. All of these mechanisms have the potential to affect precipitation and/or evaporation and thereby modify runoff. Here we use a mechanistic land-surface model and optimal ﬁngerprinting statistical techniques to attribute observational runoff changes into contributions due to these factors. The model successfully captures the climate-driven inter-annual runoff variability, but twentieth-century climate alone is insufﬁcient to explain the runoff trends. Instead we ﬁnd that the trends are consistent with a suppression of plant transpiration due to CO2-induced stomatal closure.This result will affect projections of fresh water availability, and also represents the detection of a direct CO2 effect on the functioning of the terrestrial biosphere.