Detection of a direct carbon dioxide effect in continental river runoff records

A river runs off it Despite increasing human consumption of water, there was a general upward trend in continental-scale river runoff during the past century. Some researchers claim that this is due to climate change. Gedney et al. have investigated this using a mechanistic land-surface model and a statistical ‘fingerprinting’ method that allows contributions from individual factors to be identified. A climate-change driven component in runoff variation is evident, but is insufficient to account for the whole trend. A more influential factor is reduced plant transpiration due to CO2-induced stomatal closure. To date, this effect has been neglected in projections of future water resources. As CO2 concentrations rise in future, reduced plant water usage is likely to increase both the availability of freshwater and the risk of flooding, and to add to surface warming via reduced energy loss from evaporation.