Higher river levels as more carbon dioxide makes plants less thirsty

Posted: Tuesday 18th September 2007

Rising carbon dioxide (CO2) levels will increase river levels in the future, according to a team of scientists from the Met Office Hadley Centre, the University of Exeter and the Centre for Ecology & Hydrology.

The findings, published recently in the journal Nature, suggest that increasing CO2 will cause plants to extract less water from the soil, leaving more water to drain into rivers which will add to the river flow increases already expected due to climate change.

Last year, members of the research team showed that this effect can already be seen in historical river flow records. This new study, led by Dr Richard Betts, Climate Impacts scientist at the Met Office Hadley Centre, shows that the effect of plant responses to CO2 could be as important as those of increased rainfall due to man-made climate change.

The predictions are likely to be both good news and bad news. "It's a double-edged sword," said Dr Betts. "It means that increases in drought due to climate change could be less severe as plants lose less water. On the other hand, if the land is saturated more often, you might expect that intense rainfall events are more likely to cause flooding."

Dr Betts, a lead author on the recent IPCC report, added that this effect also makes it more difficult to compare CO2 with other greenhouse gases which do not affect plants in the same way. "We often hear about the CO2 equivalent of other gases such as methane and nitrous oxide, used in calculating carbon footprints. But this only accounts for the effect of these gases on global warming. If we want to compare their full impacts on droughts and flooding, we need to consider direct effects on plants too."

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