Researchers for the first time have identified human-induced global warming as a cause of the increasing frequency of flooding across the Northern Hemisphere and they warn that climate models apparently are underestimating the trend.
Theorists have pointed to a warmer atmosphere's ability to carry more water vapor and climate model simulations have pointed to the likelihood of more "extreme precipitation events," but two papers in the new issue of the journal Nature mark the first time that higher concentrations of greenhouse gases have been linked to actual events.
Animating a Changing ClimateThe team writes:
"Our results provide to our knowledge the first formal identification of a human contribution to the observed intensification of extreme precipitation. We used probability-based indices of precipitation extremes to facilitate the comparison of observations with models. Our results also show that the global climate models we used may have underestimated the observed trend, which implies that extreme precipitation events may strengthen more quickly in the future than projected and that they may have more severe impacts than estimated."
The second study by the Swiss researcher Pardeep Pall and colleagues focused on a particular event -- the UK floods of October-November 2000, the wettest autumn in England and Wales since records began in 1766. The team ran thousands of climate model simulations of the flooding that autumn and concluded that "in nine out of ten cases our model results indicate that twentieth-century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%."
In a separate evaluation of the two studies, UK research meteorologist Richard P. Allan of the University of Reading observes that while water vapor is a key ingredient, other potent factors are at work. "Subtle shifts in large-scale atmospheric circulation may affect local rainfall to a much greater extent than the thermodynamic processes relating to atmospheric water vapor content," he wrote.
IMAGE: A stone figure, that is equipped with scuba-gear, stands in a flooded garden in the village of Storkau, Germany, on 15 February 2011. Heavy rain and thaw have flooded parts of the village. Credit: Peter Endig/dpa/Corbis.
Tags: Climate Change, Floods, Global Warming, Meteorology
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