On the cover, the southern Bavarian village of Eschenlohe in August 2005, partially evacuated after the river Loisach flooded following heavy rain. A significant effect of anthropogenic activities has already been detected in observed trends in temperature and mean precipitation. But to date, no study has formally identified a human fingerprint on extreme precipitation, and it has proved difficult to assess the human impact on specific types of weather events. Two groups now present evidence that anthropogenic greenhouse gases have significantly increased the probability of heavy precipitation and local flood risk. Min et al. compare observations and simulations of rainfall between 1951 and 1999 in North America, Europe and northern Asia. They find a statistically significant effect of increased greenhouse gases on the incidence of extreme precipitation events over much of the Northern Hemisphere land area. Pall et al. use publicly contributed climate simulations to show that increased greenhouse-gas emissions substantially increased the risk of flood occurrence during the extensive flooding in England and Wales in autumn 2000. In News & Views, Richard Allan discusses the technical challenges associated with predicting regional changes in the water cycle.
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