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Science  15 Nov 2013:
Vol. 342, Issue 6160, pp. 779
DOI: 10.1126/science.342.6160.779-c
CREDIT: © DBURKE/ALAMY

More intense precipitation events are expected to occur as climate warms. Warmer air holds more water vapor, relative humidity should not change as air temperatures increase, and precipitation intensity depends mostly on the availability of moisture in the atmosphere. Zhang et al. use updated observational data in a multimodel ensemble analysis of global climate model simulations available from the Coupled Model Intercomparison Project Phase 5 to quantify the human influence on extreme precipitation. They find that the model response to anthropogenic effects is consistent with the changes in extreme precipitation observed over land in the Northern Hemisphere and that the observed change cannot be explained by either natural internal variability or the response to natural external forcing. They estimate that the amount of rainfall over both 1- and 5-day intervals increased by between 5.2 and 5.9% between 1951 and 2005. This means that the single-day precipitation of a size expected to recur once every 20 years on average in the early 1950s has become an event that recurs every 15 years in the early 2000s and that the increased frequency is attributable to human influence.

Geophys. Res. Lett. 40, 5252 (2013).

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