Scientists agree that climatic events such as storms and heavy rainfall could become more intense as the climate changes.

New research suggests that global warming not only increases the likelihood of such events, but also leads to greater extremes in rainfall, making moves to tackle global warming and implement measures such as improved flood defences increasingly important.

Global warming is now taking place, and recent flooding and heavy rainfall in parts of Europe highlight the increasing frequency of extreme weather events. Scientific understanding of how rain and other precipitation (such as snow or hail) forms is limited, as is the ability to model these processes in global and regional climate models.

Many assumptions about how extreme rainfall changes with temperature depend upon the Clausius-Clapeyron (C-C) relation. This predicts how much water vapour can be maximally contained in the air at any given temperature and pressure. The equation is used to help predict future changes in extreme precipitation, based on the following assumptions:

* Warmer air can hold more water vapour, with the potential to condense and form raindrops if the air cools.

* The total amount of rain in a downpour is mainly determined by the amount of water already in the atmosphere.

* Air generally circulates upward producing precipitation, but this does not vary much with climate change. Scientists consider the first two assumptions valid, but the third is less certain.

The study also provides a means of checking the accuracy of our climate change predictions, and suggests that climate models greatly underestimate the effect of temperature on rainfall intensity. New types of climate change models may therefore be needed in order to represent the greater intensity of extremes in precipitation as temperatures rise. 1. This research is part of the ENSEMBLES project, supported by the European Commission under the sixth framework programme.