Two studies published in Nature reveal that the rise in green house gas emissions has increased the amount of rainfall throughout the northern hemisphere, including the UK. In a letter to Nature, ‘Human contribution to more-intense precipitation extremes,’ researchers said ‘…human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas.’
From the study that focused on England and Wales in autumn 2010:
‘The precise magnitude of the anthropogenic contribution remains uncertain, but 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%.’ doi:10.1038/nature09762
This from New Scientist about how the modelling was done:
Modelling flooding is quite a bit harder than modelling a heatwave, however. Predictions can’t just take into account how much rain might fall: they also have to account for things like how waterlogged the soil was, and where the rainfall flowed.
To complicate matters further, the level of detail – in terms of both space and time – in global climate models is too coarse to allow the simulation of individual rainfall events. The models can make only broad statements about how rainfall is likely to change regionally over the course of decades or a century.
To overcome these problems, Allen and his team combined a seasonal weather-forecasting model with a rainfall run-off model, which predicts the flow of water over land.
Then they harnessed the number-crunching power of the thousands of personal computers that have signed up to Climateprediction.net. In this “citizen science” experiment, people offer up slack capacity on their computers to Allen’s team, who use it to run their climate models in the background. Nearly 55,000 people are currently signed up. ‘Blame human emissions for British floods.‘ New Scientist
What’s interesting is that this study was done by having volunteers run climate models on their local computers:
All simulations ran under Windows and Linux operating systems, in a global network of publicly-volunteered computers using climateprediction.net11, 12 client-server distributed computing architecture.
We fed each completed simulation’s England and Wales total daily precipitation time-series from April 2000 onwards into our precipitation-runoff model28, to synthesize September 2000 to November 2000 daily river runoff. doi:10.1038/nature09762
Also, as discussed in the debate on the effects of climate change, climate modelling itself has its own limitations, but could actually be underestimating the role of climate change in extreme weather events:
Changes in extreme precipitation projected by models, and thus the impacts of future changes in extreme precipitation, may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming16. doi:10.1038/nature09763
‘Blame human emissions for British floods.’ New Scientist
Pall, P., Aina, T., Stone, D., Stott, P., Nozawa, T., Hilberts, A., Lohmann, D., & Allen, M. (2011). Anthropogenic greenhouse gas contribution to flood risk in England and Wales in autumn 2000 Nature, 470 (7334), 382-385 DOI: 10.1038/nature09762