英文摘要: | During the winter of 2013/14, much of the UK experienced repeated intense rainfall events and flooding. This had a considerable impact on property and transport infrastructure. A key question is whether the burning of fossil fuels is changing the frequency of extremes, and if so to what extent. We assess the scale of the winter flooding before reviewing a broad range of Earth system drivers affecting UK rainfall. Some drivers can be potentially disregarded for these specific storms whereas others are likely to have increased their risk of occurrence. We discuss the requirements of hydrological models to transform rainfall into river flows and flooding. To determine any general changing flood risk, we argue that accurate modelling needs to capture evolving understanding of UK rainfall interactions with a broad set of factors. This includes changes to multiscale atmospheric, oceanic, solar and sea-ice features, and land-use and demographics. Ensembles of such model simulations may be needed to build probability distributions of extremes for both pre-industrial and contemporary concentration levels of atmospheric greenhouse gases.
Simulations by climate research centres1 project that raised levels of atmospheric greenhouse gas (GHG) concentrations are changing the climate system. This is detectable in temperature measurements with high statistical confidence2, and the algorithms leading to this statement pass robustness tests3. Simultaneously, there is evidence of a human-induced signal in some impacts, for example major sea-ice reductions4. For the UK, recent trends of increasing heavy rainfall events have been observed5. Increases in mean mid-latitudinal precipitation, when averaged to latitudinal bands, are sufficiently strong to allow attribution to raised GHG concentrations6. An anthropogenic influence has also been detected at high latitudes7, in seasonal precipitation8 and in thermodynamic and dynamic precipitation features9. Most general circulation models (GCMs) project increased global mean precipitation of order of 1–3% per degree of global warming10. Although some robust cross-GCM features exist11, there are important differences in the spatial patterns of change and even disagreement in sign in some regions, inhibiting attribution statements by comparison with observed precipitation. For the UK, however, over 90% of models in the Fourth Intergovernmental Panel on Climate Change (IPCC) assessment (Figs SPM7 and 10.9 in ref. 12) estimate mean precipitation increases for December–February for the period 2090–2099 under unmitigated emissions. The fifth IPCC assessment additionally reports for 2046–2065 (Fig. 12.22 in ref. 13), showing a multi-model mean precipitation increase. The latter is less than two standard deviations in variability, although at such earlier times signal strengths are smaller. Translating rainfall projections to flood risk, northwest Europe, including the UK, is therefore a region projected to experience increased flood frequency, with a relatively high consistency between GCMs (Fig. 1 in ref. 14).
| http://www.nature.com/nclimate/journal/v4/n9/full/nclimate2314.html
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