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Britain Faces More Flash Floods Due To Global Warming Claims Met Office

02.06.2014
02.06.2014 07:11 Age: 122 days

New research from the UK Meteorological Office predicts that Britain will experience an increase in the number of short, intense, rain storms that can result in flash flooding as a result of global warming increasing the capacity of the air to carry water vapour.

Click to expand. Difference between 2100 and present-day for the 1.5 km resolution models. Heavy rainfall is defined as the mean of the upper 5% of wet values (>0.1 mm/hr). White indicates differences or future changes not significant at the 1% level compared to year-to-year variability. Purple indicates the greatest differences. The radar data has been bias corrected using daily rain gauge data. Courtesy: Met Office and Nature Climate Change. Click to enlarge.

 

Short duration rain events are predicted to intensify during the summer months in the southern UK, reports a Letter published online in Nature Climate Change this week.

This predicted increase means more events would exceed the UK Met Office and UK Environment Agency Flood Forecasting Centre guidance threshold for serious flash flooding.

Changes in precipitation extremes are occurring under climate change, as the atmosphere warms and the capacity of air to hold water vapour grows. The Clausius Clapeyron (CC) relation describes the rate of change of saturated water vapour pressure with temperature as approximately by around 7% per oC. Such an increase drives increased levels of precipitation. This research was aimed at investigating how this increase in atmospheric water content and precipitation would manifest on sub-daily timescales – and particularly, short duration rain storms.

The paper cites evidence from observational studies that suggests the intensity of short duration rainfall events grows more rapidly with temperature. “This seems to be a property of convective precipitation and may be explained by latent heat released within storms invigorating vertical motion, leading to greater increases in rainfall intensity,” the authors state in their paper.

This study used a high-resolution model, typically used for weather forecasting, to simulate hourly rainfall in the UK in the year 2100. Met Office scientist Elizabeth Kendon and colleagues used a model typically employed for weather forecasting to investigate hourly rainfall changes in the southern UK. The model’s high resolution — 1.5 km grid spacing — allows projections of rainfall events and intensities on an hourly timescale. The results confirmed previous findings of winter rainfall intensification and found that short-duration rainfall intensified in summer, increasing the risk of flash flooding.

The model confirmed projections from a coarser resolution model and previous findings of winter rainfall intensification. However, the coarser model was unable to project changes in summer downpours due to warming, which the higher resolution model was able to predict using accurate representation of local storm dynamics.

Abstract

The intensification of precipitation extremes with climate change is of key importance to society as a result of the large impact through flooding. Observations show that heavy rainfall is increasing on daily timescales in many regions, but how changes will manifest themselves on sub-daily timescales remains highly uncertain. Here we perform the first climate change experiments with a very high resolution (1.5 km grid spacing) model more typically used for weather forecasting, in this instance for a region of the UK. The model simulates realistic hourly rainfall characteristics, including extremes unlike coarser resolution climate models giving us confidence in its ability to project future changes at this timescale. We find the 1.5 km model shows increases in hourly rainfall intensities in winter, consistent with projections from a coarser 12 km resolution model and previous studies at the daily timescale. However, the 1.5 km model also shows a future intensification of short-duration rain in summer, with significantly more events exceeding the high thresholds indicative of serious flash flooding. We conclude that accurate representation of the local storm dynamics is an essential requirement for predicting changes to convective extremes; when included we find for the model here that summer downpours intensify with warming.

Citation

Heavier summer downpours with climate change revealed by weather forecast resolution model by Elizabeth J. Kendon, Nigel M. Roberts, Hayley J. Fowler, Malcolm J. Roberts, Steven C. Chan & Catherine A. Senior published in Nature Climate Change (2014) doi:10.1038/nclimate2258

Read the abstract and get the paper here.

Source

Nature press release.


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