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Extreme weather events

Extreme weather describes weather phenomena that are at the extremes of the historical distribution, especially severe or unseasonal weather.

In detail

The meteorological or statistical definition of extreme weather events is events at the extremes (or edges) of the complete range of weather experienced in the past. Defined in this way, extreme weather events include, but are not limited to, severe events like heatwaves or intense rainfall. For example, the warmest day of winter could be described as a weather extreme.

UKCP09 provides probabilistic projections of changes in climate extremes that are based on the 99th percentile, or the value that is exceeded on only 1 in 100 days. Assuming each season is one hundred days long, this roughly corresponds to 1 day per season. This allows changes in variables such as warmest day in summer and wettest day in winter to be explored.

UK-wide maps showing these changes are shown in the Maps & key findings section.

Find out more


  • UKCP09 provides projections of changes in extreme water levels, or storm surge height, as represented by height. They are summarised in  of the UKCP09 Briefing Report with more details in  of the UKCP09 Marine & Coastal Projections report.
  • The UKCP09 Weather Generator permits extremes associated with daily climate to be investigated.  in UKCP09 Weather Generator report provides a list of some of the extremes that can be derived from Weather Generator output.  discusses issues associated with the use of Weather Generator outputs to investigate extremes.