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The term used in UKCP09 to describe the way in which change factors at a monthly timescale are used to modify the underlying climatology at a daily time-scale in a way that is consistent with the UKCP09 probabilistic climate projections.

In detail

Climate events and conditions which occur on daily timescales are not well represented in the monthly-averaged output from global and regional climate models. Projections of climate on a daily timescale can be provided by using the UKCP09 Weather Generator which adjusts the baseline climatology to take account of projected monthly changes. For example, a particular scenario may indicate an increase in mean temperature of 2.4°C in January. This value would be added to the monthly mean temperature value for January in the baseline climatology as a change factor. The full procedure for applying these change factors is termed perturbing.

  • An overview of how the Weather Generator works is provided in of the UKCP09 Weather Generator report.

  • Further discussion of the perturbation methodology is provided in and validation of perturbation in .