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Change factor

A set of change values calculated for all Weather Generator variables for a specified future time period. The change factors are obtained by calculating the difference between the modelled baseline climate and the climate given in the UKCP09 probabilistic projections, for each 25 km grid square.

In detail

In order to generate future daily and hourly synthetic time series of weather variables, change factors are calculated and are used to perturb the statistics of the Weather Generator (WG). These change factors are calculated on a calendar month basis using the UKCP09 probabilistic projections, and are calculated for each WG variable. The change factors used include changes in the averages of the climate variables and some additional statistical properties for rainfall and temperature.

  • An overview of how the Weather Generator works is provided in Section 1.3 of the UKCP09 Weather Generator report.

  • Further discussion of how the change factors were validated is provided in Chapter 3 and of how change factors are generated and used is in Annex 4.

  • A simpler application of change factors is in the process of morphing baseline climate.

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