Downscaling

The process of reducing coarse spatial scale model output to smaller scales.

In detail

There are two types of downscaling that have been used in UKCP09 in order to produce finer resolution projections.

Dynamical downscaling
Regional climate models (RCMs) are a type of dynamical downscaling. Dynamical downscaling uses atmospheric interactions in the coarser resolution GCM to develop a finer resolution model. In UKCP09 the dynamically downscaled RCM HadRM3 has been used to produce 11 runs of regional climate projections at the medium emission scenario (A1B) on a daily time scale. These 11 runs were used to timescale and downscale the larger ensemble of GCM runs.

Stochastic and statistical downscaling
The Weather Generator product in UKCP09 is an example of stochastic and statistical downscaling. The Weather Generator is based around a stochastic model that simulates future rainfall sequences. Other weather variables are derived from the rainfall states. Statistical measures within the Weather Generator are then modified according to the UKCP09 probabilistic projections.

• An overview of how probabilistic projections are created and presented in UKCP09 is described in Box 3 of the UKCP09 Briefing report.

• More details are provided in Chapter 3 of the UKCP09 Climate change projections report, including an overview of the methodology in Chapter 3.2.12. The dynamical downscaling approach used is explained in more detail in Chapter 3.2.11.

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