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What to be aware of

There are a few things to be aware of when using the 11-member RCM.

1. It is not available in a user-friendly manner

The 11-member RCM information was not originally intended to be made publicly available. However, users have asked for it so it has been made available via the  Climate Impacts project website. It is not considered part of UKCP09 and less support is available to support users. 

You will only be able to able to access the 11-member RCM information from the Climate Impacts  project and not from the UKCP09 User Interface. You will not be able to create graphical output for the 11-member RCM data. 

2. There are model biases from the historical simulations

The 11-member RCM simulations provide projections of absolute future climate rather than changes relative to the baseline. As with all data from climate models, data from the 11-member RCM contains biases, due to systematic errors of various sorts. 

The effect of historical model biases can be removed by differencing a baseline period from the future projections to get a climate change.

3. Enhanced resolution in the projections should not be taken to imply higher accuracy

As with any downscaling tool a Regional Climate Model (RCM) inherits all the uncertainties of the Global Climate Model (GCM) on which it is based. The detailed, fine-scale projections of the RCM should not be seen to provide greater accuracy. We recommend that you validate any climate variable of interest by comparing its baseline statistics with the relevant observed values wherever possible.

4. The 11-member RCM output cannot be used in conjunction with the UKCP09 probabilistic output

You should not use a variable from the 11-member RCM projections in conjunction with other variables from the UKCP09 probabilistic projections. This is because the two projections have been created in totally different ways. The 11-member RCM does not incorporate the large range of Hadley centre model projections nor the IPCC models which are incorporated in the UKCP09 projections. The two sets of projections are not comparable with one another.

5. They do not incorporate the full range of uncertainty available through the UKCP09 projections

Unlike the UKCP09 probabilistic projections, the 11-member RCM only represents projections from the Hadley Centre climate model (HadRM3) and does not take into account any other IPCC model projections. This is a significant limitation of the 11-member RCM.

There are also structural processes and uncertainties that are not taken into account in the HadRM3 model, which are taken into account in the UKCP09 probabilistic projections. The 11-member RCM does not include a full ocean or a carbon cycle.

In addition, only one emissions scenario is available for the 11-member RCM output. The use of only one emissions means that the 11-member RCM outputs may not be appropriate to use as part of a robust decision-making process.