cc: "Birgitte von Christierson" date: Tue Jul 28 12:05:07 2009 from: Phil Jones subject: Re: Sampling UKCP09?! to: "Steven Wade" Steven, We'll discuss this with Geoff next week. A few things In your 3) the way MOHC produced the probabilistic projections GCMs and RCMs (with their perturbed physics) were given greater weight if they simulated the 20th century better. This is a part validation, so better models and parameter sets get preferred. In 4) not clear what 'more homogeneity than the 11 RCMs' means? Your key bullet lower down is the third one. You do need to sample the full range - somehow. This is difficult to do in the joint probability case. In 5) totally agree that you can get very different results depending on how you sample UKCP09. This should be clear from reading the reports, but it is difficult to get across when people use UKCP09 as a tool - without complete understanding. The one thing you don't mention relates back to the work we did for the EA project in 2005/6. This is that it is still very likely that historic droughts will be more extreme than future ones. This is because the GCMs and RCMs and the WG don't do low-frequency variability very well. The WG will have reasonable extremes, but is unlikely they will bunch together into drier and wetter decades and bi-decades. This is discussed in the large report under blocking, and also in the WG report. The WG may not do 2-3 year droughts that well - but neither will the RCMs. Cheers Phil At 10:19 27/07/2009, Steven Wade wrote: Phil, I wondered whether you might have a view on how to make UKCP09 a little more practical for water companies? I attach a note on our attempt to capture the range of UKCP09 by using Optimal Latin Hypercube Sampling that makes sure we can sets of factors that cover a reasonable range of UKCP09 and maintain characteristics of the Met Office emulator outputs (combined probabilities in P and T for each season and between seasons) We are suggesting that using 10-20 samples is a good first step and use of say 100 Weather Generator runs would come later for sites where there are significant risks. You must of tackled some of the same issues trying to make your WG outputs consistent with UKCP09 (?) so I would welcome your opinion on this. Regards, Steven Steven Wade - Group Manager Water Management HR Wallingford Ltd Howbery Park, Wallingford, Oxfordshire OX10 8BA, United Kingdom e: s.wade@hrwallingford.co.uk t: +44 (0) 1491 822214 (direct), +44 (0) 1491 835381 (switchboard) f: +44 (0) 1491 825916 (direct), +44 (0) 1491 832233 (general) [1]www.hrwallingford.co.uk ********************************************************************** HR Wallingford uses Faxes and Emails for confidential and legally privileged business communications. They do not of themselves create legal commitments. Disclosure to parties other than addressees requires our specific consent. We are not liable for unauthorised disclosures nor reliance upon them. If you have received this message in error please advise us immediately and destroy all copies of it. HR Wallingford Limited Howbery Park, Wallingford, Oxon, OX10 8BA, UK Registered in England No. 02562099 ********************************************************************** Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email p.jones@uea.ac.uk NR4 7TJ UK ----------------------------------------------------------------------------