© Crown copyright Met Office ACRE working group 2: downscaling David Hein and Richard Jones Research funded by

© Crown copyright Met Office Overview Relevance Practical requirements Science questions What needs coordinating

© Crown copyright Met Office Relevance – what downscaling linked to ACRE has to offer Reconstruction of past weather events 20CR provides a reconstruction of the evolution of the past 130 years of weather at relatively coarse resolution (2x2 degrees) Downscaling this reconstruction can provide: High resolution reconstructions of specific weather events Good estimates of decadal variability of high resolution climate features Improving statistical downscaling Training statistical downscaling on 20CR data combined with long station records where available would provide more robust statistical transfer functions

© Crown copyright Met Office The importance of decadal variability Results from a 3-member ensemble projection for Europe using identical models and emissions to sample impact of natural variability Patterns of change locally are often different, especially in summer Differences are due solely to the influence of natural internal variability Run 1, winter Run 2, summer Run 3, winter Run 2, winter Run 1, summer Run 3, summer Change (%) Change in upper 5% of wet days by for SRES A2 scenario

© Crown copyright Met Office Practical requirements – I Access to 20CR 20CR comprises a 56-member ensemble reconstruction of the past ~130 years at 6-hourly intervals which poses significant data acquisition issues Storage of and making accessible the data requires significant technical and human resources – as does obtaining and manipulating the data Interfacing to dynamical downscaling Dynamical downscaling models require interfaces to be built in order to apply 20CR as driving data for the models

© Crown copyright Met Office Practical requirements – I I Ensemble member selection Downscaling the ensemble mean of 20CR does not make sense scientifically – high frequency transients, especially in relatively data-sparse areas, will be smoothed out thus high frequency variability in the downscaled reconstruction will be underestimates Downscaling the full 56 members will be impractical in many applications and thus a methodology and post-processing will be required to select a subset of the ensemble to downscale

© Crown copyright Met Office Science questions Estimating high resolution climate variability Downscaling the full 56 ensemble members could provide estimates of small-scale climate variability: e.g. how predictable is a particular extreme event given a certain large-scale forcing What is the value of 20CR + downscaling in estimating full spectrum multi-decadal variability? Can this be quantified (and errors estimates) via a validation of a downscaling of 20CR where data are available Can we deduce the drivers of damaging weather events through an analysis of diagnostics from 20CR downscaled reconstructions of them?

© Crown copyright Met Office So what activities related to downscaling need co-ordinating? Three areas would clearly benefit from coordination: Data dissemination and post-processing requirements Guidance on ensemble application and selection Information on scientific findings and research activities We would be interested to hear any other ideas or offers of assistance in any of these

© Crown copyright Met Office Some initial activities related to ACRE working group 2 Development of an interface to drive the Hadley Centre regional climate modelling system PRECIS with 20CR Application of PRECIS to study the rainfall associated with the 1894 Thames flood Downscaling of several ensemble members for analysis of issues surrounding predictability and ensemble selection Incorporation of the interface in the next version of PRECIS (V2) to be released to the PRECIS community in a few months