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

© 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

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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

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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

-80 -40 -20 -10 -5 5 10 20 40 80Change (%)

Change in upper 5% of wet days by 2071-2100 for SRES A2 scenario

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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

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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

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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?

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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

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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