Future UK circulation and wind projections and their relevance for the built environment.

Met Office Report, August 2010.

This EPSRC funded project highlights the uncertainty in future UK winds through analysis of multi model projections. A weather classification methodology has been used to explore how the frequency and characteristics of particular weather types are projected to change into the future. A comparison with ERA40 has highlighted that current Global Circulation Models (GCMs) have too many cyclonically classified days and too few anticyclonic days. In particular the models have too few UK centred intense high pressure days and too few runs of anticyclonic conditions. There are also too many UK centred weak cyclonic days and too many runs of cyclonic days in the models. The present day relationship between different weather types and average wind speeds across the UK has been determined and the specific weather types associated with high and low wind UK wide wind conditions highlighted. A future shift to more anticyclonic and less cyclonic days is seen across both ensemble datasets annually and particularly in summer and autumn. Detailed analysis has highlighted this future shift is from UK centred weak cyclonic days to low wind anticyclonic days, with an increase in consecutive days of anticyclonic conditions. The limited capability of different models to capture the characteristics of blocking anticyclones is well documented and should therefore be taken into account when interpreting the results. An increase in UK wide low wind anticyclonic conditions into the future could have important implications for society. During hot spells in the summer, higher wind speeds help building ventilation; these preliminary results indicate that overheating of buildings could increase into the future. UK wide anticyclonic events have also been seen to reduce wind power production across the UK and consequently the projected future increase in low wind events in summer and autumn, combined with an increasing reliance on wind power could compromise our future energy resilience. This work has demonstrated how weather type analysis can be used to help understand the societal impacts of climate change. Further work is required to fully assess the impacts of future circulation changes on specific societal sectors.

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