Wind speed variability across the UK between 1957 and 2011
journal contributionposted on 05.03.2014 by Simon Watson, Petros Kritharas, G.J. Hodgson
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Using surface data from 57 UK meteorological stations, a national (BADC-57) and regional wind index for the UK has been calculated for the period 1983 to 2011. For a subset of seven stations, an additional national index (BADC-7) has been calculated for the period 1957 to 2011. The indices show an annual variability of 4% over their respective periods corresponding to a variation in typical wind turbine capacity factor of 7%. These indices are compared with indices calculated from other sources, namely: an index generated using a gridded dataset of observed values interpolated across the UK; an index calculated from an area bounding the UK using the ERA-40 reanalysis dataset; indices calculated from bilinear interpolation of the ERA-40 reanalysis dataset to the 57 and seven stations; and another independent UK wind index. The indices show variation in trends with all showing some level of decline with the exception of that generated using the ERA-40 reanalysis dataset averaged over the UK which shows a significant increase. The various indices show varying degrees of agreement with correlation coefficients, after trends are removed, ranging between 0.611-0.979. The effect of changes in site exposure, instrument bias and measuring height were considered for the BADC-7 and BADC-57 indices. The change in instrument measurement height appears to have a significant biasing effect and it is likely that this along with changes in exposure at urban sites have caused the decline in annual wind speeds observed for some of the indices. There does not appear to be evidence for significant changes in large area (mesoscale) surface roughness. The correlation between annual mean wind speeds at the seven surface station sites used to calculate the BADC-7 index is seen to be quite weak indicating very localised variations in inter-annual variability. When regional differences in the index are investigated, it is seen that wind speeds show a very slight decline across the UK in all regions except the south-east, which shows a slight increase. The greatest decrease is seen in the north-west. These changes are in the same direction as the tentative predictions given by climate models for future changes in wind speed across the UK, though the uncertainty is large given the large degree of inter-annual variation.
- Mechanical, Electrical and Manufacturing Engineering