Journal cover Journal topic
Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 10, 2171-2199, 2014
http://www.clim-past.net/10/2171/2014/
doi:10.5194/cp-10-2171-2014
© Author(s) 2014. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
12 Dec 2014
Investigating uncertainties in global gridded datasets of climate extremes
R. J. H. Dunn1, M. G. Donat2, and L. V. Alexander2 1Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB, UK
2ARC Centre of Excellence for Climate System Science and Climate Change Research Centre, UNSW, Sydney, NSW 2052, Australia
Abstract. We assess the effects of different methodological choices made during the construction of gridded data sets of climate extremes, focusing primarily on HadEX2. Using global land-surface time series of the indices and their coverage, as well as uncertainty maps, we show that the choices which have the greatest effect are those relating to the station network used or that drastically change the values for individual grid boxes. The latter are most affected by the number of stations required in or around a grid box and the gridding method used. Most parametric changes have a small impact, on global and on grid box scales, whereas structural changes to the methods or input station networks may have large effects. On grid box scales, trends in temperature indices are very robust to most choices, especially in areas which have high station density (e.g. North America, Europe and Asia). The precipitation indices, being less spatially correlated, can be more susceptible to methodological choices, but coherent changes are still clear in regions of high station density. Regional trends from all indices derived from areas with few stations should be treated with care. On a global scale, the linear trends over 1951–2010 from almost all choices fall within the 5–95th percentile range of trends from HadEX2. This demonstrates the robust nature of HadEX2 and related data sets to choices in the creation method.

Citation: Dunn, R. J. H., Donat, M. G., and Alexander, L. V.: Investigating uncertainties in global gridded datasets of climate extremes, Clim. Past, 10, 2171-2199, doi:10.5194/cp-10-2171-2014, 2014.
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Short summary
Observational data sets contain uncertainties, e.g. from the instrument accuracy, as well as from the fact that usually only a single method is used in processing. We have performed an assessment of the size of the uncertainties associated with choices in the method used. The largest effects come from changes which affect the station network or the gridding method used. However, for the temperature indices in places with many stations, these changes have little effect on the long-term behaviour.
Observational data sets contain uncertainties, e.g. from the instrument accuracy, as well as...
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