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Calibrated multi-model ensemble summer temperature predictions over Italy

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Abstract

A statistical calibration scheme is applied to multi-model global seasonal ensemble reforecasts in order to predict the interannual variability of summer averaged surface maximum temperature over Italy. In some cases, this technique is shown to be able to improve the skill scores of the seasonal predictions during the last 35 years, with respect to the direct model output (DMO), using seasonal predictions initialised 1 month before the beginning of the season. It is shown that the presence of some skill in the DMO multi-model predictions is mostly due to the correct prediction of the observed secular trends in maximum temperature, and, partly, to the correct prediction of outliers, in particular, of the summer of 2003. At the same time, while the removal of trends produces a small reduction of skill in both the raw and calibrated predictions, the removal of outliers improves the performance of the calibration scheme. Once all trends and outliers are removed, the DMO predictions have no skill, while the calibrated predictions still present a detectable skill. The improvement introduced by the calibration are shown to be statistically significant by applying resampling techniques. It is shown that the reason of this partial success is linked to the fact that although the models present several shortcomings, some models can capture the existence of a weak large-scale signal, possibly linked with the presence of a summer teleconnection between the equatorial Pacific and Europe, with a spatial pattern substantially different from that associated with the temperature secular trend. The teleconnection is associated with a modulation of the quasi-stationary barotropic eddies in the Northern Hemisphere extra-tropics.

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Acknowledgments

We would like to thank Dr. F. Nerozzi and Dr. T. Diomede for useful discussions and two anonymous reviewers who helped to improve substantially the quality of the paper. The results here presented have been produced within the framework of the ECMWF Special Project SPIT-SPIA. The work of the authors has been partially funded by the European Commission’s 6th Framework Programme through the ENSEMBLES Project (contract GOCE-CT-2003-505539). One author has also been funded by the Spanish national project called RUCSS (RUCSS is funded by Spanish Ministerio de Economía y Competitividad under Contract CGL2010-20657), while the other has also been partially funded by the Italian National Civil Protection Agency and by the Italian Ministry of Agricultural Policy through the Agroscenari applied research programme.

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Authors and Affiliations

  1. ARPA-SIMC, Viale Silvani 6, 40122, Bologna, Italy

    V. Pavan

  2. Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, 08010, Barcelona, Spain

    F. J. Doblas-Reyes

  3. Institut Català de Ciències del Clima (IC3), Doctor Trueta 203, 08005, Barcelona, Spain

    F. J. Doblas-Reyes

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  1. V. Pavan
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  2. F. J. Doblas-Reyes
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Correspondence to V. Pavan.

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Pavan, V., Doblas-Reyes, F.J. Calibrated multi-model ensemble summer temperature predictions over Italy. Clim Dyn 41, 2115–2132 (2013). https://doi.org/10.1007/s00382-013-1869-7

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