Internal and external variability in regional simulations of the Iberian Peninsula climate over the last millennium

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In this study we analyse the role of internal variability in regional climate simulations through a comparison of two regional paleoclimate simulations for the last millennium. They share the same external forcings and model configuration, differing only in the initial condition used to run the driving global model simulation. A comparison of these simulations allows us to study the role of internal variability in climate models at regional scales, and how it affects the long-term evolution of climate variables such as temperature and precipitation. The results indicate that, although temperature is homogeneously sensitive to the effect of external forcings, the evolution of precipitation is more strongly governed by random unpredictable internal dynamics. There are, however, some areas where the role of internal variability is lower than expected, allowing precipitation to respond to the external forcings. In this respect, we explore the underlying physical mechanisms responsible for it. This study identifies areas, depending on the season, in which a direct comparison between model simulations of precipitation and climate reconstructions would be meaningful, but also other areas where good agreement between them should not be expected even if both are perfect.
© Author(s) 2012. This work is distributed under the Creative Commons Attribution 3.0 License. This work was funded by the Spanish Ministry of the Environment (project SALVA-SINOVAS, Ref. 200800050083542) and the Spanish Ministry of Science and Technology (projects SPEQMORE-CGL2008-06558-C02-02/CLI and SPEQTRES-CGL2011-29672-C02-02). The authors also gratefully acknowledge funding from the Euro-Mediterranean Institute of Water (IEA). J. J. Gómez Navarro thanks the Spanish Ministry of Education for his Doctoral scholarship (AP2006-04100). The work by E. Zorita is embedded in the EU-Project Millennium European Climate. Thanks to Elena Bustamante for the stimulating discussions.
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