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

摘要

In this study we analyse the role of internal variability in regional climatesimulations through a comparison of two regional paleoclimate simulations forthe last millennium. They share the same external forcings and modelconfiguration, differing only in the initial condition used to run thedriving global model simulation. A comparison of these simulations allows usto study the role of internal variability in climate models at regionalscales, and how it affects the long-term evolution of climate variables suchas temperature and precipitation. The results indicate that, althoughtemperature is homogeneously sensitive to the effect of external forcings,the evolution of precipitation is more strongly governed by randomunpredictable internal dynamics. There are, however, some areas where the roleof internal variability is lower than expected, allowing precipitation torespond to the external forcings. In this respect, we explore the underlyingphysical mechanisms responsible for it. This study identifies areas,depending on the season, in which a direct comparison between modelsimulations of precipitation and climate reconstructions would be meaningful,but also other areas where good agreement between them should not beexpected even if both are perfect.