Extratropical circulation associated with Mediterranean droughts during the Last Millennium in CMIP5 simulations.

Knowing that internal climate variability is the principal driver of Mediterranean droughts during the last millennium, in this study, we investigate circulation patterns in the Euro-Atlantic domain associated with multi-year droughts over the Mediterranean region in CMIP5-PMIP3 and CESM-LME simulations. The focus is on the natural variability of droughts during 850–2005, thus excluding the anthropogenic trends from 1850 CE onward. The results re-confirm that Mediterranean drought occurrence during the last millennium is associated with internal variability. In terms of the temporal variability, all climate models exhibit a multi-decadal anti-phase occurrence of droughts between the western and eastern Mediterranean agreeing with some proxy records. This anti-phase occurrence of droughts can be explained by the dominant circulation patterns in each region: western Mediterranean droughts are dominated by a high-pressure system and ridge over central Europe and an NAO-like pattern, while eastern Mediterranean droughts are linked to positive pressure anomalies in the southern and eastern Mediterranean, negative NAO, negative EA and EA-WR-like patterns. However, these modes of climate variability are strongly model-dependent, i.e. each model has its preferred circulation patterns that occur more frequently during droughts, suggesting that the main drivers of droughts differ between the models. The models' preference is therefore a potential source of uncertainties in Mediterranean droughts in model-proxy comparison and may have implications for future climate projections. [ABSTRACT FROM AUTHOR]