Mediterranean precipitation climatology, seasonal cycle, and trend as simulated by CMIP5

Winter and summer Mediterranean precipitation climatology and trends since 1950 as simulated by the newest generation of global climate models, the Coupled Model Intercomparison Project phase 5 (CMIP5), are evaluated with respect to observations and the previous generation of models (CMIP3) used in the Intergovernmental Panel on Climate Change Fourth Assessment Report. Observed precipitation in the Mediterranean region is defined by wet winters and drier summers, and is characterized by substantial spatial and temporal variability. The observed drying trend since 1950 was predominantly due to winter drying, with very little contribution from the summer. However, in the CMIP5 multimodel mean, the precipitation trend since 1950 is evenly divided throughout the seasonal cycle. This may indicate that in observation, multidecadal internal variability, particularly that associated with the North Atlantic Oscillation (NAO), dominates the wintertime trend. An estimate of the observed externally forced trend shows that winter drying dominates in observations but the spatial patterns are grossly similar to the multimodel mean trend. The similarity is particularly robust in the eastern Mediterranean region, indicating a radiatively forced component being stronger there. Results of this study also reveal modest improvement for the CMIP5 multi-model ensemble in representation of the observed six month winter and summer climatology. The results of this study are important for assessment of model predictions of hydroclimate change in the Mediterranean region, often referred to as a "hotspot" of future subtropical drying.