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

Abstract

[1] 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. Citation: Kelley, C., M. Ting, R. Seager, and Y. Kushnir (2012), Mediterranean precipitation climatology, seasonal cycle, and trend as simulated by CMIP5,

Impact of large-scale circulation changes in the North Atlantic sector on the current and future Mediterranean winter hydroclimate

“…NAO-and EA-type), which impacts winter Mediterranean hydroclimate. Our analysis corroborates some of the previous studies, which highlight a dominant effect of the NAO pattern (Kelley et al 2012;Trigo et al 2004;Mariotti and Dell'Aquilla 2012). For example Kelley et al (2012) argued that past three decades of drying over the Mediterranean are to a large extent caused by the negative phase of the multidecadal NAO variations.…”

Extratropical cyclones and the projected decline of winter Mediterranean precipitation in the CMIP5 models

“…The ability of CMIP5 models to represent the Mediterranean hydrological cycle has been analysed in detail by Kelley et al (2012) and Seager et al (2014). These studies show that the CMIP5 models, on average, have a reasonable representation of the observed Mediterranean precipitation, evaporation and moisture fluxes in winter.…”

Causes of Robust Seasonal Land Precipitation Changes*

“…Internal climate variability may explain some of the discrepancies. Dai (2013) showed how internal variability could produce apparent trends in regional precipitation on multidecadal time scales in the southwest United States while Kelley et al (2012) show that the winter drying seen in the Mediterranean observations may be due to multidecadal variability with the radiatively forced signal only beginning to emerge from the natural variability. Regional precipitation changes will also be affected by even subtle shifts in atmospheric circulation.…”