Abstract
Abstract. We analyse the spatial expression of seasonal climates of the Mediterranean and northern Africa in pre-industrial (piControl) and mid-Holocene (midHolocene, 6 yr BP) simulations from the fifth phase of the Coupled Model Intercomparison Project (CMIP5). Modern observations show four distinct precipitation regimes characterized by differences in the seasonal distribution and total amount of precipitation: an equatorial band characterized by a double peak in rainfall, the monsoon zone characterized by summer rainfall, the desert characterized by low seasonality and total precipitation, and the Mediterranean zone characterized by summer drought. Most models correctly simulate the position of the Mediterranean and the equatorial climates in the piControl simulations, but overestimate the extent of monsoon influence and underestimate the extent of desert. However, most models fail to reproduce the amount of precipitation in each zone. Model biases in the simulated magnitude of precipitation are unrelated to whether the models reproduce the correct spatial patterns of each regime. In the midHolocene, the models simulate a reduction in winter rainfall in the equatorial zone, and a northward expansion of the monsoon with a significant increase in summer and autumn rainfall. Precipitation is slightly increased in the desert, mainly in summer and autumn, with northward expansion of the monsoon. Changes in the Mediterranean are small, although there is an increase in spring precipitation consistent with palaeo-observations of increased growing-season rainfall. Comparison with reconstructions shows most models underestimate the mid-Holocene changes in annual precipitation, except in the equatorial zone. Biases in the piControl have only a limited influence on midHolocene anomalies in ocean–atmosphere models; carbon-cycle models show no relationship between piControl bias and midHolocene anomalies. Biases in the prediction of the midHolocene monsoon expansion are unrelated to how well the models simulate changes in Mediterranean climate.
Highlights
The Mediterranean area, including southern Europe and northern Africa, is characterized today by a highly seasonal climate with summer drought and a wet season between October and March (Mehta and Yang, 2008)
Modern observations show four distinct precipitation regimes characterized by differences in the seasonal distribution and total amount of precipitation: an equatorial band characterized by a double peak in rainfall, the monsoon zone characterized by summer rainfall, the desert characterized by low seasonality and total precipitation, and the Mediterranean zone characterized by summer drought
First we identify the spatial extent of each precipitation regime in the midHolocene simulations and compare this with the spatial extent shown in the piControl simulation of the same model
Summary
The Mediterranean area, including southern Europe and northern Africa, is characterized today by a highly seasonal climate with summer drought and a wet season between October and March (Mehta and Yang, 2008). The generally low precipitation and marked seasonality gives rise to drought-adapted, sclerophyllous vegetation that is highly susceptible to wildfire during the dry season (Moreira et al, 2011). The Mediterranean region has experienced warming and increased drought in recent years (Camuffo et al, 2010; Hoerling et al, 2012; European Environment Agency, 2012) and has been identified as highly vulnerable to future climate changes (Giorgi, 2006). Model projections indicate large increases in temperatures and a reduction in mean annual precipitation Meehl et al, 2007; Giorgi and Lionello, 2008; Nikulin et al, 2011), both of which would lead to large changes in vegetation cover and exacerbate wildfires (Amatulli et al, 2013). Measures of how well the models simulate modern climate do not provide a measure of whether
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