Regional climate modeling of the mediterranean and the Iberian Peninsula climate variability

Resum

The Mediterranean region is characterized by intense air-sea interaction and dominant high and low pressure systems that results in a complex and strongly seasonal climate system. Future climate projections performed with increasing concentrations of greenhouse gases, have revealed this region to be one of the climate change “hot spots” of the 21st century. The vulnerability of the Mediterranean climate system to the ongoing climate change, and the crucial role that air-sea interaction plays in this region, have motived the European scientific community at coordinating the climate modeling community towards the development of fully coupled regional climate models. This common effort has been formalized under the Med-CORDEX project, which primary goals are to improve understanding of past climate variability and trends, and to provide more accurate and reliable future projections. Part of this thesis is a contribution to the Med-CORDEX project. In this thesis work we use multi-model ensembles of regional climate models (RCMs) to study the climate variability of the Mediterranean Sea and of the Iberian Peninsula(IP). Despite its relatively small extension, the IP, which is influenced by both Atlantic and Mediterranean basins, presents a large variety of climates. Since the IP climate variability is linked to the Mediterranean Climate, an integrated study of the two regions results in an excellent framework to investigate the physical mechanisms responsible for the observed climate in these regions. The research projects that produced the RCM multi-model ensembles used in this thesis work, have produced both present- and future-time simulations. However, in this manuscript we present only the results of the present-time model outputs. First, we focused on the Mediterranean basin climate variability, and in particular on the variability of its air-sea heat fluxes, which affect several climate processes controlling the Mediterranean climate. These include the winter formation of deep waters, which is the primary driver of the Mediterranean Sea overturning circulation. Combing models and observations, we were able to connect the two leading modes of air-sea heat flux variability with large-scale atmospheric teleconnection patterns. Also, by performing a budget analysis, we were able to explain the physical mechanism linking these teleconnection patterns with the airsea heat flux variability. Once assessed the heat fluxes variability of the Mediterranean Sea, we connected this to the climate variability of the IP using a 4-model ensemble of RCM. In particular, we investigated mean fields of basic atmospheric parameters and the interannual variability of temperature and precipitation extremes. We assessed the spatial distribution of extreme events statistics and, comparing the four RCMs, we identified regions with high and low internal variability as well as with large bias among the models.