The atmosphere is a chaotic system displaying recurrent large-scale configurations. Recent developments in dynamical systems theory allow us to describe these configurations in terms of the local dimension—a proxy for the active number of degrees of freedom—and persistence in phase space, which can be interpreted as persistence in time. These properties provide information on the intrinsic predictability of an atmospheric state. Here, this technique is applied to atmospheric configurations in the eastern Mediterranean, grouped into synoptic classifications (SCs). It is shown that local dimension and persistence, derived from reanalysis and CMIP5 models’ daily sea-level pressure fields, can serve as an extremely informative qualitative method for evaluating the predictability of the different SCs. These metrics, combined with the SC transitional probability approach, may be a valuable complement to operational weather forecasts and effective tools for climate model evaluation. This new perspective can be extended to other geographical regions.
The semi‐objective synoptic classification was used to investigate future changes in the occurrence of EM synoptic types, with an emphasis on Cyprus Lows (CL). A significant reduction in CL occurrence is found towards the end of the 21st century. The reductions in CLs are accompanied by an increase in the frequencies of Red Sea Troughs and Highs in winter. The predicted changes in the occurrence of various synoptic types will lead to a more accurate forecast of climatic hazards. The eight CMIP5 models average ensemble of winter (DJF) synoptic group frequencies (in %: Lows, Cyprus Lows; RST, Red Sea Troughs; PT, Persian Troughs; H, Highs) for the historic (1986–2005), mid‐century (2046–2065) and end of the century (2081–2100) periods for RCP4.5 and RCP8.5 scenarios. The NCEP synoptic classification is shown for reference.
The eastern Mediterranean (EM) is expected to be influenced by climate changes that will significantly affect ecosystems, human health and socio‐economic aspects. One aspect of climate change in this vulnerable area is the length of the seasons, especially that of the rainy winter season against the warm and dry summer. Here, the synoptic seasons’ definition of Alpert, Osetinsky, Ziv, and Shafir (2004a) was applied to an ensemble of eight Coupled Model Inter‐Comparison Project phase 5 (CMIP5) models, under RCP8.5 and RCP4.5 scenarios, to predict the changes in the lengths of EM seasons during the 21st century. It is shown that the ensemble adequately represents the annual cycle of the main synoptic systems over the EM. The analysis further suggests that at the end of the 21st century, the duration of the synoptic summer, characterized by the occurrence of the Persian Trough, is expected to be lengthened by 49%, while the synoptic winter, characterized by the occurrence of the Cyprus Low, is expected to be shortened by 56% under the RCP8.5 scenario. This may lead to substantial changes in the hydrological regime and water resources, reduce the potential of dry farming, increase the risk of fires and air pollution and change the timing of seasonal health hazards.
High‐resolution climate projections over Israel (about 8 km) have been obtained with the regional model COSMO‐CLM, nested into the CORDEX‐MENA simulations at 25 km resolution. This simulation provides high‐resolution spatial variability of total precipitation and precipitation intensity. Projections are presented not only in terms of average properties, but also using a subset of extreme temperature and precipitation indices from the standard Expert Team on Climate Change Detection and Indices (ETCCDI) for the period 2041–2070 with respect to 1981–2010 (RCP4.5). A general increase in seasonal mean temperature is projected throughout the domain with peaks of ~2.5 °C, especially in winter and autumn. Extreme temperature indices show increases, larger in the minimum than in the maximum temperatures. Regarding total seasonal precipitation, decreases were found in the north and central Mediterranean climate parts of Israel, with reductions reaching ~40%, and increases of the same percentage in the most southern arid parts during winter and spring. An increase in precipitation intensity is shown mostly for the southern arid part of the region, with some indications of extremity also in the north. This spatial pattern probably results from a decrease in cyclones’ occurrences, which mainly influences the northern and central parts of Israel, and an increase in convective activity in the south. The outcome of this study can serve as a basis for priority setting and policy formulation towards better climate adaptation.
An evaluation of 23 models, participating in the Coupled Model Inter‐comparison Project phase 5 (CMIP5), in representing extreme precipitation indices (EPI), over the Eastern Mediterranean (EM) and the Fertile Crescent (FC), was performed. The models ensemble was then used to predict the EPIs evolution in the 21st century under (Representative Concentration Pathway, RCP) RCP4.5 and RCP8.5 scenarios. Models' performance was determined with respect to gridded precipitation observations from the APHRODITE project. The ensemble mean was found to perform relatively well in capturing the EM steep precipitation gradient, the FC structure and the EPI trends in the observations period (1970–2000). Over the EM, CMIP5 models agree on a future decrease in the following three EPIs; total precipitation (TP), consecutive wet days, and number of wet days by the values of 20–35%, 10–20%, and 20–35%, respectively. In the FC, extremely wet days (P95) are expected to increase by approximately 25%, except for the south eastern coasts of the Mediterranean Sea, which show significant decreases in P95, particularly for RCP8.5 and at the end of the 21st century. Hence, while TP is expected to decrease, extreme precipitation is expected to increase, at least for the north‐eastern part of the FC. This will significantly influence agriculture and floods' potential in a region already suffering from political unrest. The changes in EPIs are related to changes in the synoptic patterns over the EM, especially the predicted changes in cyclones frequency and intensity in the 21st century, due to changes in storm tracks governed by the phase of the North Atlantic Oscillation and the expected expansion of the Hadley Cell towards the poles in a warmer climate.
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