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Projections of rainfall and stream flow in the Mediterranean and the Fertile Crescent of the Middle East are presented here for the end of the twenty-first century. Up until recently, this has not been possible due to the lack of observed data and atmospheric models with sufficient resolution. An innovative super-high-resolution (20-km) global climate model is employed, which properly reproduces the moisture fields of the present-day climate over the study area. The model projected that the Fertile Crescent will lose its current shape and may disappear altogether by the end of this century. The annual discharge of the Euphrates River will decrease by 29–73 %, as will the stream flow in the Jordan River . Thus countermeasures for water shortages will become much more difficult.

Detailed knowledge of sea-salt aerosol (SSA) space-time variations is essential for a deeper understanding of the process of SSA loading in the atmospheric boundary layer. In order to reproduce variability of SSA concentrations over the Mediterranean Sea, the regional DREAM-Salt model has been running daily at Tel-Aviv University since February 2006 (http://wind.tau.ac.il/salt-ina/salt.html). The model performance in producing accurate SSA forecasts over the Mediterranean Sea was evaluated using a 5-year record (2006–2010) of daily SSA mass concentration measurements at the island of Lampedusa. Model-vs.-measurement comparisons showed a distinct dependence of model performance on wind direction. On average, for wind direction from 30° to 300°, the model performance was quite acceptable. It was characterized by a relatively high correlation of over 0.65 and a rather small mean bias. For north winds (0°–30°, and 300°–360°), some discrepancy between modeled and measured SSA concentrations was observed. This was characterized by the model underestimation of SSA measurements and a rather low correlation between model data and measurements. Probably, for north winds, SSA production in the surf zone, located in the vicinity of the monitoring site, contributed to observed SSA concentrations.

This chapter discusses results of current and future-projected water cycle components over the Mediterranean region. Results are presented from an ensemble of CMIP3 multi-model simulations (here after referred to as Mariotti) and from the Meteorological Research Institute’s (MRI) 20 km grid global climate model. Referred to as CMIP3 results are surprisingly close to MRI. The projected mean annual change in the rate of precipitation (P) across the region (for sea and land), is projected to decrease by the end of the 21st century by −11% and −10%, respectively, for the MRI and Mariotti runs. Projected changes in evaporation (E) are +9.3% (sea) and −3.6% (land) for JMA runs, compared to +7.2% (sea) and −8.1% (land) in Mariotti’s study. However, no significant difference of the projected change in P–E over the sea body is found between these two studies. E over the eastern Mediterranean was projected to be higher than the western Mediterranean, but the P decrease was projected to be lower. The net moisture budget, P–E, shows that the eastern Mediterranean is projected to become even drier than the western Mediterranean. The river model projects significant decreases in water inflow to the Mediterranean of about −36% by the end of the 21st century in the MRI run (excluding the Nile). The Palmer Drought Severity Index (PDSI), which reflects the combined effects of precipitation and surface air temperature (Ts) changes, shows a progressive and substantial drying of Mediterranean land surface over this region since 1900 (−0.2 PDSI units/decade), consistent with a decrease in precipitation and an increase in Ts (not shown). The last section of this chapter reports on components of the hydrological cycle from five climate model projections for the Mediterranean region. Three of these models have an interactive Mediterranean Sea (MPI, ENEA, Meteo-France), and two are versions of the Met Office Hadley Centre regional model (HadRM3-MOSES2, HadRM3-MOSES1) with different land surface schemes. The focus of this section is upon changes in evapotranspiration, and how these changes could be important in controlling available renewable water resources (runoff). These r indicate that rainfall is projected to decline across large areas by over −20% in all of the models, although in the Meteo-France model the central part of the northern Mediterranean domain, ie. southern Italy and Greece, has areas of increase as well as decrease. In pockets of Turkey, the eastern Mediterranean, Italy and Spain, projections from the MPI, HadRM3-MOSES2, HadRM3-MOSES1 and ENEA models are for decreases in summer rainfall of −50% or more. Consistent with the global model projections, each of the five high-resolution models simulate increasing temperatures and decreasing evapotranspiration and precipitation for much of the Mediterranean region by the middle of this century. The strongest and most widespread reductions in precipitation are projected to occur in the spring and summer seasons, while reductions in evapotranspiration are greatest in summer.

A super-high resolution (20 km) global climate model data and Climate Research Unit (CRU) data were employed to investigate the seasonal precipitation regime over the Middle East, and the main research focus is on the orographic rainfall effects over a large part of Turkey by using these two different datasets.

Sea-salt aerosol (SSA) could influence the Earth’s weather and climate acting as cloud condensation nuclei. In spite of the importance of SSA effects on the Earth’s climate and weather, there were no measurements of sea-salt aerosols in the open sea. At Tel-Aviv University, the DREAM-Salt prediction system has been producing daily forecasts of 3-D distribution of sea-salt aerosol concentrations over the Mediterranean model domain 20 W–45E, 15 N–50 N (http://wind.tau.ac.il/salt-ina/salt.html). In order to evaluate the model performance in the open sea, daily modeled sea-salt aerosol concentrations were compared directly with sea-salt ground-based measurements taken at the tiny island of Lampedusa, in the Central Mediterranean. In order to further test the robustness of the model, the model performance over the open sea was indirectly verified by comparing modeled SSA concentrations with wave height measurements collected by the ODAS Italia 1 buoy. Model-vs.-measurement comparisons show that the model is capable of producing realistic SSA concentrations and their day-to-day variations over the open sea, in accordance with observed wave height and wind speed.

The Po Valley in Northern Italy is frequently affected by high PM10 concentrations, where both natural and anthropogenic sources play a significant role. This work was aimed at giving a proper account of the contribution of Saharan dust to air quality in the Po Valley. This was carried out by improving the boundary conditions of the mesoscale 3D deterministic Transport Chemical Aerosol Model (TCAM) on large-scale transport of Saharan dust, daily predicted over the Mediterranean region. A case study of the integration of the TCAM and DREAM models was implemented over the Po Valley. The results show that the use of improved boundary conditions leads TCAM to better performances, both in terms of correlation and mean errors: TCAM was able to more accurately reproduce high PM10 concentrations observed in the Po Valley during particular dust events.

Climate change trends over the southern east-Europe are evaluated according to results of a climate simulation experiment with the ICTP RegCM3 regional climate model driven from the lateral boundaries by results of ECHAM5/MPI-OM1 transient climate simulation from 1960 to 2060 (SRES A1B emission scenario after 2001). The trends projected include – precipitation: winter and spring – rise over the central east-Europe and drop over the eastern Mediterranean region, summer-autumn – drop over east-Europe and northern eastern-Mediterranean, rise over the Middle East (especially in autumn); 2-m air temperature: winter and spring – rise over the whole region with a maximum over its eastern and north-eastern (especially) and south-eastern parts, summer – rise with a maximum over the Middle East and minimum over north-eastern part, autumn – rise with maximum over the Caspian, Black Seas and northern areas of the European Territory of Russia.

3D-dust distributions, daily predicted by the Tel Aviv University Weather Research Center, are used by the Ministry of Environmental Protection to distinguish between natural and anthropogenic aerosols. Two different dust prediction systems were used to perform a sensitivity experiment and to compare the accuracy of the models. The first one was the original DREAM model with four dust particle size classes (0.7, 6.1, 18.0 and 38.0 μm); only the first two classes have a radius less than 10 μm and can be used in comparisons with PM10 measurements. The second model used was the modified DREAM model (DREAM-8) with a more detailed set of dust particle size classes with a radius of between 0.1 and ∼7 μm (0.15, 0.25, 0.45, 0.78, 1.3, 2.2, 3.8, and 7.1 μm). The sensitivity experiment was carried out by using a quantitative comparison between PM10 measurements of surface dust concentrations and those predicted by models, for the high dust activity season in Israel, from February to June 2006. Quantitative comparisons showed that the use of eight particle size classes including four less than 1 μm in dust modelling, instead of only two classes, improves dust forecasts.

A model was developed for pollutant dispersion from a point source simulating the Hadera (Israel) power plant stack. The model is based on the NCAR mesoscale meteorological MM4 model that provides the wind fields and coefficients of turbulent diffusion. The model was implemented using an implicit numerical scheme with changing directions. A comparison between the model calculations and an analytical solution for the advection-diffusion equation shows good agreement. Relatively low numerical diffusion of the adopted advection scheme was noted. Results for the hilly region of central Israel are presented for a summer case.

The effects of sea-breeze interactions with synoptic forcing on the PBL height over complex terrain are investigated through the use of a 3-D mesoscale numerical model. Two of the results are as follows. First, steep PBL height gradients — order of 1500 m over a grid interval of 10 km — are associated with the sea-breeze front and are enhanced by the topography. Second, a significant horizontal shift in the maximum PBL height relative to the mountains, is induced by a corresponding displacement of the thermal ridge due to the mountains, in the presence of large scale flow.

In a first theoretical study, the reasons for anticlockwise rotation (clockwise rotation in the southern hemisphere) of the wind hodograph in the boundary layer are investigated. As observations of wind hodographs show two kinds of anti-clockwise rotation (ACR, in brevity) one frequently observed, which is highly irregular with partly ACR and the other with clear ACR, two methods have been applied. At first two-dimensional nonlinear model (described by Alpert et al., 1982) including sea-land breeze as well as a mountain reveal at the lee of the mountain partly ACR. By analyzing the different terms in the equation for the wind vector rotation (see Neumann, 1977) it is shown that usually the pressure-gradient term is the leading one and the advection term is very small. But the latter becomes important in case of ACR. Secondly, a linear model is solved analytically showing that inclusion of a rotating heating forcing in the ACR sense generates clear ACR.