Christos Giannakopoulos

Climate change and impacts in the Eastern Mediterranean and the Middle East.

The Eastern Mediterranean and the Middle East (EMME) are likely to be greatly affected by climate change, associated with increases in the frequency and intensity of droughts and hot weather conditions. Since the region is diverse and extreme climate conditions already common, the impacts will be disproportional. We have analyzed long-term meteorological datasets along with regional climate model projections for the 21st century, based on the intermediate IPCC SRES scenario A1B. This suggests a continual, gradual and relatively strong warming of about 3.5–7°C between the 1961–1990 reference period and the period 2070–2099. Daytime maximum temperatures appear to increase most rapidly in the northern part of the region, i.e. the Balkan Peninsula and Turkey. Hot summer conditions that rarely occurred in the reference period may become the norm by the middle and the end of the 21st century. Projected precipitation changes are quite variable. Annual precipitation is expected to decrease in the southern Europe – Turkey region and the Levant, whereas in the Arabian Gulf area it may increase. In the former region rainfall is actually expected to increase in winter, while decreasing in spring and summer, with a substantial increase of the number of days without rainfall. Anticipated regional impacts of climate change include heat stress, associated with poor air quality in the urban environment, and increasing scarcity of fresh water in the Levant.

Validation and intercomparison of wet and dry deposition schemes using 210Pb in a global three-dimensional off-line chemical transport model

We have used 210 Pb, a tracer originating from the radioactive decay of 222 Rn emitted from soils, to validate different wet and dry deposition schemes in our global three-dimensional off-line chemical transport model, TOMCAT. We have tested two different parameterizations for the dry deposition, one with the turbulent exchange in the boundary layer and one without. When dry deposition is linked to the boundary layer scheme, the model shows the ability to resolve shallow mixing depths in winter with enhanced lifetimes and concentrations of surface aerosol. Three conceptually different wet deposition schemes have been implemented and tested in TOMCAT. In the first, where wet removal is assumed to be proportional to the local gradient of the specific humidity, the model has a global mean bias for the surface concentrations of -40%. Using this scheme, the observed surface concentrations are seriously underpredicted, and most of the aerosol burden is scavenged within the boundary layer. In the second scheme, where scavenging is parameterized proportional to the model-derived total precipitation rate (large scale and convective), the model exhibits a +26% bias. The concentrations are overpredicted, especially in continental areas as this scheme fails to capture the coupling between vertical transport and rainout. In the third scheme, wet removal is coupled with the vertical transport inside convective clouds. The model then shows the best performance with only a -4% bias for the concentrations. Furthermore, other regional discrepancies between model and observations point to a variability in 222 Rn emissions, which was not taken into account with our simple 222 Rn emission scenario, and also to anomalies in our model-derived precipitation rate. The aerosol residence times are realistic only when the wet removal schemes use the precipitation rate rather than the specific humidity. The dry subtropical and polar regions can be captured with lifetimes at 500 hPa of more than 50 days whereas in regions of high precipitation the lifetimes are less than 5 days.

Model projected heat extremes and air pollution in the eastern Mediterranean and Middle East in the twenty-first century

The eastern Mediterranean and Middle East, a region with diverse socioeconomic and cultural identities, is exposed to strong climatic gradients between its temperate north and arid south. Model projections of the twenty-first century indicate increasing hot weather extremes and decreasing rainfall. We present model results, which suggest that across the Balkan Peninsula and Turkey climate change is particularly rapid, and especially summer temperatures are expected to increase strongly. Temperature rise can be amplified by the depletion of soil moisture, which limits evaporative cooling, prompted by the waning of large-scale weather systems that generate rain. Very hot summers that occurred only rarely in the recent past are projected to become common by the middle and the end of the century. Throughout the region, the annual number of heat wave days may increase drastically. Furthermore, conditions in the region are conducive for photochemical air pollution. Our model projections suggest strongly increasing ozone formation, a confounding health risk factor particularly in urban areas. This adds to the high concentrations of aerosol particles from natural (desert dust) and anthropogenic sources. The heat extremes may have strong impacts, especially in the Middle East where environmental stresses are plentiful.

The meteorological conditions associated with extreme fire risk in Italy and Greece: relevance to climate model studies

The meteorological conditions associated with elevated and extreme long- and short-timescale forest fire risk are investigated by validating and diagnosing the Canadian Fire Weather Index (FWI) in the context of Tuscany in Italy, and Thessaloniki, Athens and Heraklion in Greece. The aim is to provide information to assist diagnosing experiments that use output from climate models to calculate FWI values. Links are made from fire risk to the widely used FWI, and then to the underlying meteorology, complementing other more complex fire risk model studies. First, the information about Mediterranean fire risk provided by the FWI is assessed by comparing the observed number of fires per day with FWI values based on the locally observed meteorology. This shows that the FWI provides some relatively consistent information for different locations, and suggests useful FWI thresholds indicating elevated and extreme fire risk. Then, the FWI system is split according to contributions from long- and short-timescale components, in a different way than usually adopted in the literature. Using the FWI thresholds suggested above, the long- and short-timescale meteorological conditions causing elevated and extreme FWI values are diagnosed. The results may help studies that investigate what aspects of projected climate change drive changes in fire weather risk, compare fire risk calculations from different climate models, or assess how climate models can be improved to provide better fire risk projections.

The Impact of the Eastern Mediterranean Teleconnection Pattern on the Mediterranean Climate

Abstract The objective of this study is to investigate the impact of the eastern Mediterranean teleconnection pattern (EMP) on the present and future climate of the eastern Mediterranean during winter. For the present climate, daily precipitation and maximum and minimum surface temperature station data are employed for the period of 1958–2003. For the future climate, datasets of the same parameters are derived from the Hadley Centre Regional Climatic Model (HadRM3P) for the period of 2070–2100, using two Intergovernmental Panel on Climate Change (IPCC) emission scenarios for the evolvement of the future atmospheric concentrations of greenhouse gases. The investigation of the impact was based on the regularized canonical correlation analysis (RCCA), while qualitative estimations were performed for each phase of the pattern. It was found that the pattern indeed affects the mean winter patterns of temperature, precipitation, and their extreme events with inverse impacts between the two phases. More specifica...

Is the ozone climate penalty robust in Europe

Ozone air pollution is identified as one of the main threats bearing upon human health and ecosystems, with 25 000 deaths in 2005 attributed to surface ozone in Europe (IIASA 2013 TSAP Report #10). In addition, there is a concern that climate change could negate ozone pollution mitigation strategies, making them insufficient over the long run and jeopardising chances to meet the long term objective set by the European Union Directive of 2008 (Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008) (60 ppbv, daily maximum). This effect has been termed the ozone climate penalty. One way of assessing this climate penalty is by driving chemistry-transport models with future climate projections while holding the ozone precursor emissions constant (although the climate penalty may also be influenced by changes in emission of precursors). Here we present an analysis of the robustness of the climate penalty in Europe across time periods and scenarios by analysing the databases underlying 11 articles published on the topic since 2007, i.e. a total of 25 model projections. This substantial body of literature has never been explored to assess the uncertainty and robustness of the climate ozone penalty because of the use of different scenarios, time periods and ozone metrics. Despite the variability of model design and setup in this database of 25 model projection, the present meta-analysis demonstrates the significance and robustness of the impact of climate change on European surface ozone with a latitudinal gradient from a penalty bearing upon large parts of continental Europe and a benefit over the North Atlantic region of the domain. Future climate scenarios present a penalty for summertime (JJA) surface ozone by the end of the century (2071–2100) of at most 5 ppbv. Over European land surfaces, the 95% confidence interval of JJA ozone change is [0.44; 0.64] and [0.99; 1.50] ppbv for the 2041–2070 and 2071–2100 time windows, respectively.

Study of CO surface pollution in Europe based on observations and nested-grid applications of GEOS-CHEM global chemical transport model.

Carbon monoxide (CO) is studied over Europe for 2001 using measurements from 31 rural-background stations and the nested-grid application of the global CTM GEOS-CHEM. The model reveals lowest (highest) biases in warm (cold) periods, tracking observations in most cases more closely than the global model. The role of CO production and destruction processes and the atmospheric conditions are investigated. A rotated Principal Component Analysis is applied to all stations, based on daily CO modelled concentrations in 2001, yielding three principal components (PCs) with stations of common characteristics. CO concentrations are studied for these groups in relation to the circulation patterns prevailing over Europe in 2001, at mean sea level and 850 hPa. The nested-grid model improves results in comparison to those calculated by the global model by up to ∼22% for first principal component subregion, where emissions are high and elevation is low. Improvement reaches∼17 and∼7%, respectively, for second and third principal component subregions, where emissions are lower and altitudes are higher. Better performance is achieved for patterns associated with westerly flow, whereas poor skills are revealed during stagnant conditions. During pollution events, the nesting model’s ability in capturing CO surface concentrations improves by up to ∼40% in comparison to the global simulation.

The role of blocking in the summer 2014 collapse of Etesians over the eastern Mediterranean

We investigate the dynamical harbingers leading to the remarkable summer 2014 decline of the northerly flow (Etesians) over the eastern Mediterranean. From mid-July to mid-August four distinct episodes of unseasonal southerly flow were identified and associated with upper level troughs over central Europe and the Balkans. These features developed as repeated episodes of wave breaking, leading to blocking over Europe in July, and triggered equatorward streamers of high potential vorticity. During July a twofold increase in blocking occurrence against climatology was identified over parts of Europe and was part of a five-wave hemispheric pattern featuring abundant high-latitude blocking also over central Asia, the central Pacific, and western Atlantic. Overall, the frequent European blocking resulted in the southward displacement of the midlatitude storm track toward the Balkans and the relaxation of the traditional sharp east-west pressure gradient that triggered the collapse of Etesians. The bifurcation of the midlatitude jet caused by blocking led to the intensification of the westerly flow over the Mediterranean, accompanying the passing disturbances farther to the north, which combined with the weak Etesians resulting in a dramatic modification of the large-scale circulation over the Mediterranean Basin.

A three‐dimensional modeling study of the correlations of 210Pb with HNO3 and peroxyacetylnitrate (PAN) at remote oceanic sites

We have used 210 Pb, a tracer originating from the radioactive decay of 222 Rn emitted from soils, to show that tracers not affected by complex chemical reactions can provide a strong indication of the origin of air masses in the remote oceanic atmosphere and can help us understand the behavior of species which are affected by chemistry. Using our three-dimensional off-line chemical transport model (CTM), TOMCAT, we show that 210 Pb tends to covary with altitude with HNO 3 and peroxyacetylnitrate (PAN) at remote oceanic areas, suggesting the importance of transport for insoluble species (in our case 222 Rn and NO x ) that are able to escape deep convective scavenging and travel long distances before being transformed to soluble species (here 210 Pb and HNO 3 ). Near the continental coast, especially in the lower part of the troposphere, model HNO 3 levels are large, evident of the continental influence. PAN and 10 Pb levels are small. This indicates that 222 Rn has not yet decayed to 210 Pb and also PAN formation is not favored due to higher temperatures near the surface. Therefore, in these young air masses, only PAN and 210 Pb correlate, both having low values. Higher up, in the middle to upper troposphere, our modeling study shows that HNO 3 and 210 Pb tend to correlate, since in these relatively older air masses there was sufficient time for 210 Pb formation.

An efficient chemical systems modelling approach

Abstract Systems of stiff chemical reactions are often associated with atmospheric chemistry modelling, which plays a very important role in the studies of stratospheric ozone depletion, tropospheric air pollution problems, and future chemistry-climate feedbacks and interactions. This paper revisits an open-source stiff system solver SVODE and presents its efficient use in modelling different levels of complexity of a range of chemical systems. The chemical systems discussed here are the Lotka–Volterra (predator–prey) model, the Brusselator model, the Oregonator model, and the Lorenz model. The first two models consist of two variables, while the remaining two models consist of three variables. Finally, an application of this modelling approach to a generalised organic/NOx mechanism for characterising air pollution development is presented. Since the SVODE is an open-source code, and the simulations were run on a Linux PC (with g77 compiler), all results discussed in this paper can be easily reproduced. Most importantly, the approach shown here can be readily extended to other larger scale applications such as the three-dimensional air pollution modelling.