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The study presents a time-dependent analysis of threats from man-made climate change at 244 UNESCO cultural and natural heritage sites in the Mediterranean. The hazards in our research are estimated by indices based on extremes of heat, fire weather conditions, heavy rainfall days, frost days, changes in mean sea level and aridity at each site. These indices were calculated from regional EUROCORDEX simulations, cover the period 1971–2100 and refer to two IPCC emission scenarios, namely RCP4.5 and RCP8.5. A combined threat index was next calculated, as explained in the text, together with its synergy with local exposure geophysical threats, such as seismicity, topography and proximity to forests and seas. All indices related to man-made climate change show an overall increasing trend from present to the end of the twenty-first century. Some of these increasing trends are intensified after the 2030s and 2040s, except for the case of the days with frost. As the global warming evolves, in both IPCC scenarios studied, the combined threat to the majority of UNESCO sites studied increases. Notable is the amplification of the threat at sites vulnerable to seismic activity and to other local or regional topography and geophysical regional characteristics. Our conclusion is that the majority of heritage sites in the Mediterranean are vulnerable to an increasing rate of threats from man-made global warming and extreme events. Seismic activity is magnifying these threats only at the sites in which that additional hazard applies. Based on the proposed combined threat index, for the worst-case scenario (RCP8.5) 35 monument sites fall within the “high hazard” and 12 sites fall under the category “extreme hazard”.

The Copernicus Atmosphere Monitoring Service (CAMS) is operationally providing forecast and reanalysis products of air quality and atmospheric composition. In this article, we present an extended evaluation of the CAMS global reanalysis data set of four reactive gases, namely, ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), and formaldehyde (HCHO), using multiple independent observations. Our results show that the CAMS model system mostly provides a stable and accurate representation of the global distribution of reactive gases over time. Our findings highlight the crucial impact of satellite data assimilation and emissions, investigated through comparison with a model run without assimilated data. Stratospheric and tropospheric O3 are mostly well constrained by the data assimilation, except over Antarctica after 2012/2013 due to changes in the assimilated data. Challenges remain for O3 in the Tropics and high-latitude regions during winter and spring. At the surface and for short-lived species (NO2), data assimilation is less effective. Total column CO in the CAMS reanalysis is well constrained by the assimilated satellite data. The control run, however, shows large overestimations of total column CO in the Southern Hemisphere and larger year-to-year variability in all regions. Concerning the long-term stability of the CAMS model, we note drifts in the time series of biases for surface O3 and CO in the Northern midlatitudes and Tropics and for NO2 over East Asia, which point to biased emissions. Compared to the previous Monitoring Atmospheric Composition and Climate reanalysis, changes in the CAMS chemistry module and assimilation system helped to reduce biases and enhance the long-term temporal consistency of model results for the CAMS reanalysis.

The Battle of Salamis in 480 B.C. is one of the most important naval battles of all times. This work examines in detail the climatically prevailing weather conditions during the Persian invasion in Greece. We perform a climatological analysis of the wind regime in the narrow straits of Salamis, where this historic battle took place, based on available station measurements, reanalysis and modeling simulations (ERA5, WRF) spanning through the period of 1960&ndash, 2019. Our results are compared to ancient sources before and during the course of the conflict and can be summarized as follows: (i) Our climatological station measurements and model runs describing the prevailing winds in the area of interest are consistent with the eyewitness descriptions reported by ancient historians and (ii) The ancient Greeks and particularly Themistocles must have been aware of the local wind climatology since their strategic plan was carefully designed and implemented to take advantage of the diurnal wind variation. The combination of northwest wind during the night and early morning, converging with a south sea breeze after 10:00 A.M., formed a &ldquo, pincer&rdquo, that aided the Greeks at the beginning of the clash in the morning, while it brought turmoil to the Persian fleet and prevented them to escape to the open sea in the early afternoon hours.

Spectral UV records of solar irradiance at stations over Europe, Canada, and Japan were used to study long-term trends at 307.5 nm for a 25-year period, from 1992 to 2016. Ground-based measurements of total ozone, as well as satellite measurements of the Aerosol Index, the Total Cloud Cover and the surface reflectivity were also used in order to attribute the estimated changes of the UV to the corresponding changes of these factors. The present study shows that over the Northern Hemisphere, the long-term changes in UV-B radiation reaching the Earth’s surface vary significantly over different locations, and that the main drivers of these variations are changes in aerosols and total ozone. At high latitudes, part of the observed changes may also be attributed to changes in the surface reflectivity. Over Japan, the UV-B irradiance at 307.5 nm has increased significantly by 3%/decade during the past 25 years, possibly due to the corresponding significant decrease of its absorption by aerosols. It was found that the greatest part of this increase took place before the mid-2000s. The only European station, over which UV radiation increases significantly, is that of Thessaloniki, Greece. Analysis of the clear-sky irradiance for the particular station shows increasing irradiance at 307.5 nm by 3.5%/decade during the entire period of study, with an increasing rate of change during the last decade, possibly again due to the decreasing absorption by aerosols.

The impact of climate change on cotton and maize was estimated on the basis of three IPCC Emission Scenarios (A1B, A2, B2) for seven main agronomic areas during three periods, 1961–1990, 2021–2050 and 2071–2100. All climate models were assessed for their ability to identify the yield differences through the standardized discriminant function coefficients. Discriminant analysis was performed for each period. For cotton, using the A1B scenario, areas of Western Greece exhibited the most favourable results in terms of yield increase, compared to other regions, ranging up to the maximum value of +24%. This tendency became more pronounced towards the end of the century reaching an increase of +31%. In the A2 scenario, all the areas had a positive impact on their yield change rising up to 30% in areas of central Greece. A positive change for all regions was observed for scenario B2 ranging from +10% to +25%. In maize, the scenario A1B produced small changes in yields, not exceeding 5%. For A2 scenario, yield change varied from −5.7% to +3.6%. Scenario B2 gave more optimistic estimates of yield changes towards the end of the century, in some cases exceeding 5%.

In this paper, we compare model calculations of ozone profiles and their variability for the period 1998 to 2016 with satellite and lidar profiles at five ground-based stations. Under the investigation is the temporal impact of the stratospheric halogen reduction (chemical processes) and increase in greenhouse gases (i.e., global warming) on stratospheric ozone changes. Attention is given to the effect of greenhouse gases on ultraviolet-B radiation at ground level. Our chemistry transport and chemistry climate models (Oslo CTM3 and EMAC CCM) indicate that (a) the effect of halogen reduction is maximized in ozone recovery at 1&ndash, 7 hPa and observed at all lidar stations, and (b) significant impact of greenhouse gases on stratospheric ozone recovery is predicted after the year 2050. Our study indicates that solar ultraviolet-B irradiance that produces DNA damage would increase after the year 2050 by +1.3% per decade. Such change in the model is driven by a significant decrease in cloud cover due to the evolution of greenhouse gases in the future and an insignificant trend in total ozone. If our estimates prove to be true, then it is likely that the process of climate change will overwhelm the effect of ozone recovery on UV-B irradiance in midlatitudes.

Review of the existing bibliography shows that the direction and magnitude of the long-term trends of UV irradiance, and their main drivers, vary significantly throughout Europe. Analysis of total ozone and spectral UV data recorded at four European stations during 1996&ndash, 2017 reveals that long-term changes in UV are mainly driven by changes in aerosols, cloudiness, and surface albedo, while changes in total ozone play a less significant role. The variability of UV irradiance is large throughout Italy due to the complex topography and large latitudinal extension of the country. Analysis of the spectral UV records of the urban site of Rome, and the alpine site of Aosta reveals that differences between the two sites follow the annual cycle of the differences in cloudiness and surface albedo. Comparisons between the noon UV index measured at the ground at the same stations and the corresponding estimates from the Deutscher Wetterdienst (DWD) forecast model and the ozone monitoring instrument (OMI)/Aura observations reveal differences of up to 6 units between individual measurements, which are likely due to the different spatial resolution of the different datasets, and average differences of 0.5&ndash, 1 unit, possibly related to the use of climatological surface albedo and aerosol optical properties in the retrieval algorithms.

The goal of this study is the assessment of the reliability of the V7 TRMM (Tropical Rainfall Measuring Mission) 3B43 gridded precipitation estimates over Greece. The validation was carried out using gridded monthly precipitation data derived from 96 meteorological stations over the wider region of Greece. The TRMM 3B43 gridded estimates are on a calendar month temporal resolution and 0.25° × 0.25° spatial resolution concerning the 11-year period 1998–2008. In order to compare directly the TRMM 3B43 products with the rain gauge data, the latter were interpolated at the same spatial resolution grid with that of TRMM 3B43 (0.25° × 0.25°) and a new Greek gridded precipitation database (GGPDB) was constructed, using Kriging spatial interpolation method, taking into account the altitude of the meteorological stations. Further, to ensure reliable ground truth, we performed the comparison using data only over the 0.25° grid box when/where at least one reporting gauge is available. The annual and seasonal spatial distribution of the differences between the two datasets along with the spatial distribution of the correlation coefficients are presented and analyzed. The findings of the analysis revealed that the correlations between the two examined gridded databases (satellite and ground based) in winter were very high (r > 0.90) for the entire Greek domain with small exceptions over sparse data continental mountainous regions and restricted areas over north and south Aegean Sea. Regarding the other seasons, small correlations occur in the northern high altitude areas (Olympus Mt.) and the central/south mountainous Peloponnese. Besides, it is worth noting the remarkable small correlations over the eastern Aegean Sea and the Cyclades complex, in summer and the Cyclades complex in autumn. The TRMM 3B43 gridded data overestimate the precipitation over the Aegean and Ionian Sea, the coastal areas of Asia Minor and western Greece, in winter (> 50 mm), spring (> 25 mm) and autumn (> 60 mm). On the contrary, underestimation is demonstrated on central continental highlands (Pindus mountain range) and central mountainous Peloponnese in winter (> 150 mm), spring (25–100 mm) and autumn (60–90 mm). Summer is generally characterized by small irregularities. Generally, the findings of the performed validation indicate an underestimation at higher precipitation appeared over high altitude areas against some overestimation at lower precipitation over plains and coastal regions. The TRMM 3B43 products performance was assessed by using three contingency statistics for probability of detection (POD), false alarm ratio (FAR) and critical success index (CSI). TRMM 3B43 has POD > 80% and CSI > 60% when the monthly precipitation is lower than 84.0 mm. Moreover, the smallest POD of 44% and CSI of 34% appear when the monthly precipitation is greater than 191.5 mm. This result implies that satellite products have poor performance in estimating high monthly precipitation totals, over the Greek region.

Cloud-to-ground (CG) lightning activity recorded by the Hellenic National Meteorological Service (HNMS) Precision Lightning Network (PLN) is analysed over the wider area of Greece. In addition, the spatial and temporal relationships between TRMM 3B42 (Tropical Rainfall Measuring Mission) datasets and lightning are presented. The analyses concern the period from January 14, 2008 to December 31, 2012. The Laboratory of Climatology and Atmospheric Environment, University of Athens, has established a detailed dataset of lightning impacts over Greece from 1895 to 2013, based on digitized archive editions of newspapers. The mean seasonal variability of CG lightning activity revealed autumn as the most dominant season with 303 LD, while the mean monthly variability of CG indicated October as the most lightning active month and May as the month with a mean of 27 LD. The mean annual spatial distribution of CG lightning per km 2 , depicted the maximum frequency over Pindus mountain range (> 7 CG/km 2 ). During the autumn season, the northern Ionian Sea experienced a mean frequency of more than 5 CG/km 2 , compared to the southern Ionian Sea and NW Peloponnesus, where values of more than 7 CG/km 2 are depicted. During the summer season, the maximum frequency appeared along Pindus mountain range, around Attica, Thessaly and central Macedonia highlands. The spatial distribution of seasonal correlations between the number of CG flashes/day and gridded (TRMM 3B42) daily rainfall totals for the period 2008–2012 over Greece, indicated that correlations were mainly positive all over the under study area, within all seasons, and especially during summer and autumn. Regarding the lightning impacts in Greece, based on the 1895–2013 study period, more than 343 fatalities and at least 224 injured people have been recorded. The spatial analysis of lightning impacts, showed that the majority of events has been recorded over Greek mainland and only few scattered events have been reported over Ionian and Aegean Seas. The results of the performed research for Greece, during 1895–2013 (2000–2013), indicated that fatalities/injuries caused by lightning, were estimated at 2.9 (2) deaths/1.9 (1.6) injuries per year, respectively.

Greece is included among the most vulnerable regions of Europe by climate change on account of higher temperature and reduced rainfall in areas already facing water scarcity. With respect to wetland systems, many ephemeral ones are expected to disappear and several permanent to shrink due to climate change. As regards two specific wetlands of Greece, the change in hydroperiod of Cheimaditida and Kerkini lakes due to climate change was studied. Lakes’ water balance was simulated using historical climate data and the emission scenarios Α1Β for the period 2020–2050 and Α1Β and Α2 for the period 2070–2100. Future climate scenarios, based on emission scenarios A1B and A2, were provided in the context of the study of Climate Change Impacts Study Committee. The surface area of Lake Cheimaditida will undergo a substantial decrease, initially by 20 % during the period 2020–2050 and later until 37 % during the period 2070–2100. In Lake Kerkini, the surface area will decrease, initially by 5 % during the period 2020–2050 and later until 14 % during the period 2070–2100. Climate change is anticipated to impact the hydroperiod of the two wetlands, and the sustainable water management is essential to prevent the wetland’s biodiversity loss.

The aim of this study is to analyze and quantify the future projections of heat waves in Greece. For this reason, specific climatic indices were used in the analysis concerning absolute, percentile and duration indices defined by the CCl/CLIVAR/JCOMM Expert Team (ET) on Climate Change Detection and Indices (ETCCDI). The future projections (SRES A1B) of these indices such as summer days, tropical days, maximum daily maximum air temperature, warm days, tropical nights, maximum daily minimum air temperature, warm nights and warm spell duration were carried out using six regional climate models from the ENSEMBLES project, concerning the near future 2031–2050 and the far future 2071–2100 compared to the reference period 1961–1990. The ensemble means along with the inter-model-standard deviations of the examined extreme indices for the future model projections are presented and analyzed. Further, the findings of this analysis are discussed against recent recorded heat waves during 2007, in order to understand if such events are even more extreme or common in the future climate. It is very likely, that the anomalies observed in 2007, especially for extreme indices of minimum air temperature, could be more frequent considered as typical events by the end of the 21th century.

The impact of climate change on cotton yields in seven main arable crop sites in Greece (Agrinio, Alexandroupoli, Arta, Karditsa, Mikra, Pyrgos, Yliki) was investigated. The FAO AquaCrop (v.4) water driven model was used as a crop growth simulation tool under eight climatic models (HadRM3, C4I, REMO-MPI, ETHZ, CNRM, DMI-HIRHAM, KNMI, SMHI) based on IPPC's A1B emission scenario. The mean values of the models ensemble for temperature were +1.8 °C until 2050 and +4 °C until the end of the century. The respective values for precipitation were −11% and −24%. The research was applied over three periods, 1961–1990, 2021–2050 and 2071–2100. AquaCrop was calibrated for 2006 and validated for 2005 and 2007 using the field data from the experiments carried out in Karditsa (Central Greece). Root Mean Square Error for yield and biomass was 0.17 and 0.49 t/ha, respectively, while Index of Agreement was 0.93 and 0.94. AquaCrop was run using the Growing Degree Day mode in order to account better for the temperature variations. However, it gave erratic results for some specific climatic models (SMHI, KNMI, CNRM) in some years within the period 1961–1990. A tendency towards increasing yields by the end of the century was detected for the majority of the climate models, especially in Western Greece (Arta, Agrinio, Pyrgos) and Northern Greece (Mikra, Alexandroupoli). The efficiency of the eight models for yield predictions in the seven sites was assessed by means of a discriminant function analysis. On the account of their function coefficients over the seven sites, it was found that the models DMI and C4I explained consistently a great proportion of variation among the three time periods whereas the models ETHZ, SMHI and KNMI were more efficient only in the periods 1961–1990, 2021–2050 and 2071–2099, respectively. By running the models DMI and C4I the relative impacts of climate change on seedcotton yield in the different areas were predicted and the results were discussed on the account of the corresponding changes in precipitation, temperature and crop evapotranspiration. These results will be useful for future irrigation planning in the study areas.

Δημοσίευση σε επιστημονικό περιοδικό Summarization: Air temperatures in urban areas continue to increase because of the heat island phenomenon (UHI) and the undeniable warming of the lower atmosphere during the past few decades. The observed high ambient air temperatures intensify the energy demand in cities, deteriorate urban comfort conditions, endanger the vulnerable population and amplify pollution problems especially in regions with hot climatic conditions. The present paper analyses 40 years of hourly data series from nine meteorological stations in Greece in order to understand the impact of air temperature and relative humidity trends on the energy consumption of buildings. Using a typical office building, the analysis showed that for the period in question the heating load in the Greek building sector has decreased by about 1 kWh/m2 per decade, while the cooling load increased by about 5 kWh/m2 per decade. This phenomenon has major environmental, economic and social consequences, which will be amplified in the upcoming decades in view of the expected man-made climatic changes in this geographic area. Παρουσιάστηκε στο: Energy Conversion and Management

The objective of this study is to compare and analyze satellite precipitation extremes of Tropical Rainfall Measuring Mission level 3 output (TRMM 3B42) over Mediterranean region against the respective high resolution gridded precipitation datasets (0.25 × 0.25) based on the E-OBS project, for the period 2000–2011. The Tropical Rainfall Measuring Mission (TRMM) is a joint U.S.–Japan satellite mission to monitor tropical and subtropical precipitation and to estimate its associated latent heating. The E-OBS data set (a European daily high-resolution gridded dataset of surface temperature and precipitation) was developed as part of the European Union Framework 6 ENSEMBLES project, with the aim being to use it for validation of Regional Climate Models (RCMs) and for climate change studies. The indices used in the analysis can be divided in three categories: percentile, absolute and duration indices. The percentile indices concern: very wet days (the number of days with daily precipitation amount above the 95th percentile from the examined period) and extremely wet days (the number of days with daily precipitation amount above the 99th percentile from the examined period). The absolute threshold indices concern: number of heavy precipitation days (number of days with daily precipitation amount above 10 mm), number of very heavy precipitation days (number of days with daily precipitation amount above 20 mm) and simple daily intensity index (daily precipitation amount on wet days in a period per number of wet days in the period). The duration indices concern consecutive dry days (the largest number of consecutive days with daily precipitation amount below 1 mm) and consecutive wet days (the largest number of consecutive days with daily precipitation amount above 1 mm). The spatial distribution of the differences between the two datasets along with the spatial distribution of the correlation coefficients are presented and analyzed. Results show considerable regional differences of precipitation indices over the Mediterranean Region.

The objective of this paper is to study the spatial and temporal variability of the Aridity Index (AI) in Greece, per decade, during the 50-year period (1951–2000). Besides, the projected changes in ensemble mean AI between the period 1961–1990 (reference period) and the periods 2021–2050 (near future) and 2071–2100 (far future) along with the inter-model standard deviations were presented, based on the simulation results, derived from a number of Regional Climatic Models (RCMs), within the ENSEMBLE European Project. The projection of the future climate was done under SRES A1B. The climatic data used, concern monthly precipitation totals and air temperature from 28 meteorological stations (22 stations from the Hellenic National Meteorological Service and 6 stations from neighboring countries, taken from the Monthly Climatic Data for the World). The estimation of the AI was carried out based on the potential evapotranspiration (PET) defined by Thornthwaite (1948). The data processing was done by the application of the statistical package R-project and the Geographical Information Systems (GIS). The results of the analysis showed that, within the examined period (1951–2000), a progressive shift from the “humid” class, which characterized the wider area of Greece, towards the “sub-humid” and “semi-arid” classes appeared in the eastern Crete Island, the Cyclades complex, the Evia and Attica, that is mainly the eastern Greece. The most significant change appears during the period 1991–2000. The future projections at the end of twentieth century, using ensemble mean simulations from 8 RCMs, show that drier conditions are expected to establish in regions of Greece (Attica, eastern continental Greece, Cyclades, Dodecanese, eastern Crete Island and northern Aegean). The inter-model standard deviation over these regions ranges from 0.02 to 0.05 against high values (0.09–0.15) illustrated in western mountainous continental Greece, during 2021–2050. Higher values of inter-model standard deviation appear in the 2071–2100 ranging from 0.02 to 0.10 reaching even 0.50 over mountainous regions of the country.

This study shed light on the long term air temperature changes in the troposphere over the Mediterranean. For this purpose, we utilized the radiosonde datasets for the barometric levels at 850, 700, 500, 300, 200, 150, and 100 hPa from seventeen meteorological stations within the Mediterranean, for the period 1965–2015. Besides, the gridded reanalysis products of upper air temperature for the respective barometric pressure levels from the European Centre for Medium-Range Weather Forecasts (ECMWF, ERA-Interim) and the National Center for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) were used and compared to stations’ datasets. We analyzed the trends and variability of upper air temperature on seasonal and annual basis. The impact of atmospheric circulation, by means of specific climatic indices such as Mediterranean Oscillation Index (MOI), North Sea Caspian Pattern Index (NCPI) and North Atlantic Oscillation Index (NAOI), was also examined. The results of our analysis indicate the anthropogenic forcing to climate variability, especially in lower/middle troposphere against upper troposphere over the Mediterranean.

ECMWF-Copernicus Atmospheric Monitoring Service (CAMS) interim reanalysis (CAMSiRA) provides global atmospheric composition fields at a horizontal resolution of ~80 km and 60 hybrid sigma-pressure levels from the surface up to 0.1 hPa which can be further used to serve as boundary conditions for regional air quality models over Europe and world-wide. Here we present an evaluation of near surface ozone reanalysis for the period 2003–2013 based on measurements at rural locations from the European Monitoring and Evaluation Program (EMEP) and the European Air Quality Database (AirBase). The CAMS interim reanalysis is also compared to a control run in order to assess the impact of assimilation on near surface ozone. The evaluation results are discussed in terms of the physical processes (transport and deposition) and the chemical processes (photochemical production and destruction) that control near surface ozone variability.

This research focuses on projecting the energy demand of the building sector in Greece by calculating energy consumption, using output data from regional climate models up to 2100. More specifically, Greece was subdivided into 13 climatic zones after assessing climate model data taking into account climate change estimates for the period 2010–2100. These zones allow a detailed estimation of the effects of climate change in specific regions of the country, thus creating a database which is used to model the energy demand of the building sector in each zone. Through the use of building data from Eurostat and the European Centre for Environment, a set of three building typologies was created in relation to the building envelope, which corresponds to 85% of the building stock in Greece. These typologies were later appended to each of the 13 climatic zones and a simulation for their energy demand was calculated using climatic data from 3 distinct climatic scenarios. Results show that the energy demand for heating the building sector in Greece could decrease by about 50%, while the respective energy demand for cooling could increase by as much as 248% until 2100. These effects are more evident in the Southern part of the country.

In this study, the trends and variability of annual precipitation totals and annual rain days over land within the Mediterranean region are analyzed. Long term ground-based observations concerning, on one hand, monthly precipitation totals (1900–2010) and rain days (1965–2010) from 40 meteorological stations within the Mediterranean region were obtained from the Hellenic National Meteorological Service and the World Climate Data and Monitoring Programme (WCDMP) of the World Meteorological Organization. On the other hand, high spatial resolution (0.5° × 0.5°) gridded monthly data CRU TS 3.1 were acquired from the Climatic Research Unit, University of East Anglia, for the period 1901–2009. The two datasets were compared by means of trends and variability, while the influence of the North Atlantic Oscillation (NAO) in the Mediterranean precipitation was examined. In the process, the climatic changes in the precipitation regime between the period 1961–1990 (reference period) and the period 2071–2100 (future climate) were presented using climate model simulations (RACMO2.1/KNMI). The future climate projections were based on SRES A1B. The findings of the analysis showed that statistically significant (95% confidence level) negative trends of the annual precipitation totals exist in the majority of Mediterranean regions during the period 1901–2009, with an exception of northern Africa, southern Italy and western Iberian peninsula, where slight positive trends (not statistically significant at 95% CL) appear. Concerning the annual number of rain days, a pronounced decrease of 20 %, statistically significant (95% confidence level), appears in representative meteorological stations of east Mediterranean, while the trends are insignificant for west and central Mediterranean. Additionally, NAO index was found to be anticorrelated with the precipitation totals and the number of rain days mainly in Spain, southern France, Italy and Greece. These correlations are higher within the rain season (October–March) than the entire year. Based on the results of regional climate model RACMO2.1/KNMI, precipitation is very likely to decrease almost 20% in the period 2071–2100 compared to 1961–1990, under SRES A1B.

In this study, the variability and trends of the mean annual and seasonal maximum and minimum surface air temperature in Greece are examined, using monthly data sets of 26 meteorological stations from the Hellenic National Meteorological Service (HNMS) and gridded data from the National Center for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) Reanalysis project for the period 1955–2001. NCEP–NCAR reanalysis data sets are created by assimilating climate observations from different sources, including ships, satellites, ground stations, radiosonde observations and radar. The general purpose of conducting reanalyses is to produce multi-year global state-of-the-art gridded representations of atmospheric states, generated by a constant model and a constant data-assimilation system. The trends of the mean extreme air temperatures were evaluated, using the Mann–Kendall criterion, and, in the process, factor analysis was applied to both the stations' and the NCEP–NCAR grid points ti...

The European MACC (Monitoring Atmospheric Composition and Climate) project is preparing the operational Copernicus Atmosphere Monitoring Service (CAMS), one of the services of the European Copernicus Programme on Earth observation and environmental services. MACC uses data assimilation to combine in situ and remote sensing observations with global and regional models of atmospheric reactive gases, aerosols, and greenhouse gases, and is based on the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts (ECMWF). The global component of the MACC service has a dedicated validation activity to document the quality of the atmospheric composition products. In this paper we discuss the approach to validation that has been developed over the past 3 years. Topics discussed are the validation requirements, the operational aspects, the measurement data sets used, the structure of the validation reports, the models and assimilation systems validated, the procedure to introduce new upgrades, and the scoring methods. One specific target of the MACC system concerns forecasting special events with high-pollution concentrations. Such events receive extra attention in the validation process. Finally, a summary is provided of the results from the validation of the latest set of daily global analysis and forecast products from the MACC system reported in November 2014.

The Monitoring Atmospheric Composition and Climate (MACC) project represents the European Union's Copernicus Atmosphere Monitoring Service (CAMS) (http://www.copernicus.eu/), which became fully operational during 2015. The global near-real-time MACC model production run for aerosol and reactive gases provides daily analyses and 5-day forecasts of atmospheric composition fields. It is the only assimilation system worldwide that is operational to produce global analyses and forecasts of reactive gases and aerosol fields. We have investigated the ability of the MACC analysis system to simulate tropospheric concentrations of reactive gases covering the period between 2009 and 2012. A validation was performed based on carbon monoxide (CO), nitrogen dioxide (NO2) and ozone (O3) surface observations from the Global Atmosphere Watch (GAW) network, the O3 surface observations from the European Monitoring and Evaluation Programme (EMEP) and, furthermore, NO2 tropospheric columns, as well as CO total columns, derived from satellite sensors. The MACC system proved capable of reproducing reactive gas concentrations with consistent quality; however, with a seasonally dependent bias compared to surface and satellite observations – for northern hemispheric surface O3 mixing ratios, positive biases appear during the warm seasons and negative biases during the cold parts of the year, with monthly modified normalised mean biases (MNMBs) ranging between −30 and 30 % at the surface. Model biases are likely to result from difficulties in the simulation of vertical mixing at night and deficiencies in the model's dry deposition parameterisation. Observed tropospheric columns of NO2 and CO could be reproduced correctly during the warm seasons, but are mostly underestimated by the model during the cold seasons, when anthropogenic emissions are at their highest level, especially over the US, Europe and Asia. Monthly MNMBs of the satellite data evaluation range from values between −110 and 40 % for NO2 and at most −20 % for CO, over the investigated regions. The underestimation is likely to result from a combination of errors concerning the dry deposition parameterisation and certain limitations in the current emission inventories, together with an insufficiently established seasonality in the emissions.

An eight-year long reanalysis of atmospheric composition data covering the period 2003-2010 was constructed as part of the FP7-funded Monitoring Atmospheric Composition and Climate project by assimilating satellite data into a global model and data assimilation system. This reanalysis provides fields of chemically reactive gases, namely carbon monoxide, ozone, nitrogen oxides, and formaldehyde, as well as aerosols and greenhouse gases globally at a horizontal resolution of about 80 km for both the troposphere and the stratosphere. This paper describes the assimilation system for the reactive gases and presents validation results for the reactive gas analysis fields to document the data set and to give a first indication of its quality. Tropospheric CO values from the MACC reanalysis are on average 10-20% lower than routine observations from commercial aircrafts over airports through most of the troposphere, and have larger negative biases in the boundary layer at urban sites affected by air pollution, possibly due to an underestimation of CO or precursor emissions. Stratospheric ozone fields from the MACC reanalysis agree with ozonesondes and ACE-FTS data to within ±10% in most seasons and regions. In the troposphere the reanalysis shows biases of -5% to +10% with respect to ozonesondes and aircraft data in the extratropics, but has larger negative biases in the tropics. Area-averaged total column ozone agrees with ozone fields from a multi-sensor reanalysis data set to within a few percent. NO2 fields from the reanalysis show the right seasonality over polluted urban areas of the NH and over tropical biomass burning areas, but underestimate wintertime NO2 maxima over anthropogenic pollution regions and overestimate NO2 in northern and southern Africa during the tropical biomass burning seasons. Tropospheric HCHO is well simulated in the MACC reanalysis even though no satellite data are assimilated. It shows good agreement with independent SCIAMACHY retrievals over regions dominated by biogenic emissions with some anthropogenic input, such as the eastern US and China, and also over African regions influenced by biogenic sources and biomass burning. © Author(s) 2013., SCOPUS: re.j, info:eu-repo/semantics/published

The aim of this study is to analyze and quantify the future projections of heat waves in Greece. For this reason, specific climatic indices were used in the analysis, and concern percentile and absolute indices defined by the CCl/CLIVAR/JCOMM Expert Team (ET) on Climate Change Detection and Indices (ETCCDI). The future projections (SRES A1B) of these indices were carried out using six regional climate models from the ENSEMBLES project, concerning the near future 2031–2050 and the far future 2071–2100 compared to the reference period 1961–2000. The findings of this analysis are discussed against recent recorded heat waves in order to understand if such events are even more extreme or common in the future.

The future projections of mean air temperature in Greece for the near future 2021–2050 and distant future 2071–2100 relative to the reference period 1961–1990 are studied, analyzing the simulations from 12 Regional Climate Models (RCMs) within the ENSEMBLES European project. The simulations of the future climate were carried out on annual and seasonal basis under SRES A1B. The results showed that the mean annual air temperature in Greece will present an increase of 1.5°C and 3.2°C, for the periods 2021–2050 and 2071–2100 respectively, based on the average of the 12 climatic simulations. This increase is projected to be larger during summer and smaller during winter. Additionally, the projected warming varies among the different climatic simulations concerning the continental regions of the country especially during summer.

In the present study, an estimation of the future change in precipitation within the 21st century was carried out for the 12 climatic zones of Greece. The estimation is based on the results of 12 Regional Climate Models (RCM) simulations of the ENSEMBLES Program. The precipitation is projected to decrease mildly in the near future (2021-2050) and moderately in the far future (2071-2100) by 5% and 20% respectively for the area of Greece. The decrease seems to be most prominent during spring and summer, less prominent during winter. The autumn precipitation is projected to increase mildly in the near future and to decrease mildly in the far future. The projected precipitation change in Greece is expected to result in drastic changes on the ground water balance and on several sectors of human activity and environment parameters, as well.