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During 15–21 September 2020, an intense medicane, named Ianos, formed over the warm Mediterranean Sea. Following a path of approximately 1,900 km, Medicane Ianos affected Greece resulting in four casualties and devastating damage in the western and central parts of Greece. Persistent gale force 1-min winds up to 44 m s−1 and wind gusts up to 54 m s−1 were recorded in Cephalonia Island (Ionian Sea), while record-breaking amounts of accumulated rainfall have been recorded in several Ionian islands, as well as in parts of central Greece. Analysis of the available observations showed that Ianos was the most intense medicane ever recorded in the Mediterranean. This paper aims at investigating the genesis and evolution of the medicane, based on in situ observations, satellite measurements, and model analyses. Toward that objective, Meteosat Second Generation (MSG) SEVIRI imagery, combined with lightning data permitted to follow the evolution of convective activity during the various phases of Ianos. This investigation is complemented with upper-air model analyses in order to evaluate the synoptic environment within which Ianos had formed and was sustained over 7 days. Finally, the Global Precipitation Measurement Core Observatory (GPM CO) satellite overpasses over Medicane Ianos provided invaluable information about its 3D structure, especially during its most intense phase.

Validation is critical for quantifying accuracy, errors and limitations of models’ results. This study examines the ability of ENVI-met model to simulate thermal conditions in high spatial resolution. Field measurements from 11 central sites (squares and parks) across the greater area of Athens, Greece, incorporating 15 days of campaigns in July and August were used. Air temperature, relative humidity, wind speed, grey globe temperature and total solar radiation were monitored at 1.1 m above the ground using a mobile meteorological station. In addition, Mean Radiant Temperature, Physiologically Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI) were calculated incorporating in-situ measurements. The full force method for ENVI-met initial conditions was applied, using hourly data from the nearest meteorological stations. Validation metrics including Root Mean Square Error (RMSE), Mean Absolute Error (MAE) and the index of agreement (d) were used to measure the model accuracy. The results showed that air temperature is simulated with adequate accuracy (MAE = 1.6 ⁰C and d = 0.8) while PET and UTCI also present a high percentage of agreement (MAE = 5.3 ⁰C and 3.3 ⁰C; d = 0.7 and 0.8, respectively). Overall, the study provides further confidence that the ENVI-met can be utilized as a reliable model for further research analysis.

Flood-producing rainfall events often lead to material damage to buildings, vehicles, and infrastructure with a significant cumulative economic impact. Especially in urban areas, vulnerability to floods may vary at the local level, and so are the rainfall amounts likely to trigger flood damages. Insurance claims for flood damages can accurately indicate when and where these occurred. In the frame of the YANTAS project (project code:T2EDK-01108), a detailed insurance claims dataset of one of Greece's most important private insurance companies was used, combined with the dense surface weather station data provided by the METEO unit of the National Observatory of Athens. The aim was to model flood damage occurrence and identify the triggering rainfall thresholds at the local level across the Athens Metropolitan Area. Namely, we used eight-year rainfall observations from 66 meteorological stations and insurance claims on the postal code segmentation for the analysis. Logistic regression was applied to statistically model flood damage occurrence. We further applied the ROC curves to assess the performance of the binary response models and define optimal 24-h rainfall thresholds. The method is performed at the municipal level, as municipalities are the first administration level where decision-making to address the local risks for the citizens is needed. The rainfall thresholds were further classified to estimate and map the local risk of flood damages. The applicability of the detected thresholds in early-warning systems is also discussed.

The METEO unit of the National Observatory of Athens has developed a methodology for ranking rain storms in Greece, following a similar procedure in the USA, where ranking of snow storms is routinely performed. The rain storm ranking in Greece is performed through the calculation of the Regional Precipitation Index (RPI) which takes into account:a) The daily accumulated precipitation and its exceedance of specific percentile thresholds.b) The total area where these exceedances occur. c) The population of the area that these exceedances occur.First, RPI calculations were applied in ERA5-Land rainfall re-analysis, available at 0.1 deg resolution, for a 30-year period spanning from 1991 to 2020 and all major storms that occurred within this period were ranked and correlated to the reported societal impacts. The ranking of the storms is performed based on the percentiles of all non-zero RPI in the examined period. As major storms we define the top 2% of RPI. Then, a proposed methodology for the application of the methodology on daily forecast fields provided by high-resolution numerical weather prediction models is tested and discussed. This work, was funded by the European Climate Foundation.

The METEO unit of the National Observatory of Athens has developed and applies a set of operational services that employ state-of-the-art observational and modeling techniques with the aim to assist both the citizens and the authorities in better preventing, addressing, and ultimately mitigating the adverse impacts of forest fires. The early warning system platform, which has been initially developed in the frame of DISARM project, had been upgraded with improved functionalities in the frame of the CLIMPACT project, a flagship initiative on climate change to coordinate a Pan-Hellenic network of institutions. The presentation focuses on the description of the system that encompasses the following pillars: (a) Forecasting of forest fire danger: four widely used indices (Canadian Fire Weather Index - CFWI, Modified Nesterov, Fosberg and Haines) are operationally calculated for the next 3 days at 6kmx6km and 2kmx2km spatial resolution based on 3 state-of-the-art numerical weather prediction models (WRF, Bolam, Moloch). Especially for CFWI the fire danger thresholds have been adapted to the fire environment of Greece; (b) Real time monitoring of the fire weather conditions: The monitoring is based on the online network of meteorological stations operated by the METEO Unit of NOA that includes ~450 stations across Greece. Fire weather monitoring also includes the daily estimation of landscape flammability using as a proxy the dead fuel moisture content (DFMC). DFMC is calculated using a physically based fuel moisture model and weather station data. (c) IRIS a rapid response system for fire spread forecasting: WRF-ARW NWP model and FIRE two-dimensional fire spread model are applied, along with a prototype high-resolution geospatial dataset for the representation of fuels, in a fully-coupled mode in order to account for the two-way interaction between fire and the atmosphere . Major upgrades of the IRIS system achieved in the frame of CLIMPACT include the online calculation of dead fuel moisture, the increase of spatial resolution (40mx40m pixels) of the prototype fuel model for Greece, and the delivery of a forecast guidancewhich includes the categorization (using a 7-level scale) of forest fires based on the forecasted behavioral characteristics.

In late March 2018, a large part of the Eastern Mediterranean experienced an extraordinary episode of African dust, one of the most intense in recent years, here referred to as the "Minoan Red" event. The episode mainly affected the Greek island of Crete, where the highest aerosol concentrations over the past 15 yeas were recorded, although impacts were also felt well beyond this core area. Our study fills a gap in dust research by assessing the multi-sectoral impacts of sand and dust storms and their socioeconomic implications. Specifically, we provide a multi-sectoral impact assessment of Crete during the occurrence of this exceptional African dust event. During the day of the occurrence of the maximum dust concentration in Crete, i.e. March 22nd, 2018, we identified impacts on meteorological conditions, agriculture, transport, energy, society (including closing of schools and cancellation of social events), and emergency response systems. As a result, the event led to a 3-fold increase in daily emergency responses compare to previous days associated with urban emergencies and wildfires, a 3.5-fold increase in hospital visits and admissions for Chronic Obstructive Pulmonary Disease (COPD) exacerbations and dyspnoea, a reduction of visibility causing aircraft traffic disruptions (eleven cancellations and seven delays), and a reduction of solar energy production. We estimate the cost of direct and indirect effects of the dust episode, considering the most affected socio-economic sectors (e.g. civil protection, aviation, health and solar energy production), to be between 3.4 and 3.8 million EUR for Crete. Since such desert dust transport episodes are natural, meteorology-driven and thus to a large extent unavoidable, we argue that the efficiency of actions to mitigate dust impacts depends on the accuracy of operational dust forecasting and the implementation of relevant early warning systems for social awareness., The authors gratefully acknowledge the COST Association for funding the COST Action inDust (CA16202) as well as the WMO Sand and Dust Storm Warning Advisory and Assessment System (SDS-WAS) and the ERA4CS DustClim and the AXA Research Fund for funding the AXA Chair on Sand and Dust Storms (hosted by the Barcelona Supercomputing Center). We thank the scientific team of the PROTEAS CSP facility for the feedback provided and T. Bojic and R. Burbidge for facilitating the access to the EUROCONTROL archive. We thank the scientific team of the PROTEAS CSP facility for providing DNI data for this case study. Thanks are due to FCT/MCTES for the financial support to CESAM (UIDP/50017/2020+UIDB/50017/2020) through national funds, and also to the Icelandic Research Fund for the grant no. 207057-051. Authors S. Kazadzis and P. Kosmopoulos would like to acknowledge the European Commission project EuroGEO e-shape (grant agreement No 820852). Also, International Cooperative for Aerosol Prediction (ICAP) and NASA mission researchers are gratefully for providing aerosol data for this study. Aurelio Tobias was supported by MCIN/AEI/10.13039/501100011033 (grant CEX2018-000794-S). S. Kutuzov acknowledges the Megagrant project (agreement No. 075-15-2021-599, 8.06.2021).

On 23 July 2018, Attica, Greece, was impacted by a major wildfire that took place in a wildland–urban interface area and exhibited extreme fire behavior, characterized by a very high rate of spread. One-hundred civilian fatalities were registered, establishing this wildfire as the second-deadliest weather-related natural disaster in Greece, following the heat wave of July 1987. On the day of the deadly wildfire, a very strong westerly flow was blowing for more than 10 h over Attica. Wind gusts up to 30–34 m s−1occurred over the mountainous areas of Attica, with 20–25 m s−1in the city of Athens and surrounding suburban areas. This strong westerly flow interacted with the local topography and acted as downslope flow over the eastern part of Attica, with temperatures rising up to 39°C and relative humidity dropping to 19% prior to the onset of the wildfire. These weather elements are widely acknowledged as the major contributing factors to extreme fire behavior. WRF-SFIRE correctly predicted the spatiotemporal distribution of the fire spread and demonstrated its utility for fire spread warning purposes.

On 1st and 2nd February 2015, the central and eastern Mediterranean, as well as parts of the Black Sea, were affected by an extreme desert dust outbreak. This exceptional dust event took place under the prevalence of a strong southwesterly airflow over the region, with maximum wind speeds up to 70 (36 ms−1) and 35 knots (18 ms−1) at 700 hPa and at mean sea-level pressure, respectively. Based on MODIS-Terra/Aqua aerosol optical depth (AOD) retrievals, the intensity of the transported dust loads maximized over the central Mediterranean (4.2) while very high AODs (up to 2.5) were recorded over Greece and the Black Sea. In addition, according to in-situ measurements obtained at Finokalia (Crete, southern Greece), the maximum PM10 concentrations reached up to 758 μgr m−3 (maximum levels for 2015). Through the implementation of the WRF-Chem model, the clear-sky direct radiative effects (DREs) have been computed for the SW, LW and NET (SW + LW) radiation, at the top of the atmosphere (TOA), within the atmosphere (ATM) as well as for the downwelling (SURF) and the absorbed (NETSURF) radiation at the ground. According to our simulations, during daytime, the instantaneous NET DREs reach down to −278.1 Wm−2 (Solar Zenith Angle (SZA) = 53°) and − 252.2 Wm−2 for SURF and NETSURF, respectively, indicating a strong surface cooling, while the corresponding values for ATM can be as large as 147.3 Wm−2 (SZA = 50°) revealing a strong atmospheric warming. At TOA, the computed DREs vary from −120.1 Wm−2 (planetary cooling; SZA = 51°) to 59.4 Wm−2 (planetary warming; SZA = 64°) being negative and positive over dark and bright surfaces, respectively. During nighttime, reverse effects of lower magnitude are found at all levels of the Earth-Atmosphere system. At a regional scale, throughout the forecast period, the clear-sky NET DREs range from −16.60 Wm−2 to −0.76 Wm−2, from −46.18 Wm−2 to 16.11 Wm−2, from −32.31 Wm−2 to 13.70 Wm−2 and from −14.63 Wm−2 to 20.40 Wm−2 for TOA, SURF, NETSURF and ATM, respectively. As a response to the perturbation of the surface radiation budget, the 2 m air temperature decreases/increases by up to 1.5 °C (5.3 °C) during daytime/nighttime. Moreover, at noon, the low-level dust layer (up to 3 km above sea level), cools (heats) the lowest troposphere by up to 0.5 °C (1.4 °C) over land (sea). At night, the temperature of the atmospheric layers where the dust aerosols are confined decreases (by up to −1.8 °C), whereas a warming effect (by up to 2.8 °C) is evident in the air masses beneath the dust layer. Through the inclusion of dust-radiation interactions in the numerical simulations, the model's predictive skill in terms of reproducing the downwelling SW radiation at the ground is improved. This is justified via the comparison of the RADON (dust-radiation interactions are activated) and RADOFF (dust-radiation interactions are deactivated) outputs against cloud-free observations derived by 31 NOAAN stations. More specifically, from RADOFF to RADON, the bias reduces from 157.63 to 26.02 Wm−2 and the slope decreases from 1.25 to 0.98. On the contrary, the evaluation analysis of the temperature at 2 m does not reveal a remarkably better performance of the RADON run, particularly during sunlight hours, reflecting thus the predominance of first order model errors over the expected improvements attributed to dust-radiation interactions.

This study examines the mechanisms of flood-risk precautionary behavior among Greek citizens. To that end, we specify and test a mediation model in which awareness-raising factors and confidence attitudes influence the citizens' current flood preparedness and preparedness intention through perceptual and emotional processes. Raw data were obtained via an online survey that received 1855 responses. Causal relations were tested by means of structural equation modeling (SEM). Overall, results indicate that risk perception and worry are significant drivers of preparedness intention. In particular, they act as mediating variables, explaining how flood experience, access to more risk information, vulnerability awareness, and trust in authorities affect citizens' intention to invest in precautionary measures. Especially trust was found to have a negative effect on worry, leading to lower preparedness levels. Worry was also found to have a significant role in explaining the current preparedness levels. Interestingly, citizens who had already undertaken precautionary measures in the past appear to be more willing to invest in more measures. Implications for improving flood-risk management in Greece are discussed.

Laymen’s awareness for the natural hazards and their perception of the associated risks at the local level have been acknowledged widely as key factor for the success of any risk mitigation initiative. It is therefore particularly beneficial to find out how people's risk perception is shaped in a multi-hazard environment, such as that of Eastern Mediterranean, and how it affects individual preparedness. To this end, we have conducted an online survey aimed at Greek citizens in order to better understand their risk perception among various hydro-meteorological hazards, including geophysical hazards for comparison, and to evaluate their coping capacity. The survey questionnaire received more than 2,300 responses from across Greece. The analysis of the questionnaire has been performed in the frame of the project “THESPIAN II – Development of synergistic and integrated methods and tools for monitoring, management and forecasting of Environmental parameters and pressures”.Statistical results show that people consider hydro-meteorological hazards less worrying and dangerous than earthquakes. However, in contrast to earthquakes, it was found that increase in hydro-meteorological risks perception enhances preparedness i.e. the adoption of adequate protective measures, except of the private insurance coverage which was found to be purely a matter of economic criteria. Experience was found to have a significant impact on both risk perception and preparedness for all types of natural hazards. However, with respect to hydro-meteorological hazards, its effect decreases with time. Results also highlight the important role of a focused and coordinated effort by authorities and scientists to inform citizens and build a trustful relationship in motivating individual preparedness, as well as other interesting statistically significant relationships with participants demographics and other factors.

The spatio-temporal regime of lightning strokes over the broader Greek area is studied using 15-day ZEUS cloud-to-ground lightning data for a 10-year period (2005–14). The multivariate statistical method Factor Analysis (S-mode and T-mode) is applied on the mean intra-annual variation of lightning in order to reveal: i) the main modes of intra-annual variation of lighting activity that correspond to specific sub-regions of the Greek area and ii) the main characteristic patterns of strokes prevailing during specific periods of the year (“seasons”). According to the results there are three main modes of intra-annual variation: a) the continental one with maximum lightning activity in early summer, b) the Ionian Sea one with maximum in early autumn and c) the Aegean Sea one with maxima in middle autumn and late May. Also, according to the patterns of strokes, three main “seasons” are found: a) the summer one (early May–middle August) with highest lightning activity over the continental regions of the country due to the atmospheric instability associated with the intense land heating and the persistence of cool upper air masses, b) the winter one (middle December–middle February) with the maximum of lightning activity over the sea where instability is high due to the frequent prevalence of cold air masses over the warm sea-surface and the associated passages of Mediterranean depressions and c) the autumn one (early September–middle October) with maximum over northwestern Greece associated with the early cold season low pressure systems, the warm sea body of Ionian Sea and the essential role of topography.

Mediterranean thunderstorms climatology is analyzed for a 10-year period from 2005 to 2014. For this analysis, we applied a clustering method to the cloud-to-ground lightning stroke dataset, derived from the ZEUS detection system, operated by the National Observatory of Athens. Results showed that the annual days of thunderstorm occurrence are dependent on the diurnal cycle of insolation and on the underlying topographic features. Therefore, the majority of thunderstorms occur over land in spring and summer, while winter and autumn thunderstorms tend to occur over the sea. On average, winter thunderstorms are less frequent and of lower intensity than the ones of summer, but last longer, tend to attain larger sizes and are associated with significantly higher velocity. Regardless the season, all thunderstorms tend to propagate towards the east, while their speed is higher in winter and autumn. In particular, for thunderstorms occurring over land, we found that the higher the duration of the lifetime of a thunderstorm, the earlier in the day it is expected to occur. Mediterranean thunderstorms size and duration have been found to be correlated, while a linear relation was determined between thunderstorms intensity and rainfall over the Mediterranean region, where the rain yield was estimated to be about 1.8 108 kg of rainfall per CG lightning.

An intense and fast moving convective line that crossed Massif Central/Cevennes-Vivarais area (south France) during the field campaign of Hydrological Cycle in Mediterranean Experiment (HyMeX) — Special Observing Period 1 (SOP1) is examined. The mesoscale analysis demonstrates a complex convective system with a V-shape in the Infrared (IR) satellite imagery and a squall line pattern on the radar imagery. Ground stations observed up to 60 mm h− 1 of rain accumulation, while the lightning activity, as observed by 4 detection networks, was also exceptionally high. The Weather Research and Forecasting (WRF) model was used to simulate this convective episode and sensitivity tests were performed with various microphysics and convective parameterization schemes. Satellite data from Meteosat SEVIRI Rapid Scanning Service were used in conjunction with radar, lightning and rain gauge data to conclude on the best simulation for which WRF model exhibits a rather precise and realistic distribution and evolution of the precipitation patterns. Finally, a study of the microphysics was performed indicating the interconnection of graupel with lightning activity, confirming recent results, compared against a sophisticated hydrometeor classification radar algorithm and lightning data.

The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite has been utilized for the first time in a study regarding lightning activity modulation due to aerosols. Lightning activity observations, obtained by the ZEUS long range Lightning Detection Network, European Centre for Medium range Weather Forecasts (ECMWF) Convective Available Potential Energy (CAPE) data and Cloud Fraction (CF) retrieved by MODIS on board Aqua satellite have been combined with CALIPSO CALIOP data over the Mediterranean basin and for the period March to November, from 2007 to 2014. The results indicate that lightning activity is enhanced during days characterized by higher Aerosol Optical Depth (AOD) values, compared to days with no lightning. This study contributes to existing studies on the link between lightning activity and aerosols, which have been based just on columnar AOD satellite retrievals, by performing a deeper analysis into the effect of aerosol profiles and aerosol types. Correlation coefficients of R = 0.73 between the CALIPSO AOD and the number of lightning strikes detected by ZEUS and of R = 0.93 between ECMWF CAPE and lightning activity are obtained. The analysis of extinction coefficient values at 532 nm indicates that at an altitudinal range exists, between 1.1 km and 2.9 km, where the values for extinction coefficient of lightning-active and non-lightning-active cases are statistically significantly different. Finally, based on the CALIPSO aerosol subtype classification, we have investigated the aerosol conditions of lightning-active and non-lightning-active cases. According to the results polluted dust aerosols are more frequently observed during non-lightning-active days, while dust and smoke aerosols are more abundant in the atmosphere during the lightning-active days.

The FLIRE DSS is a web-based Decision Support System for the combined forest and flood risk management and planning. State of the art tools and models have been used in order to enable Civil Protection agencies and local stakeholders to take advantage of web based DSS with no need of local complex infrastructure and maintenance. Civil protection agencies can predict the behavior of a fire event using real time data and in that way to plan its efficient elimination. Also, they can implement what-if scenarios for areas prone to fire and thus develop plans for forest fire management. Flood services include flood maps and flood-related warnings; these become available to relevant authorities for visualization and further analysis on a daily basis. Real time weather data from ground stations provide the necessary inputs for the calculation of the fire model in real time and a high resolution weather forecast grid support flood modeling and what-if scenarios for the fire modeling. The innovations of the FLIRE DSS are the use of common Earth Observation (EO) data as the backbone of the system to produce data for the support of fire and flood models, the common use of weather related information, the distributed architecture of the system and the web-based access of it with no need for installation of dedicated software. All these can be accessed by all means of computer sources like PC, laptop, Smartphone and tablet either by normal network connection or by using 3G and 4G cellular network. The latter is important for the accessibility of the FLIRE DSS during firefighting or rescue operations during flood events. FLIRE DSS can be easily transferred to other areas with similar characteristics due to its robust architecture and its flexibility. Display Omitted The FLIRE DSS, a web-based Decision Support System, provides a web platform for the management of fire and flood cases in urban and periurban areas.Collect once - use for many rule is applied for the input data which are used for the fire and flood models.What-if scenarios can be applied for the case of fire and flood for an efficient planning during the high risk periods.The innovation aspects of the system is the use of hypertemporal Earth Observation data for fire and flood model support.

Climate-related hazards, such as wildfires and hydrogeological phenomena, cause extensive damages and casualties around the world. Despite the recent advances and technologies for risk mitigation, it is acknowledged that public risk perception is a critical factor for these tools to succeed. Greece and the broader Eastern Mediterranean is an area where, despite the diversity of natural disasters, there is a lack of understanding of the hazard types that people are most concerned with and how they measure against other groups of hazards (i.e., geophysical). This work uses an online survey targeting Greek people, aiming to provide a better understanding of their perception of different natural hazards. Statistical results show that people consider climate-related hazards less dangerous and likely to occur than earthquakes, which occur often as zero-impact events. Laymen may thus underestimate certain risks, which may inhibit appropriate preparation. Disaster experience was found to increase threat perceptions and to motivate preparedness. However, in what concerns climate-related hazards, the effect of experience may fade out over time. Awareness activities were found to associate with higher emergency response efficacy. Males exhibit lower risk perception and higher coping appraisals. However, prioritization of risks is almost identical between genders. Implications for risk management are discussed.

Floods are one of the most lethal natural hazards. Recent studies show that in a large percentage of flood-related fatalities, victims engage in risk-taking behavior by getting deliberately in contact with floodwaters. This study integrates behavioral psychology and situational environmental factors with the aim to examine why individuals undertake such risky behavior. In particular, we draw on the theory of planned behavior (TPB) to link water depth perception with the intention of car drivers to enter floodwaters. The hypotheses on which the study was based were that the depth of the water adversely affects the driver’s intention to enter floodwaters, and that this effect is mediated by a behavior-favorable attitude, a behavior-favorable subjective norm, and perceived behavioral control. Further, to understand the conditions under which this process works, the moderating role of past behavior in the above relationships is also examined. Results from an experimental study (n = 1940) show that water depth perception affects intention. Attitude, perceived behavioral control, and normative beliefs operate as the underlying psychological mechanism that leads to the mitigation of intention in higher water depth situations. Interestingly, past risk-taking behavior is found to be a significant condition under which this process works, by mostly affecting individuals’ attitudes. Mediation and moderated mediation analyses were conducted to estimate causal relationships. The findings provide evidence of the significant interaction that environmental, psychological, and precedent behavioral factors have on behavioral intentions.

This study presents the evaluation of 1 year of operational lightning forecasts provided for Europe, using the Weather Research and Forecasting model coupled with a cloud-top height-based lightning parameterization scheme. Three different convective parameterization schemes were employed for parameterizing sub-grid cloud-top heights and consequently driving the lightning scheme. Triggering of the lightning scheme was controlled by means of a model-resolved microphysics-based masking filter, while the formulation for deriving lightning flash rates was also modified, assuming a single “marine” equation instead of the original equations discriminating between continental and marine lightning. Gridded lightning observations were used for evaluating model performance on a dichotomous decision basis. Analysis showed that the lightning scheme is sensitive to the parameterization of convection. In particular, the Kain–Fritsch convective scheme was found to outperform the Grell–Devenyi and Grell–Freitas schemes, showing a statistically significant better performance with respect to lightning prediction. This was most evident during the warm season, while smaller differences among the schemes were recorded during the cold season. Further, for all examined convective schemes, it was found that the application of the masking filter is desirable for improving model performance in terms of lightning forecasting. Last, the reported results revealed that the refinement of the formulation of the lightning parameterization scheme, adhering to a “global” marine equation instead of distinguishing between land and sea lightning, may be necessary in order to obtain reliable lightning forecasts.

The Axios Valley, located in central-northern Greece, is surrounded by complex topography that plays a significant role in the modification of wind flow, both in terms of speed and direction. The characteristic wind regime of this valley is Vardaris, a northwesterly wind that prevails in this region, especially during the cold period of the year. Vardaris is well known for its consistent direction and high intensity, as well as for the effective advection of cold and dry air, often resulting to significant damages in local infrastructures and agriculture. A field campaign under the name AXIOS took place during the period from November 2007 through May 2008 in order to examine this particular wind flow. The analysis of the in situ observational data, which was funded by the research program THESPIA-KRIPIS, showed that topography plays a key role in intensifying Vardaris, generating gusts that approximated 30 m s− 1 during the experimental period. The air temperature and humidity fields were also found to be significantly influenced. In addition to the observational study, an intense Vardaris episode was simulated with the Weather Research and Forecasting (WRF) model at high horizontal resolution. Results revealed that the model was able to reproduce the favorable environmental conditions that lead to Vardaris occurrence, providing a useful insight on the physical mechanisms explaining its structure.

In the framework of this study, the effect of aerosols on lightning activity has been investigated for the first time over the broader Mediterranean Sea. Atmospheric optical depth data retrieved by MODIS on board Aqua satellite and cloud to ground lightning activity data provided by ZEUS network operated by the National Observatory of Athens were analyzed for a time period spanning from 01/01/2005 up to 31/12/2013. The results indicate the importance of aerosols in lightning modulation. The mean aerosol optical depth (AOD) values of the days with lightning activity were found to be higher than the mean seasonal AOD in 90% of the under study domain. Furthermore, the increasing rate of lightning activity with increasing aerosol loading was found to be more pronounced during summertime and for AOD values up to 0.4. Additionally, the spatial analysis showed that the percentage of days with lightning activity during summertime is increasing with increasing AOD. Finally, time series showed similar temporal behavior between AOD seasonal anomalies and days with lightning activity differences. Both the spatial and temporal analysis showed that lightning activity is correlated to AOD, a characteristic consistent for all seasons.

A web-based Decision Support System, named FLIRE DSS, for combined forest fire control and planning as well as flood risk management, has been developed and is presented in this paper. State of the art tools and models have been used in order to enable Civil Protection agencies and local stakeholders to take advantage of the web based DSS without the need of local installation of complex software and their maintenance. Civil protection agencies can predict the behavior of a fire event using real time data and in such a way plan its efficient elimination. Also, during dry periods, agencies can implement “what-if” scenarios for areas that are prone to fire and thus have available plans for forest fire management in case such scenarios occur. Flood services include flood maps and flood-related warnings and become available to relevant authorities for visualization and further analysis on a daily basis. When flood warnings are issued, relevant authorities may proceed to efficient evacuation planning for the areas that are likely to flood and thus save human lives. Real-time weather data from ground stations provide the necessary inputs for the calculation of the fire model in real-time, and a high resolution weather forecast grid supports flood modeling as well as the development of “what-if” scenarios for the fire modeling. All these can be accessed by various computer sources including PC, laptop, Smartphone and tablet either by normal network connection or by using 3G and 4G cellular network. The latter is important for the accessibility of the FLIRE DSS during firefighting or rescue operations during flood events. All these methods and tools provide the end users with the necessary information to design an operational plan for the elimination of the fire events and the efficient management of the flood events in almost real time. Concluding, the FLIRE DSS can be easily transferred to other areas with similar characteristics due to its robust architecture and its flexibility.

Lightning activity is analysed in a sector covering the Eastern Mediterranean (16–32°E, 34–46°N) for the years 2005–2014. The study is based on the use of cloud-to-ground (CG) lightning activity data retrieved from ZEUS system, operated by the National Observatory of Athens, and examines the seasonal, diurnal and spatial variability of the lightning activity. The effect of elevation, terrain slope, vegetation cover and convective available potential energy (CAPE) on the distribution of the CG lightning strokes is also investigated. Lightning is modulated by the diurnal cycle of insolation and the underlying topographic features of the region. The lightning strokes are more numerous over the mainland than over the sea. CG lightning activity is dominant over the land and the coastal areas during spring and summer while during the coldest period of the year it is dominant over the sea. The maximum value of lightning activity is observed in June and mostly in the afternoon. The orography and the terrain slope affect the distribution of lightning. During the warmest period of the year, the forested areas have an increased “lightning yield”. The number of CG lightning strokes increases with increasing CAPE and the high correlation between them indicates that CAPE values could be used as a proxy for the presence of lightning activity, at least over the eastern Mediterranean region.

The objective of the following paper is to identify weather-related thresholds for wildfire danger, i.e., the potential extent of fire, based on local weather conditions. The target area is Greece, a wildfire prone Mediterranean country which experienced on average 2000 wildfires annually over the last two decades. Initially, the Fire Weather Index (FWI) component of the Canadian Fire Weather Index (FWI) System (FWI System) adopted by the European Forest Fire Information System (EFFIS), is evaluated with respect to its wildfire danger predictive ability. Hence, weather and wildfire data at municipality level and on a daily basis, for the period 2000–2016 are exploited. The analysis showed that the FWI thresholds proposed by EFFIS for assessing the level of fire danger in Europe are too low for the case of Greece and, therefore, are not representative of the country's fire weather conditions. Two statistical approaches, cluster analysis and non-linear least-squares regression, are subsequently applied to determine the most appropriate FWI thresholds for discrete levels of wildfire danger. The results are presented in 4 sets of FWI thresholds and they are further evaluated on the basis of verification measures. All sets of FWI thresholds were found to significantly improve the predictability of wildfire danger compared to the EFFIS fire danger class thresholds. In particular, two of them were found to meet selected performance requirements for a balanced predictive performance, namely a reduced overestimation of wildfire danger and increased reliability in danger classification. The results are expected to have significant practical implications for wildfire prevention and risk mitigation strategies implemented by the forest fire control agencies of the country.

The purpose of this study is the verification of the BOLAM weather prediction model over the area of Cyprus. The verification period spans from 1 January 2007 till 31 December 2007 and the parameters studied are: temperature, wind and precipitation. The model forecasts are compared to the observations recorded at three locations on the island, where Automatic Weather Observing Systems are operated by the Meteorological Service of Cyprus, namely, those of Larnaka and Paphos Airports and at Athalassa. The statistical analysis includes calculation of the mean error, the mean absolute error and the standard deviation. Based on the construction of a contingency table, the probability of detection of a precipitation event and the false alarm rate are calculated. Finally, an example of BOLAM forecasts for a case study of a low pressure affecting Cyprus during winter is presented and discussed.

This paper presents first results on the investigation of the synoptic conditions that led to the rapid development of a low-pressure system over the Aegean Sea. Indeed, during the period 21–22 January 2004, a very deep cyclone was observed over the Aegean Sea with a minimum central pressure of ~972 hPa, a value which is among the lowest observed over the entire Mediterranean Sea during the last 40 years. The rapid development was associated with a two-trough system that, under the influence of a very intense upper-level jet, was merged in one and then acquired a negative tilting. Additional information on the mesoscale organisation of the system is given, based on lightning data and space borne microwave and infrared observations.

This paper presents the development of an operational forecasting service focusing on human-biometeorological conditions. The service is based on the coupling of numerical weather prediction models with an advanced human-biometeorological model. Human thermal perception and stress forecasts are issued on a daily basis for Greece, in both point and gridded format. A user-friendly presentation approach is adopted for communicating the forecasts to the public via the worldwide web. The development of the presented service highlights the feasibility of replacing standard meteorological parameters and/or indices used in operational weather forecasting activities for assessing the thermal environment. This is of particular significance for providing effective, human-biometeorology-oriented, warnings for both heat waves and cold outbreaks.

In this work the impact of topography on the distribution and the amount of precipitation in Epirus, NW Greece is investigated, during the cold period of the year. A precipitation event with typical wintertime characteristics is considered. In the selected case, extended and heavy precipitation over Epirus is caused by a low pressure system centred northwest of Epirus and moving southeastwards, generating southerly winds over the Ionian Sea. The case is simulated by applying the numerical meteorological model MM5 in a high resolution grid (2 × 2km). Various sensitivity tests are performed, searching for the model initialization time and the convective parameterization scheme (CPS) leading to the best simulation of the observed event. Then, the model is applied again incorporating modified data of topography, in order to study the differentiations in the fields of the most important meteorological parameters, which are directly related with precipitation. The topography is modified with two ways: either by reducing the height of the mountains (type RT) or by elevating the terrain height (type ET). The results show that in the RT type, the precipitation field appears more homogeneous, with weaker maxima on the windward sides and above the mountain ridges. As a consequence, less rain falls in these areas and humid air passes easier to the lee sides reducing rain shadows. In the ET type, rain increases in the windward coastal zone of Epirus while it is reduced in the inland areas where less humid air is available. Generally, the modification of topography changes the flows near the surface, causing a displacement of the convergence zones and thus a new distribution of vertical velocities, which, combined with the new water vapour field, has a direct impact on precipitation.

Over the past several decades, flash floods that occurred in Attica, Greece, caused serious property and infrastructure damages, disruptions in economic and social activities, and human fatalities. This paper investigated the link between rainfall and flash flood impact during the catastrophic event that affected Attica on 22 October 2015, while also addressing human risk perception and behavior as a response to flash floods. The methodology included the analysis of the space–time correlation of rainfall with the citizens’ calls to the emergency fire services for help, and the statistical analysis of people’s responses to an online behavioral survey. The results designated critical rainfall thresholds associated with flash flood impact in the four most affected subareas of the Attica region. The impact magnitude was found to be associated with the localized accumulated rainfall. Vulnerability factors, namely, population density, geographical, and environmental features, may have contributed to the differences in the impact magnitudes between the examined subareas. The analysis of the survey’s behavioral responses provided insights into peoples’ risk perception and coping responses relative to the space–time distribution of rainfall. The findings of this study were in agreement with the hypothesis that the more severe the rainfall, the higher peoples’ severity assessment and the intensity of emotional response. Deeper feelings of fear and worry were found to be related to more adjustments to the scheduled activities and travels. Additionally, being alert to the upcoming rainfall risk was found to be related to decreased worry and fear and to fewer changes in scheduled activities.

The increasing maritime activity can be seriously affected by severe weather and sea conditions. To avoid serious damages to ships, marine structures and humans, a good weather and wave forecast is of primary importance. In general the meteorological and the wave models are used to produce forecasts at large scale like the global or the medium-size inner seas. For much smaller environments like the Greek maritime areas, characterized by complicated features like the orography and the presence of islands, the modelisation becomes a not simple task. This study is devoted to the validation of the performance of the WAM wave model over the Ionian and Aegean Seas. The period of validation refers to the first 12 months of operational use of the model at the National Observatory of Athens. The wave model is applied at a resolution of 1/16 degrees and is driven by the 10 m wind, produced by the BOLAM meteorological model operationally run over the same area. Two different sources of data have been used for the verification of the model results. The first dataset is provided by a network of buoys deployed over the Greek maritime areas and the second consists of altimeter data, provided by the OSTM/Jason-2 satellite platform. Although the study area is characterized by complex topography and a large number of islands, the implementation of the WAM model provides very encouraging results. In general, with the exception of the two buoys located in the Ionian Sea, the WAM model tends to underestimate the wave energy in the region of the Aegean Sea. The comparison with the altimeter data shows that the model has a tendency to overestimate the height for waves lower than 2.5 m and to underestimate the waves higher than 3 m.

Flash floods that occurred in the urban part of Attica, Greece, in the last decades, have caused, overall, serious property and infrastructure damages, economic and social activities impediment and, occasionally, human fatalities. This paper investigates the relationship between the rainfall hazard and the induced impact, as measured by impact indicators, and examines the effect of the social factor on the vulnerability of the system exposed to the flash flood risk. The study focuses on the catastrophic flash flood event that affected Attica on October 22, 2015. The methodology includes the analysis of the spatiotemporal distribution of rainfall and citizens’ calls to the Fire Service emergency for help during the event, as well as the analysis of people’s responses at an on-line behavioral survey. Results feature the roles of the rainfall hazard and of the society on the flash flood impact and contribute to a more integrated view of the flash flood risk in an urbanized environment.

The intra-annual variation and the spatial distribution of lightning activity over Greece is studied for the 10-year period 2005–14, on a 15-day basis, using Zeus 0.5° × 0.5° data. Factor Analysis (S-mode and T-mode) is applied to the average lightning activity for each fortnight of the year and for each grid box, for the studied period. (i) For the intra-annual variation of lightning activity, 3 sub-regions are defined, presenting characteristic modes of variation: In the first one, over the mainland, a broad maximum appears during late spring–early summer; in the second, mainly over the Ionian Sea, a maximum is seen during early autumn; while in the third, mainly over the central and south Aegean Sea, two maxima are found, one in middle autumn and another in late May. (ii) For the spatial distribution of lightning activity, 4 main patterns are revealed: the ‘summer’ pattern (1/5–15/8), characterized by a maximum over the mainland; the ‘autumn’ pattern (1/9–15/10), with maxima over the north Ionian Sea and the north Aegean Sea; the ‘winter’ pattern (15/12–15/2), with maxima over the south Ionian Sea and Dodecanese Islands; and a low variance ‘transitional’ pattern (1/4–30/4 and 1/12–15/12), with maximum over the central Aegean Sea.

An intense and fast moving convective line that crossed Massif Central/Cevennes—Vivarais area (south France) during the field campaign of HYdrological cycle in Mediterranean EXperiment (HyMeX)—Special Observing Period 1 (SOP1) is examined. The mesoscale analysis demonstrates a complex convective system with a V-shape in the Infrared (IR) satellite imagery, while ground stations observed up to 100 mm of rain accumulation. The Weather Research and Forecasting (WRF) non-hydrostatic model was used to simulate this convective episode and sensitivity tests were performed on explicit microphysics, as well as on convective parameterizations in high resolution domains. Satellite data from SEVIRI Rapid Scan Service were used in conjunction with rain gauge data to conclude at the best simulation at which the WRF model exhibits a rather precise and realistic distribution and evolution of the precipitation patterns.

One of the costliest natural hazards around the globe is flash floods, resulting from localized intense convective precipitation over short periods of time. Since intense convective rainfall (especially over the continents) is well correlated with lightning activity in these storms, a European Union FP6 FLASH project was realized from 2006 to 2010, focusing on using lightning observations to better understand and predict convective storms that result in flash floods. As part of the project, 23 case studies of flash floods in the Mediterranean region were examined. For the analysis of these storms, lightning data were used together with rainfall estimates in order to understand the storms' development and electrification processes. In addition, these case studies were simulated using mesoscale meteorological models to better understand the local and synoptic conditions leading to such intense and damaging storms. As part of this project, tools for short-term predictions (nowcasts) of intense convection across the Mediterranean and Europe, and long-term forecasts (a few days) of the likelihood of intense convection, were developed and employed. The project also focused on educational outreach through a special Web site http://flashproject.org supplying real-time lightning observations, real-time experimental nowcasts, medium-range weather forecasts and educational materials. While flash floods and intense thunderstorms cannot be prevented, long-range regional lightning networks can supply valuable data, in real time, for warning the public, end-users and stakeholders of imminent intense rainfall and possible flash floods.

The meteorological model MM5 is applied operationally for the area of north-western Greece for one-year period (1 June 2007–31 May 2008). The model output is used for daily weather forecasting over the area. An early warning system is developed, by dividing the study area in 16 sub-regions and defining specific thresholds for issuing alerts for adverse weather phenomena. The verification of the model is carried out by comparing the model results with observations from three automatic meteorological stations. For air temperature and wind speed, correlation coefficients and biases are calculated, revealing that there is a significant overestimation of the early morning air temperature. For precipitation amount, yes/no contingency tables are constructed for 4 specific thresholds and some categorical statistics are applied, showing that the prediction of precipitation in the area under study is generally satisfactory. Finally, the thunderstorm warnings issued by the system are verified against the observed lightning activity.

In this study the relationship between lightning and simulated microphysical parameters of clouds, is examined. In order to investigate such a relationship, a number of cases with significant lightning activity that occurred during the wet period of the year over the central and eastern Mediterranean have been selected, based on the lightning activity reported by the ZEUS lighting detection network, operated by the National Observatory of Athens. For the same cases, simulations with the non-hydrostatic MM5 model were performed with the aim of reproducing the dynamical and microphysical parameters associated with the weather systems that produced lightning. The analysis showed that the temporal distribution of convective rainfall is not well correlated with that of lightning, while on the contrary, the temporal distribution of the simulated concentrations of solid hydrometeors correlates well with lightning and there is also a general coincidence of their maxima. Further, it was shown that the best correlation was found during the development stage of the storms, while during the decay phase the number of lightning decreases much faster that the simulated concentrations of solid hydrometeors.

During the period 21–22 January 2004, an explosive cyclogenesis event occurred over the Aegean Sea. The minimum observed pressure was 972 hPa, a value which is among the three lowest observed over the entire Mediterranean Sea during the last 40 years. This paper is devoted to the investigation of the conditions that contributed to the rapid development of this low-pressure system through analysis of both observations and model results. It was found that the rapid development of the cyclone was associated with a two-trough system that, under the influence of a very intense upper-level jet, merged into a single trough and then acquired a negative tilt. Sensitivity tests with the MM5 model showed that the upper-level dynamic forcing was the main factor that led to the explosive cyclogenesis, while surface sensible and latent heat fluxes contributed to the cyclone deepening mainly during the storm's mature phase. Copyright © 2007 Royal Meteorological Society

A combined modelling system consisting of a meteorological model (Colorado State University/ Regional Atmospheric Modelling System) and a transport package (Hybrid Particle and Concentration Transport Model) is used. The simulations were performed using two types of model initialisation: the first with ECMWF gridded analysis data and the second with one sounding profile. The modelling system has been used to simulate an important air-pollution episode in the Athens urban area. This area is characterised by complex and variable topographic features, and the associated local atmospheric circulations play a significant role in defining the transport and dispersion conditions over the area. The advantages and shortcomings of both types of initialisation, and more specifically the capability of the model to represent and reproduce the local-scale conditions and the dispersion of air pollutants, are discussed.