The Mediterranean faces frequent heavy precipitation, deadly heatwaves, and wildfires fueled by its climate. Greece, with its complex topography, experiences severe and extreme weather events that have escalated in recent years and are projected to continue rising under future climate conditions. This paper analyzes severe weather events and trends in Greece from 2010 to 2023, leveraging data from an expanded network of weather stations spanning across Greece, as well as long-term meteorological data from the reference weather station in the center of Athens. The focus includes analysis of heat waves, intense rainfall and droughts, thunderstorms, hail, tornadoes, and fire weather conditions. The societal impact of severe weather events is also discussed. The paper aims to provide both long-term (1901–2023) and recent year analyses (2010–2023). The main results show that between 2010 and 2023, Greece experienced: nearly one heatwave per summer; heavy rainfall events, most common in winter and autumn, showing a significant increase, particularly in the eastern Aegean and western continental Greece; dry spells, which are longest in southern Greece; thunderstorm and hail events peaking in spring and summer; fire weather conditions and risk peaking in southern Greece. Finally, societal impacts from weather hazards have increased in Greece over the past 14 years, with flash floods being the most frequent and damaging events, while public preparedness and effective risk communication remain low.

The air temperature near the Earth’s surface is one of the most important meteorological and climatological parameters. Yet, accurate and timely readings are not available in significant parts of the world. The development and first validation of a methodology for the estimation of the near-surface air temperature (NSAT) is presented here. Machine learning and satellite products are at the core of the developed model. Land Surface Analysis Satellite Application Facility (LSA SAF) products related to Earth’s surface radiation, temperature and humidity budgets, albedo and land cover, along with static topography parameters and weather station measurements, are used in the analysis. A series of experiments showed that the Random Forest regression with 20 selected satellite and topography predictors was the optimum selection for the estimation of the NSAT. The mean absolute error (MAE) of the NSAT estimation model was 0.96 °C, while the mean biased error (MBE) was −0.01 °C and the R2 was 0.976. Limited seasonality was present in the efficiency of the model, while an increase in errors was noted during the first morning and afternoon hours. The topography influence in the model efficiency was rather limited. Cloud-free conditions were associated to only marginally smaller errors, supporting the applicability of the model under both cloud-free and cloudy conditions.

The change in heating and cooling needs of Greece in the near future due to the climate change is assessed in the present study. Global and regional climate models and two different representative concentration pathways (RCPs) are used to simulate the expected change in temperature. A widely used methodology of computation of heating degree days (HDDs) and cooling degree days (CDDs) is employed with a base temperature of 18 °C. In agreement with the expected temperature rise in the near future, an HDD decrease and CDD increase under both RCPs is also expected. The changes under RCP8.5 are stronger compared to those under RCP4.5. Differences related to topography are noted. The HDD decrease is stronger than CDD increase but the relative increase in CDDs is higher than the relative increase in HDDs. The highest absolute decreases in HDDs are expected for February and March while the highest absolute increases in CDDs are expected during the three summer months.

The algorithm of the Convective Rainfall Rate with Microphysical Properties (CRRPh) product of the 2021 version of the Nowcasting and Very Short Range Forecasting Satellite Application Facility (NWC SAF) presents innovative characteristics. It was developed employing principal components analysis to reduce the number of utilized parameters and uses the same mathematical scheme for day and night, simulating the missing visual channels and satellite-derived cloud water path information that is unavailable during nighttime. Applying adequate statistical methodologies and scores and using rain gauge data as ground truth, it is shown that the new algorithm appears to be significantly improved compared to its predecessors in regard to the delineation of the precipitation areas. In addition, it minimizes the day–night difference in the estimation efficiency, which is a remarkable achievement. The new product suffers from slightly higher errors in the precipitation accumulations. Finally, it is shown that topography does not seem to affect the estimation efficiency of the product. In light of these results, it is argued that, overall, the new algorithm outperforms its predecessors and, possibly after adequate adaptations, can be used as a real-time total precipitation product.

<p>This work focuses on the extreme pyroconvective wildfires that impacted southern Greece in early August 2021. These wildfires were unprecedented in extent, intensity, and impacts. They broke out in Attica, Euboea, Elis, Messenia, and Laconia, on August 03 and 04, 2021, and kept burning for several days. Observational evidence indicates that all wildfires exhibited extreme fire behavior, characterized by erratic fire spread, prolific spotting, and the formation of pyroclouds. The factors that contributed to this outbreak of extreme wildfires are sought in the combination of (1) antecedent meteorological conditions that allowed for the accumulation and extreme dry-out of fuels, and (2) concurrent adverse fire weather that enabled the wildfires to couple with the atmosphere and evolve into extreme pyroconvective events. Both topics serve as the motivation of this work, which presents a preliminary analysis of the extreme early August 2021 wildfires in Greece. The analysis was conducted employing ground-based and spaceborne observations. Results indicate the build-up of large potential for the occurrence of extreme wildfires in the affected regions since at least the beginning of the 2021 fire season. Our overarching goal is to consolidate the need for early detection and warning of elevated potential for extreme pyroconvective events, which are becoming a globally increasing concern due to inter alia climate change. The presented work was conducted in the frame of the CLIMPACT and FLAME (project number: 00559) research projects.</p>

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.

The 2021 fire season in Greece was the worst of the past 13 years, resulting in more than 130,000 ha of burnt area, with about 70% consumed by five wildfires that ignited and spread in early August. Common to these wildfires was the occurrence of violent pyroconvection. This work presents a meteorological analysis of this outbreak of extreme pyroconvective wildfires. Our analysis shows that dry and warm antecedent weather preconditioned fuels in the fire-affected areas, creating a fire environment that alone could effectively support intense wildfire activity. Analysis of surface conditions revealed that the ignition and the most active spread of all wildfires coincided with the most adverse fire weather since the beginning of the fire season. Further, the atmospheric environment was conducive to violent pyroconvection, as atmospheric instability gradually increased amid the breakdown of an upper-air ridge ahead of an approaching long-wave trough. In summary, we highlight that the severity and extent of the 2021 Greek wildfires were not surprising considering the fire weather potential for the period when they ignited. Continuous monitoring of the large- and local-scale conditions that promote extreme fire behavior is imperative for improving Greece’s capacity for managing extreme wildfires.

In this study, atmospheric dynamical processes, which govern the intensification of wildfire activity and the associated increase in low-level ozone concentrations, were studied using images, advanced products and vertical profiles derived from satellite observations. The analyses confirm that the influence of deep stratospheric intrusions, identified in the satellite water vapor imagery, on a fire-risk area contributes to the increase in fire activity. The depth of dry stratospheric intrusions, the associated synoptic evolution and the enhanced low-level ozone concentrations caused by vertical transport of stratospheric air and/or related to biomass burning emissions were analyzed using satellite measurements from SEVIRI, IASI and CrIS instruments, complemented with surface observations near the wildfires’ locations. It is shown that the spatial and vertical resolutions of these soundings provide a way of identifying areas of enhanced ozone downwind of wildfires. Influences of the upper-troposphere dynamics and the wind field evolution as factors of uncertainty and complexity in studying the ozone production from wildfire emissions are considered. The combination of satellite soundings and satellite estimations of fire radiative energy and WV imagery may contribute to better understand the ozone enhancement associated with stratospheric intrusion and wildfire emissions.

The NWCSAF (Support to Nowcasting and Very Short Range Forecasting Satellite Application Facility) software package provides operational products that ensure the optimum use of meteorological satellite data in Nowcasting and Very Short Range Forecasting. The National Observatory of Athens operates NWCSAF since 2016. The rainfall estimates obtained by the Convective Rainfall Rate (CRR) nighttime algorithm and the Convective Rainfall Rate from Cloud Physical Properties (CRR-Ph) algorithm of the 2016 version are verified against rainfall observations provided by the dense network of automated surface weather stations operated by the National Observatory of Athens (NOA) for a full year. For the verification a temporal upscaling to 30 min was applied to all datasets. Overall, CRR overestimates the extent of the precipitation areas while at the same time it underestimates the precipitation totals. CRR-Ph clearly outperforms the CRR nighttime algorithm regarding the accurate delineation of precipitation areas but it overestimates the precipitation totals. Heavier precipitation is consistently detected by both algorithms although the false alarms rate is high. Seasonal variations are found, with the most important the poorer estimation performance during spring.

Aim of the study is to examine the potential utilization of satellite precipitation data to estimate the peak discharges of flash floods in ungauged Mediterranean watersheds. Cumulative precipitation heights from local rain gauge and the GPM-IMERG were correlated in a scatter plot. The calculated linear equations were used to adjust the uncalibrated GPM-IMERG precipitation data in Thasos island (Northern Greece), to investigate the mechanisms of the flash floods recorded in November 2019 and to evaluate the significance of satellite precipitation data in hydrological modeling. The uncalibrated GPM-IMERG precipitation failed to explain the flash floods phenomena. The rain gauge data are reliable to accurately predict the peak discharges only in cases, where the rain gauges are within the study area. The strong correlation between ground rainfall data and satellite spatiotemporal precipitation data (R2 > 0.65), provides linear regression equations that, through their extrapolation and appliance to the rest of the flooded area, could adjust and correct the satellite data, optimizing the efficiency and accuracy of flash flood analysis, especially in ungauged watersheds. The proposed methodology could highly contribute to the optimization of flood mitigation measures establishment, flood risk assessment, hydrological and hydraulic simulation of flash flood events in ungauged watersheds.

This paper is devoted to the discussion of the practice of storm naming that has been initiated in January 2017 for the first time in the Eastern Mediterranean Region. Namely the METEO Unit at NOA, taking into consideration that storm naming facilitates meteorologists, researchers, authorities, civil protection officers, the media and citizens to communicate the forecasts of high-impact weather events, started storm naming in January 2017 and has named 35 storms up to September 2021. The criteria of storm naming are discussed, and a synopsis of the events is presented. The monthly distribution shows that 57% of the named storms occurred during the winter period, with January being the month with the highest percentage of occurrence of named storms (28%). The impact of storm naming on citizens risk perception and increased awareness has been also assessed through an internet-based questionnaire that was launched on the fourth year of the storm naming practice in Greece. Overall, results indicate a significant impact of storm naming on the readiness of citizens through the activation of perceptual and cognitive mechanisms.

During February 2019, two severe storms affected the island of Crete, located in south Greece. Both storms produced excessive rainfall, provoking severe damages, especially in the western part of Crete. The role of the prevailing synoptic patterns and the interaction of the flow with the high mountains of Crete were investigated. For this purpose, a variety of observational and numerical model data were exploited, including data from a dense rain gauge network, satellite imagery, and model analysis of various parameters describing the stability of the impinging flow. The first storm was a long-lasting event, with convective outbreaks embedded in a more stratiform rainfall pattern. The second storm was brief but mostly convection dominated. The analysis of the available data underlined the role of the low-level convergence upstream of the mountains during both storms, highlighting similarities and differences, as well as the role of the stability of the impinging flow. High soil moisture content was also evidenced as a key ingredient for the severe flooding that occurred during the second storm. This work complements similar studies on the role of Mediterranean islands and their topography on the spatial and temporal distribution of extreme rainfall.

This paper discusses the main achievements of DISARM (Drought and fIre ObServatory and eArly waRning system) project, which developed an early warning system for wildfires in the Eastern Mediterranean. The four pillars of this system include (i) forecasting wildfire danger, (ii) detecting wildfires with remote sensing techniques, (iii) forecasting wildfire spread with a coupled weather-fire modeling system, and (iv) assessing the wildfire risk in the frame of climate change. Special emphasis is given to the innovative and replicable parts of the system. It is shown that for the effective use of fire weather forecasting in different geographical areas and in order to account for the local climate conditions, a proper adjustment of the wildfire danger classification is necessary. Additionally, the consideration of vegetation dryness may provide better estimates of wildfire danger. Our study also highlights some deficiencies of both EUMETSAT (Exploitation of Meteorological Satellites) and LSA-SAF (Satellite Application Facility on Land Surface Analysis) algorithms in their skill to detect wildfires over islands and near the coastline. To tackle this issue, a relevant modification is proposed. Furthermore, it is shown that IRIS, the coupled atmosphere-fire modeling system developed in the frame of DISARM, has proven to be a valuable supporting tool in fire suppression actions. Finally, assessment of the wildfire danger in the future climate provides the necessary context for the development of regional adaptation strategies to climate change.

The Price-Rind 92 parameterization (Price and Rind, 1992) that utilizes cloud top height as predictor for the estimation of lightning density is widely used by modelers in an attempt to forecast electrical activity in thunderstorms. In the present paper new parameterizations for the estimation of lightning density of convective clouds are formulated. LINET lightning data, NWC SAF (Satellite Application Facility on support to Nowcasting and Very Short-Range Forecasting) products and ERA-Interim (ECMWF-Re Analysis) data, covering the summer of 2016 over continental Europe, are used. The proposed models estimate the lightning density of convective clouds, using cloud top height, cloud top pressure and cold cloud depth as predictors. Model efficiency statistics calculated over an independent dataset, suggest that the proposed models can be considered successful over the specific area (continental Europe) and period (summer). The new cloud top height model differs from the PR92 and other parameterizations, which is not an unexpected result, since every model has its own characteristics, strengths and weaknesses. The new parameterizations could be utilized in numerical model simulations to produce quantitative estimations of the amount of strokes over convective areas.

Eumetsat's Satellite Application Facility on support to Nowcasting and Very Short-Range Forecasting (SAF NWC) products are used by forecasters for various nowcasting purposes. The validation of these products has been performed with good results over different regions and with specific configurations. In the present work, a first step towards the validation of a precipitation SAF NWC Meteosat Second Generation (MSG) product over the Greek area is performed. The Accumulated Convective Rainfall Rate (ACRR) product during the warm months of 2015 is compared against two types of observational data: Rainfall measurements from the meteorological stations network and lightning data from the ZEUS Very Low Frequency (VLF) detection system, both deployed and maintained by the National Observatory of Athens. The open-source Weather Research and Forecasting Model (WRF) is employed to provide the necessary numerical weather prediction input data for the generation of the SAF products.

An analysis of selected spatiotemporal characteristics of isolated thunderstorms in relation to cloud-to-ground (CG) lightning over part of the eastern Mediterranean is performed. The purpose of the study is twofold: to better understand and improve the basic knowledge of the physical mechanisms of the phenomenon and to offer new means of nowcasting the lightning activity in such thunderstorms. Meteosat Second Generation (MSG) Rapid Scan Service (RSS) infrared imagery which offers the option of tracking the examined storms with a time frequency of 5 minutes is one of the two utilized datasets, the other being ZEUS very low frequency (VLF) lightning detection system's CG discharge data. It was shown that a cloud top temperature of about -20 degrees C is required for the onset of lightning activity. A rapid drop of the cloud-top temperature of about 11 degrees C in 5 minutes on average is observed a few minutes before or during lightning initiation. The maximization of the activity is usually quite close to the overall minimum cloud-top temperature of the cell. A temperature increase of 3.5 degrees C from this overall minimum can mark the end of the activity, which is also associated to the time evolution of the cell's horizontal extent. In fact, after the cell's horizontal area stops to increase and/or starts to gradually diminish, CG lightning activity is expected to stop.

Shipping is a growing transport sector representing a relevant share of atmospheric pollutant emissions at global scale. In the Mediterranean Sea, shipping affects air quality of coastal urban areas with potential hazardous effects on both human health and climate. The high number of different approaches for investigating this aspect limits the comparability of results. Furthermore, limited information regarding the inter-annual trends of shipping impacts is available. In this work, an approach integrating emission inventory, numerical modelling (WRF-CAMx modelling system), and experimental measurements at high and low temporal resolution is used to investigate air quality shipping impact in the Adriatic/Ionian area focusing on four port-cities: Brindisi and Venice (Italy), Patras (Greece), and Rijeka (Croatia). Results showed shipping emissions of particulate matter (PM) and NOx comparable to road traffic emissions at all port-cities, with larger contributions to local SO2 emissions. Contributions to PM2.5 ranged between 0.5% (Rijeka) and 7.4% (Brindisi), those to PM10 were between 0.3% (Rijeka) and 5.8% (Brindisi). Contributions to particle number concentration (PNC) showed an impact 2-4 times larger with respect to that on mass concentrations. Shipping impact on gaseous pollutants are larger than those to PM. The contribution to total polycyclic aromatic hydrocarbon (PAHs) concentrations was 82% in Venice and 56% in Brindisi, with a different partition gas-particle because of different meteorological conditions. The inter-annual trends analysis showed the primary contribution to PM concentrations decreasing, due to the implementation of the European legislation on the use of low-sulphur content fuels. This effect was not present on other pollutants like PAHs. (C) 2016 Elsevier Ltd. All rights reserved.

The development and efficiency assessment of a lightning activity nowcasting tool is presented. The tool employs MSG IR imagery and real-time lightning data provided by ZEUS network to nowcast the manifestation of lightning activity over the Greek mainland for a time span of 1h. The efficiency of the tool is assessed for 20days with widespread lightning activity observed during the warm period of the year through a verification procedure that computes a collection of appropriate statistics for selected areas. The analysis of these statistics shows that the tool estimates successfully almost 80% of the upcoming activity. The false alarm rate is close to 40%, while a small overestimation is evident. Since the adverse effects of a case of missed activity are much more than that of a false alarm, the tool is considered successful and fit for operational use.