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A 10-year data set of intense Mediterranean cyclones was used for a twofold objective: first to quantify the cyclone's contribution to lightning occurrence in the region and second to investigate potential connection of lightning with cyclones intensity. For this reason, we used cyclone tracks, lightning observations and reanalysis from the European Centre for Medium Range Weather Forecasts, for the 10-year period of 2005-2014. Results showed that intense cyclones provoke <10% of lightning activity over the Mediterranean Sea, however, in certain areas, cyclone contributions might reach 20-30%. The intense cyclones, which are associated with lightning activity close to their centre, constitute about one third (36%) of the total number of tracked cyclones. Therefore two cyclone groups are identified: those associated with and those without lightning. The first group presents in average 35% more ice and 15% more liquid cloud water content within the upper and lower atmospheric levels, respectively, while is related to approximately three times greater values of convective available potential energy in average. Further analysis shows that the intensities of the cyclones in the two groups present no significant differences, suggesting that deep convection may not be a major mechanism for the occurrence of intense Mediterranean cyclones. Finally, we show that cyclones associated with lightning present the highest lightning activity about 6 h prior to the cyclones maximum intensity.

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The Southeast Mediterranean (SEM) is characterized by increased vulnerability to river/stream flooding. However, impact-oriented, operational fluvial flood forecasting is far away from maturity in the region. The current paper presents the first attempt at introducing an operational impact-based warning system in the area, which is founded on the coupling of a state-of-the-art numerical weather prediction model with an advanced spatially-explicit hydrological model. The system’s modeling methodology and forecasting scheme are presented, as well as prototype results, which were derived under a pre-operational mode. Future developments and challenges needed to be addressed in terms of validating the system and increasing its efficiency are also discussed. This communication highlights that standard approaches used in operational weather forecasting in the SEM for providing flood-related information and alerts can, and should, be replaced by advanced coupled hydrometeorological systems, which can be implemented without a significant cost on the operational character of the provided services. This is of great importance in establishing effective early warning services for fluvial flooding in the region.

Heatwave events are of major concern in the global context, since they can significantly impact ecosystems, economies and societies. For this reason, more detailed analyses of the characteristics and trends of heatwaves represent a priority that cannot be neglected. In this study, the interannual and decadal variability of seven indices of heatwaves were investigated during the warmest period of the year (June–August) by using an enhanced resolution reanalysis model (ERA5-Land) over a 71-year period (1950–2020) for the area of Greece. Heatwaves were defined as periods where two thresholds, based on a modified version of the Excess Heat Factor index (EHF) and the 95th percentile of the maximum daily temperature, were exceeded for at least three consecutive days. Greece experiences almost yearly 0.7 heatwaves on average during the whole period of study, while this value has increased by ~80% since 1990. Trend analysis revealed that heatwaves have become more frequent, longer, and more intense since 1950. The percentage of the land area that experiences at least one heatwave per year was almost doubled in the examined period. An increasing trend in the number of heatwaves that occurred in June was identified.

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Abstract. An integrated modeling approach for forecasting flood events is presented in the current study. An advanced flood forecasting model, which is based on the coupling of hydrological and atmospheric components, was used for a twofold objective: first to investigate the potential of a coupled hydrometeorological model to be used for flood forecasting at two medium-size drainage basins in the area of Attica (Greece) and second to investigate the influence of the use of the coupled hydrometeorological model on the precipitation forecast skill. For this reason, we used precipitation and hydrometric in situ data for six flood events at two selected drainage regions of Attica. The simulations were carried out with the Weather Research and Forecasting (WRF) model (WRF-only) and the WRF-Hydro system in a fully coupled mode, under which surface, subsurface, and channel hydrological processes were parameterized at a fine-resolution grid of 95 m approximately. Results showed that the coupled WRF-Hydro system was capable of producing the observed discharge during the flood episodes, after the adequate calibration method applied at the studied basins. This outcome provides confidence that the model configuration under the two-way atmospheric–hydrological coupling is robust and, thus, can be used for operational flood forecasting purposes in the area of Attica. In addition, the WRF-Hydro model showed a tendency to slightly improve the simulated precipitation in comparison to the precipitation produced by the atmospheric-only version of the model (WRF), demonstrating the capability of the coupled WRF-Hydro model to enhance the precipitation forecast skill for operational flood predictions.