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The polar front jet and the subtropical jet, usually separated, are rarely superposed at the same latitude over the greater Mediterranean region, resulting in intense cyclogenesis. The objective of this study is to identify the superposition of the two jets over the Mediterranean on a climatological basis and the possible association with high-impact weather events with the aid of satellite-based indicators. The results show that, indeed, the satellite indicators help in better identifying the area of possible jet superposition. Furthermore, it was found that although jet stream superposition occurs very rarely, it is mostly associated with severe weather events in the surrounding areas. [ABSTRACT FROM AUTHOR]

In recent years, a considerable body of research has demonstrated the suitability of global and regional reanalysis data for human-biometeorological applications. These applications include the assessment of the outdoor thermal environment and the investigation of its relation to human health, especially in areas where the spatial coverage of surface observational networks is sparse. Here, we present the first comprehensive evaluation of the most recent pan-European regional reanalysis, namely the Copernicus European Regional Reanalysis (CERRA) dataset at 5.5 km spatial resolution, in terms of simulating the observed human bioclimate, as expressed by the modified physiologically equivalent temperature (mPET) that is computed through the RayMan Pro model, and its meteorological drivers. The validation was performed over Greece using up to 11 years of records of 2 m air temperature and relative humidity, 10 m wind speed and global solar radiation derived from 35 sites of the nationwide network of surface weather stations operated by the METEO Unit at the National Observatory of Athens. The ERA5-Land dataset at ~9 km spatial resolution, which represents the current state-of-the-art reanalysis, was also compared against the same observations. Our findings show that the CERRA dataset performs significantly better compared to the ERA5-Land reanalysis with respect to the replication of the examined meteorological variables and mPET. The added value of the CERRA data is particularly evident during the warm period of the year and in regions that are characterized by complex topography and/or proximity to the coastline. Combining the CERRA dataset with population and mortality data, we further showcase its applicability for human-biometeorological and heat-health studies at a local scale, using the regional unit of Rethymno (Crete) as a pilot area for the analysis. [ABSTRACT FROM AUTHOR]

Europe has been experiencing an increasing number of sweltering heat waves in recent years. This run of hot extremes induces a significant impact on the human environment, especially in terms of excess mortality, highlighting the urgent need for improved heat-health action planning. This is particularly true in countries situated in the eastern Mediterranean, which is considered a climate change hot spot. To increase preparedness and response to overheating risks, heat-health warning systems (HHWSs) are of vital importance. In this direction, the principal aim of the HEAT-ALARM research project is to provide a novel scientific and technological framework for the development of efficient HHWSs, employing Greece as a testbed. Going beyond the simple notion that outdoor meteorological conditions alone can adequately describe the heat-health nexus, a sophisticated human-biometeorological index, the modified physiologically equivalent temperature (mPET), is used. Advanced statistical models and tools are employed in order to establish a clear link between mPET and excess mortality at regional-unit administrative level. Moreover, urban climate factors produced by combining remote sensing and geographical information system techniques are incorporated into the HHWS via a state-of-the-art numerical weather prediction model. The latter includes a scheme that combines the parameterization and modeling of building effects and energy, respectively, in order to account for the urban indoor thermal conditions and the intra-urban differential heat exposure within the five highest populated cities of Greece (Athens, Thessaloniki, Patras, Heraklion and Larissa). Further, the human body's acclimatization ability is considered, as well as the physiological characteristics of different vulnerable groups of people, including the elderly, women and outdoor workers. The current paper describes the scientific background of HEAT-ALARM and provides preliminary results associated with the project's realization. [ABSTRACT FROM AUTHOR]

The Eastern Mediterranean and Middle East (EMME) region is an exceptionally thermally vulnerable area, projected to suffer from frequent and severe heatwaves in the coming decades. To assess the impacts of climate change on the urban thermal environment in cities, high-resolution numerical simulations are crucial. In this study, the Weather Research and Forecasting (WRF) model is tested in order to progressively downscale the regional scale (12 km) to the local scale (1 km) and thus derive high-resolution data for the 2 m air temperature over Nicosia. Two different simulations were conducted, driven by the ERA5 re-analysis, over a two-month summer period, namely from 15 June to 15 August, 2021, to compare two different urban canopy schemes. The first simulation concerns the implementation of the bulk scheme using the default land cover of MODIS. In the second, the WRF model was coupled with the Single Layer Urban Canopy Model for a better representation of the urban characteristics of Nicosia, and detailed information on the urban form was inserted into the model via the creation of the Local Climate Zones classification scheme. A comparison between the two different physical schemes as well as an evaluation of the simulation results with observation data are performed. [ABSTRACT FROM AUTHOR]