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Popular Science: Is the gloomy atmosphere of Transylvania disappearing?

Fog is a phenomenon that influences many areas, yet is often neglected. Fog occurrence significantly affects water balance, decreases visibility and affects atmospheric deposition of pollutants. Therefore, it has a significant impact on the landscape and ecosystem. At the same time, it is not entirely easy to estimate its occurrence in advance, as there are many influencing factors. An international scientific team led by Iva Hůnová from the Institute for Environmental Studies, Faculty of Science, Charles University has focused on the terrain and its effects on fog occurrence as a very important, yet largely unexplored factor.

The current research builds on earlier studies of Assoc. Prof. Hůnová’s team who carefully focused on the changes and impact on the occurrence of fog, specifically the role of meteorology, air pollution and also long-term trends in Central Europe. They set out for Romania to study the effect of the terrain on fog occurrence, as this is a very suitable area for this purpose. Romania includes various geomorphological features from the lowlands at the Black Sea shore to the hillsides to the high, steep peaks in the Carpathians.

Romania’s mountains usually have the highest number of days with fog during the year. In recent years, however, the number of days with fog has decreased. Photo: Zuzana Tomšová.

In order to cover all terrain types, experts examined an extensive set of data from 56 professional meteorological stations located in different natural and geographical conditions at altitudes from 13 m above sea level to 2,504 m above sea level. In addition to the altitude, they also used the slope and landform as basic parameters, which they determined with the help of ArcGIS data. The researchers also used long-term daily records of fog occurrence from the 1981–2017 period. They determined both the influence of the terrain on the average occurrence of fog and the possible changes in the long-term (annual) trend and seasonality. A day was considered as a day with fog when at least one episode with horizontal visibility of less than 1 km occurred. The analyses were performed using two statistical generalised additive models (GAM), which allowed for the exploration of nonlinear trends at all 56 meteorological stations and especially the determination of interactions between individual factors.

The results showed that the occurrence of fog decreased significantly in Romania during the analysed period. The decrease was not homogeneous during the year and was more pronounced in non-winter periods. Altitude generally played a very important role. In general, fog occurrence was more frequent in the mountains, but at the same time, depending on the altitude, fog would also develop differently during the year, with the greatest differences in the summer and autumn. While the effects of other parameters, namely the slope and the landform, proved to be insignificant on their own, they were significant in parsimonious interaction.

The recent study introduced a new approach, which has significant benefits for the research into fog occurrence, as it can be applied to other parts of Europe with similar climatic conditions to determine the behaviour of this, still largely unpredictable, meteorological phenomenon.

Kateřina Fraindová

Hůnová, I., Brabec, M., Malý, M., Dumitrescu, A., Geletič, J. (2021): Terrain and its effects on fog occurrence. Science of the Total Environment 768, 144359. https://doi.org/10.1016/j.scitotenv.2020.144359

Published: Jun 07, 2021 05:05 PM

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