Change of winter climate indicators over the Carpathian Basin

Winter phenomena such as fog and freezing rain can significantly impact our daily lives by creating hazardous conditions for transportation and other outdoor activities. Dense fog reduces visibility, leading to traffic disruptions and potential accidents on roads, while freezing rain leaves surfaces with a layer of ice with high risks of falls and slide resulting in personal injuries, in addition, both can disrupt air travel as well. The Carpathian Basin can experience an increased occurrence and persistence of fog due to its unique geographical features, such as low-lying areas, lower wind speed, and river valleys that facilitate temperature inversions. Freezing rain is also prevalent in the Carpathian Basin when raindrops of warmer air masses from the Mediterranean fall through a sub-freezing, inversional layer of air before reaching the ground.

To assess these impacts, we created a methodology based on daily, gridded data sets: we analyzed daily minimum and mean temperature, mean relative humidity, and wind speed for the fog from the best available, homogenized, high-resolution HuClim observational database. For the freezing rain, we collected hourly variables of temperature, total precipitation, and snow from the high-resolution, observation-based but modeled reanalysis of ERA5-Land. For the future, we assessed corrected, daily variables from an ensemble of EURO-CORDEX regional climate model simulations. Several scenarios were taken into account for the effects of human activity: RCP2.6 is a scenario aiming at 2 °C global warming by 2100, RCP4.5 urges strong mitigation from 2040, while RCP8.5 is a non-mitigation scenario.

Results suggest that the number of foggy days slightly decreased over parts of the area of interest in the last few decades, but freezing rain did not change remarkably. Regarding the future, the days with fog would decrease significantly following the RCP8.5 scenario, especially by the end of the 21^st century, while they would not change much with the RCP2.6. These are one of the rare positive impacts of regional climate change, however, it does not compensate for the adverse effects of anthropogenic climate change.