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<p>Freezing Level Height (FLH) is the upper boundary in the free atmosphere where water transitions from a liquid or gaseous state to a solid, and it can serve as a valuable indicator of climate change. This research aims to investigate the climatology and changes in FLH across 41 major Romanian cities over a 45-year period (1980–2024). Monthly FLH data were retrieved from the latest ERA5 reanalysis gridded dataset (0.25° × 0.25° horizontal spatial resolution) for each city included in the study. Grid-cell data were directly matched to city centroids. For each city, the ERA5 grid cell whose center was closest to the city centroid was selected for analysis. ArcGIS 10.3.1 software and box-and-whisker plots were used to produce FLH climatologies. Changes in FLH were analyzed using the non-parametric Mann–Kendall test and Sen’s slope estimator. The main findings indicated that cities in southern, southeastern, and western Romania exhibited the highest FLH values across all temporal scales. As expected, higher-elevation cities recorded the lowest FLH values. The seasonal distribution of FLH revealed that the lowest levels occurred in winter, while the highest were observed in summer. FLH during the winter months had a median value ranging from 750 to 1000&#xa0;m, while in summer, the median ranged from 3250 to 3650&#xa0;m. The seasonal and annual distributions of FLH data revealed that summer exhibited a wider range of values, particularly for those below the first quartile across the analyzed locations. The trend analysis revealed a clear and statistically significant increase in FLH across all regions of Romania, ranging from 7.44 to 9.26&#xa0;m per year (on an annual time scale), with only a few non-significant trends observed in winter and spring. The spatiotemporal analysis of changes revealed substantial spatial variability in the magnitude of trends. The strongest trends were observed in summer, while the weakest increases occurred in spring, particularly in central regions. On an annual scale, the most pronounced changes were recorded in the eastern and southeastern areas of Romania.</p>

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Increase in atmospheric freezing level height in Romania over the 1980–2024 period

  • 期刊论文

  • 发表日期：

    2026年4月26日

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  • Adrian Piticar,
  • Alexandru Tudor

摘要

Freezing Level Height (FLH) is the upper boundary in the free atmosphere where water transitions from a liquid or gaseous state to a solid, and it can serve as a valuable indicator of climate change. This research aims to investigate the climatology and changes in FLH across 41 major Romanian cities over a 45-year period (1980–2024). Monthly FLH data were retrieved from the latest ERA5 reanalysis gridded dataset (0.25° × 0.25° horizontal spatial resolution) for each city included in the study. Grid-cell data were directly matched to city centroids. For each city, the ERA5 grid cell whose center was closest to the city centroid was selected for analysis. ArcGIS 10.3.1 software and box-and-whisker plots were used to produce FLH climatologies. Changes in FLH were analyzed using the non-parametric Mann–Kendall test and Sen’s slope estimator. The main findings indicated that cities in southern, southeastern, and western Romania exhibited the highest FLH values across all temporal scales. As expected, higher-elevation cities recorded the lowest FLH values. The seasonal distribution of FLH revealed that the lowest levels occurred in winter, while the highest were observed in summer. FLH during the winter months had a median value ranging from 750 to 1000 m, while in summer, the median ranged from 3250 to 3650 m. The seasonal and annual distributions of FLH data revealed that summer exhibited a wider range of values, particularly for those below the first quartile across the analyzed locations. The trend analysis revealed a clear and statistically significant increase in FLH across all regions of Romania, ranging from 7.44 to 9.26 m per year (on an annual time scale), with only a few non-significant trends observed in winter and spring. The spatiotemporal analysis of changes revealed substantial spatial variability in the magnitude of trends. The strongest trends were observed in summer, while the weakest increases occurred in spring, particularly in central regions. On an annual scale, the most pronounced changes were recorded in the eastern and southeastern areas of Romania.