Spatial and Temporal Variations of Frost-Free Seasons in the Meriç-Ergene Basin

Long-term climate observations reveal a significant upward trend in global average temperatures in recent years. This has led to changes in the timing of frost events throughout the year. Understanding changes in frost-free season length is essential for adapting agricultural production to climatic conditions and minimizing frost-related damage. This study examined the spatial and temporal changes in the parameters of first frost day in autumn (FFA), last frost day in spring (LFS), and frost-free season (FFS) using daily minimum temperature data recorded in the Meriç-Ergene Basin from 1980 to 2024. Spatial distributions were mapped using the inverse distance weighted (IDW) method. Temporal trends were evaluated using the Mann–Kendall test and trend magnitudes were calculated using Sen's slope method. The findings reveal that the average frost-free season in the region lasts approximately 7.6 months. Long-term trend analysis revealed that while LFS shifted backward by approximately 1.6 days per decade, FFA advanced by approximately 5.5 days per decade. Consequently, the frost-free season lengthened by approximately 7.4 days per decade, primarily due to the delayed FFA.