Homogenisation and Trend Analysis of Sunshine Duration in Romania for the 1961–2024 Period

ABSTRACT The study presents the national‐scale homogenisation and trend analysis of sunshine duration (SD) observations across Romania for the period 1961–2024. Daily data from 153 weather stations operated by National Meteorological Administration of Romania were subjected to quality control, gap‐filling and homogenisation using the climatol R package. Outlier detection and Standard Normal Homogeneity Test (SNHT) identified 25 discontinuities, highlighting the importance of quality checks. Following homogenisation, about 52% of daily observations were adjusted or gap‐filled, yielding a consistent, long‐term SD dataset. Trend analysis was conducted with the Mann–Kendall test and Theil–Sen estimator on annual and seasonal scales. Results indicate a general increase in SD, with statistically significant positive trends in winter and spring, modest increases in summer and widespread negative but mostly non‐significant trends in autumn. Comparison with climate normal (1961–1990, 1971–2000, 1981–2010, 1991–2020) reveals coherence with internationally reported dimming, brightening and recent stabilisation phases, including European evidence. The homogenised dataset strengthens the reliability of detected trends, reducing artificial variability from instrumentation changes and measurement errors. Beyond scientific relevance, the dataset provides a robust reference for solar energy assessments, agriculture and climate services in Romania and offers a replicable workflow for homogenisation of other climatological variables in national networks.