REVISITING CLIMATE NORMALS: EVIDENCE OF A REGIME SHIFT, FOREST FIRE ACTIVITY AND IMPLICATIONS FOR FOREST RESOURCES IN SOUTHWESTERN BULGARIA

Abstract

The present study aims to assess whether the transition between the climate normals 1961–1990 and 1991–2020 reflects a statistically significant change in the climatic regime in Southwestern Bulgaria and to examine the relationship between this change and the climatic conditions asso-ciated with the occurrence of forest fires. The analysis is based on temperature and precipitation data from two meteorological stations with contrasting characteristics—Sandanski (lowland) and Musala (high-mountain)—for the period 1961–2024, as well as on forest fire data from the Sandanski region for the period 2000–2025. Trend analysis methods (Mann–Kendall and Sen’s slope), the De Martonne aridity index, and change-point detection methods (CUSUM and Pettitt test) were applied. The results reveal a clear and statistically significant shift in the temperature regime around 1997 at both stations. For summer temperature, an earlier transition is observed in Sandanski, around 1989. The comparison between the climate normals 1961–1990 and 1991–2020 indicates an increase in mean annual temperature of approximately 0.8°C, with the most pronounced warming occurring during summer (+1.6°C). Precipitation exhibits weaker and spatially variable changes, with no statistically significant shift detected in summer precip-itation. The De Martonne index shows elevation-dependent sensitivity, with a tendency toward drier conditions observed at Musala. The analysis of forest fires indicates a strong positive re-lationship between summer temperature and fire activity, while precipitation and aridity show a weaker influence. The results suggest that the contemporary climate normal reflects a real change in the climatic regime, which has direct implications for wildfire risk in the region. These findings are relevant not only for wildfire risk assessment, but also for the sustainable management of forest resources and the long-term security of wood raw material supply in climate-sensitive regions.