Drought hazard in Bulgaria under conditions of climate change

The Shared Socio-economic Pathways (SSPs) presented in the Sixth Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) indicate that increased variability and more frequent extremes in precipitation are expected to raise the risk of droughts and floods in South-Eastern Europe. According to climate projections, the potential increase in precipitation in the region is insignificant, while the rising temperatures and the associated increase in potential evapotranspiration may lead to a substantial intensification of drought severity in the future. This study reviews previous research on droughts in Bulgaria and the analytical methods applied, thereby justifying the selection of the proposed methodological approach based on the Standardized Precipitation Evapotranspiration Index (SPEI-12 and SPEI-48). The SPEI data were obtained from the Global SPEI Database and cover the period from 1950 to 2024. The spatial characteristics of the index for the territory of Bulgaria are represented by grid cells with a spatial resolution of 0.5 degrees. The study examines changes in drought conditions across Bulgaria over the period 1950–2024, using SPEI-48 data. Long-term fluctuations in average SPEI values reveal a pronounced negative trend since 1984. The index reached its lowest value during the period 2000–2003 (−1.6), which is classified as a severe drought. Average SPEI-48 values range between 0.8 and −0.8 across the decades from 1950 to 2024, and have remained predominantly negative over the last five decades. In this context, the study highlights the need to implement measures for climate change adaptation and to address the increasing risk of drought.