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Abstract

In this study, the oceanic and terrestrial sources of moisture for Bulgaria were identified through the Lagrangian model FLEXPART, which is fundamental to understand the origin and drivers of precipitation variability and extreme events in Bulgaria. The sources were classified into the surrounding land extension of Europe, the north of Africa, the Mediterranean Sea, the Black Sea, the Caspian Sea, and part of the North Atlantic Ocean. The results show that 57% of the total moisture loss over Bulgaria occurs on air masses from oceanic origin, standing out the Mediterranean Sea and the land region encompassing Central and Eastern Europe as the most significant suppliers. The results revealed a positive causal influence and predictability between the contribution from the sources and the precipitation over Bulgaria, highlighting the role of the Mediterranean Sea. The conditional probability of drought in Bulgaria given similar deficits in contributions from the sources, also revealed the major influence of oceanic origin precipitation, particularly the influence from the Mediterranean Sea during extremely dry conditions. Finally, we conducted an attribution analysis of dry/wet conditions trends, which revealed the high predictability value exerted by the Mediterranean Sea, even on seasonal and annual time scales. This analysis also highlights the role of the land-based source that embraces a large part of Europe and the Black Sea.