Integrated Vapour Transport Climatology 1994–2023 and a Case Study of an Atmospheric River Event in November 2023 in Bulgaria

Abstract

In recent decades, floods and droughts have intensified globally, with Atmospheric Rivers (ARs) being major vapour transport streams that cause extreme precipitation in regions like California, but their impact in Bulgaria remains largely unexplored. This study aims to establish the climatology of Integrated Vapour Transport (IVT) over Bulgaria for the period 1994–2023 and to present a case study of a high-impact weather event. The analysis reveals a distinct seasonal cycle, with maximum IVT values in summer and minimum values in winter. In 2023, monthly mean IVT exceeded the 30-year climatological mean in eight months, with the strongest anomalies observed in autumn – particularly in September and November. On 4th November 2023, a cyclone brought heavy rainfall to Bulgaria, associated with a pronounced IVT anomaly and a well-defined AR structure. IVT anomaly maps and vertical profiles of water vapour transport indicate a moisture plume extending from the Atlantic Ocean, across the Mediterranean Sea, toward the Balkans. This work provides the first long-term climatological assessment of IVT and ARs over Bulgaria, filling a regional research gap and offering new insights into moisture transport and its role in Southeastern Europe's hydrometeorology.