The Role of Atmospheric Processes Associated with a Flash-Flood Event Over Northwestern Turkey

Abstract

This study investigates the atmospheric mechanisms triggering flash-flood event in Thrace Basin of Turkey on November 27, 2018. Underestimation of this extreme precipitation amounts by NWP global and regional models (i.e. ECMWF, ALARO, WRF) and other meteorological difficulties (i.e. complex topography, land-sea interactions) in weather forecasting disabled disaster risk reduction before the event occurred. Detailed synoptic, thermodynamic, in-situ, and remote sensing analyzing results showed that significant amount of moisture during the afternoon times of the day was transferred to the atmosphere (from ground to 300-hPa) as a consequence of the excessive heating of sea surface temperatures (SSTs) of the Aegean Sea (16.5 °C in Ayvacik-Gulpinar place, 0.9 °C above its long-term normals). Strong southwesterly wind speeds associated with slow meridional movement of mid-latitude cyclone from its origin to the Eastern Mediterranean (EM) enabled transferring of relatively warm moist air to the land areas of Thrace Region (> 300 km fetch distance). Strong updraft and instability conditions under developed a supercell resulted with lightning (totally 63 cloud-to-ground and 59 intra cloud) and heavy rainfall especially Suloglu, Kofcaz, and Edirne settlements with the 12-hour total amounts 160.0, 123.0, and 97.4 mm (rainfall return period ~ 100 years), respectively. Flash-flood event caused numerous injuries and the death of a person and damaged, automobiles, houses, crops, and infrastructure of the Edirne and its neighboring settlements. From Showalter, K, Total of Totals, SWEAT, and CAPE instability indices; SWEAT is most appropriate to represent high possibility of occurrence of severe thunderstorms over the Edirne province owing to low-level moisture, warm air advection and low and mid-level wind speed terms in its equation.