Meteorological and physical background
Flash floods and urban floods that occur in just a few hours are often the result of thunderstorms or convective storms that are quasi-stationary, i.e., that spend most of their lifetime in approximately the same area and that occur repeatedly, following each other, with each of them reaching maturity and the maximum amount and intensity of precipitation (i.e., maximum rainfall rate) at approximately the same location. Such a series of convective cells results in the so-called Train effect. Exactly such a situation occurred in the evening hours of 28 September in Istria and around the city of Rijeka.
More information about Train effect phenomena can be found in the SATMANU Conceptual model Cumulonimbus (Cb) and Mesoscale convective system (MSC), in the Special Investigation chapter.