Articles | Volume 15, issue 8
Research article
19 Aug 2015
Research article |  | 19 Aug 2015

Flash flood occurrence and relation to the rainfall hazard in a highly urbanized area

K. Papagiannaki, K. Lagouvardos, V. Kotroni, and A. Bezes

Abstract. The paper examines the flash flood events that occurred over a decade in the Attica prefecture, the most urbanized region of Greece, with the aim of identifying triggering rainfall thresholds, as well as assessing the effect of rainfall upon the magnitude of the induced damages. The analysis incorporates rainfall records from a network of 28 surface meteorological stations and information on the spatial distribution of the flash flood events that is derived from the active database of damaging weather events maintained by the atmospheric modelling group of the National Observatory of Athens. The main findings concern firstly the relation between the flash flood impact, as measured by the fire service operations in flooded properties, and precipitation in various time intervals. In the period 2005–2014, 48 damaging flash flood events occurred in the target area and caused more than 3500 fire service operations in flooded properties. Most of the events are associated with maximum accumulated rainfall of more than 20 mm in 24 h and 3 mm in 10 min. However, the flash flood impact intensity, as measured by the number of the fire service operations per event, increases significantly above the levels of 60 mm in 24 h and 10 mm in 10 min. Secondly, graphs of rainfall intensity versus duration are developed for 15 sub-areas of Attica in order to define rainfall intensity thresholds for flood triggering at a more local level. It is shown that conclusions regarding the reliability of the estimated thresholds should take into account the representativity of the rain gauges, which is determined by the local network's density, the gauges' location and record length.

Short summary
48 flash flood events in the urban Attica region (2005-2014) resulted in 3,500 fire service operations, mostly in autumn. Events were mostly associated with max accumulated rain over 20mm/24h and 3mm/10min. Impact intensity was particularly high for more than 60mm/24h. Rain intensity thresholds for flood triggering are produced for 15 sub-areas of the Attica region. The quality of the produced thresholds depends on the distribution and density of the rain gauges that cover each sub-area.
Final-revised paper