Forensic Hydrology: A Complete Reconstruction of an Extreme Flood Event in Data-Scarce Area

Abstract

On 18 September 2020, the Karditsa prefecture of Thessaly region (Greece) experienced a catastrophic flood as a consequence of the IANOS hurricane. This intense phenomenon was characterized by rainfall records ranging from 220 mm up to 530 mm, in a time interval of 15 h. Extended public infrastructure was damaged and thousands of houses and commercial properties were flooded, while four casualties were recorded. The aim of this study was to provide forensic research on a reconstruction of the flood event in the vicinity of Karditsa city. First, we performed a statistical analysis of the rainfall. Then, we used two numerical models and observed data, either captured by satellites or mined from social media, in order to simulate the event a posteriori. Specifically, a rainfall–runoff CN-unit hydrograph model was combined with a hydrodynamic model based on 2D-shallow water equations model, through the coupling of the hydrological software HEC-HMS with the hydrodynamic software HEC-RAS. Regarding the observed data, the limited available gauged records led us to use a wide spectrum of remote sensing datasets associated with rainfall, such as NASA GPM–IMREG, and numerous videos posted on social media, such as Facebook, in order to validate the extent of the flood. The overall assessment proved that the exceedance probability of the IANOS flooding event ranged from 1:400 years in the low-lying catchments, to 1:1000 years in the upstream mountainous catchments. Moreover, a good performance for the simulated flooding extent was achieved using the numerical models and by comparing their output with the remote sensing footage provided by SENTINEL satellites images, along with the georeferenced videos posted on social media.

Coping with floods: impacts, preparedness and resilience capacity of Greek micro-, small- and medium-sized enterprises in flood-affected areas

“…On 18 September 2020, the greater Karditsa area was hit by an extreme 15-h long rainfall that caused extensive flooding over a number of cities, including Karditsa and Farsala. Both cities suffered severe economic losses and damage to public assets, transportation networks, buildings and agricultural areas, including four human losses (Tegos et al , 2022).…”

Flood damage inspection and risk indexing data for an inventory of bridges in Central Greece

“…A few days after Medicane Ianos struck Greece, on September 17-20 2020, causing severe and widespread damage to infrastructure [1] , [2] , [3] , 5 , 7] , the US GEER Association deployed an interdisciplinary team of researchers and engineers to collect perishable field performance data from the affected regions. The mission made use of remote sensing technologies, employing optical and satellite imagery, in addition to conventional site characterization and structure inspections.…”

Modern Developments in Flood Modelling

“…The paper "Forensic Hydrology: A Complete Reconstruction of an Extreme Flood Event in Data-Scarce Area" [2] by Aristoteles Tegos, Alexandros Ziogas, Vasilis Bellos and Apostolos Tzimas presents a state-of-the-art approach to reconstructing catastrophic flooding events in data-scarce areas. The study focused on the recent catastrophic flooding event, namely medicane Ianos, which substantially affected the town of Karditsa, Greece.…”