Abstract: An automated Early Warning System (EWS) for flash floods is required at national level in Greece; until its development, local authorities are expected to design and implement relatively simple EWS to minimize the current flood risk in their areas. Furthermore, there exist no studies in Greece regarding the flood risk perception of the local population, i.e. their knowledge (based on information and/or education), experience, worry, awareness and preparedness on floods. In this work, we present the main aspects of the design of a relatively simple EWS for flash floods in the town of Mandra in Attica, Greece, which in November 2017 experienced a disastrous flash flood. The design of this EWS is performed within the “National Network on Climate Change and its Impacts” financed by the General Secretariat for Research and Innovation that was initiated in October 2019 and one of its main objectives is the design of an EWS in Mandra that can be used as example for other communities in Greece. The design of this exemplary EWS is based on (1) a literature survey, (2) detailed calculations with integrated hydrological - hydrodynamic models, and (3) a questionnaire survey. The literature survey was performed using international experience, mainly from community based EWS, and scientific publications. The models were employed in the greater area of Mandra using a topographical survey for the creation of the cross-sections for the 1D calculations along the river and a high resolution DTM for the generation of the computational grid for the 2D calculations in the potentially flooded area. The questionnaire survey that was conducted in October and November 2018 in Mandra consisted of 29 questions, mainly of closed type, table or Likert scale of type “yes / no / I do not know”, scale of 5 options and multiple choice; these questions were grouped into 6 sections that dealt with: (1) experience of population on floods, (2) flood awareness, (3) acquired experience from the disastrous flood of November 2017, (4) level of information on floods, (5) preparedness status to deal with floods and (5) preferred mode of warning of impending floods. The main characteristics of the proposed EWS consist of: (1) the hydro-meteorological monitoring network that includes rainfall and stream flow (water level) gauges at monitoring locations that were determined strategically using a Multiple Criteria Analysis, (2) the flash flood forecasting system that involves the application of the integrated model for the determination of the inundation areas (and the associated flood risk), the stream water elevation and its rate of rise, and the estimation of the available flood warning times, and (3) the system for the dissemination and the notification of the warning, whose characteristics were determined using the outcome of the questionnaire survey.     «

Abstract: An automated Early Warning System (EWS) for flash floods is required at national level in Greece; until its development, local authorities are expected to design and implement relatively simple EWS to minimize the current flood risk in their areas. Furthermore, there exist no studies in Greece regarding the flood risk perception of the local population, i.e. their knowledge (based on information and/or education), experience, worry, awareness and preparedness on floods. In this work,...     »