Estimation of flood risk thresholds in Mediterranean areas using rainfall indicators: case study of Valencian Region (Spain)

Flood risk research applications are important to management work. These applications consist of correctly alerting the authorities about adverse events, based on rainfall thresholds adjusted to reality (to detect phenomena without creating alarmism). This paper addresses the detection of rainfall indicators and estimates their risk thresholds in Valencia (Mediterranean coast of Spain) between 1997 and 2007. It is based on the comparison of two databases: (1) a rainfall database, developed at the University of Valencia, and (2) a flood damage database, developed by the Civil Defence Department. It also assesses the accuracy of current alarm thresholds in the Plan Meteoalerta, the Spanish National Programme for Forecasting Adverse Weather Conditions. Results show that the greatest losses are correlated with total event rainfall (r (2) = 0.92); intensity in 1 h (r (2) = 0.82); and accumulated rainfall over 6 h (r (2) = 0.86) and 12 h (r (2) = 0.84). Generally speaking, cumulative rainfall up to 130 mm may cause slight damage, which can become moderate if rainfall reaches 298 mm. When rainfall goes above 466 mm, damage can be significant. By category, the lowest thresholds correspond to urban areas, followed by personal damage and damage to infrastructures. In terms of the number of warnings put forward by the active Plan Meteoalerta, results have shown that, in general, all the thresholds could be increased.