Rainfall thresholds and flood warning: an operative case study

Abstract

Abstract. An operative methodology for rainfall thresholds definition is illustrated, in order to provide at critical river section optimal flood warnings. Threshold overcoming could produce a critical situation in river sites exposed to alluvial risk and trigger the prevention and emergency system alert. The procedure for the definition of critical rainfall threshold values is based both on the quantitative precipitation observed and the hydrological response of the basin. Thresholds values specify the precipitation amount for a given duration that generates a critical discharge in a given cross section and are estimated by hydrological modelling for several scenarios (e.g.: modifying the soil moisture conditions). Some preliminary results, in terms of reliability analysis (presence of false alarms and missed alarms, evaluated using indicators like hit rate and false alarm rate) for the case study of Mignone River are presented.

Rainfall threshold definition using an entropy decision approach and radar data

“…With this approach, a critical rainfall threshold is obtained which no longer refers to the critical discharge but to the different return periods (i.e., 2, 5, 10, 20, 50, 100 yr). A description of the procedures which must be carried out in order to evaluate the critical rainfall thresholds in different situations is reported in Montesarchio et al (2009). The critical reference discharge could be reached and surpassed for different space-time configurations of rainfall fields.…”

“…As input of the rainfall runoff model, synthetic hyetographs with different shapes and durations are used. This is a deterministic approach and has been used in previous work (e.g., Montesarchio et al, 2009); it will be further discussed in Sect. 3.1.…”

“…Hydrometric data were used also to perform the calibration and verification of the rainfall-runoff model, which is based on radar data. A summary of flood events affecting the Mignone River basin from 1999 to 2007 can be found in Montesarchio et al (2009). Hydrometric and pluviometric data of the years 2009 and 2010 are used to add a short validation period to test the efficiency of rainfall thresholds based warning system.…”

“…Radar data provide fine space-time resolution rainfall, useful for hazard nowcasting (Lombardo et al, 2006b), flood forecasting Montesarchio et al, 2009) and sewer system monitoring (Giulianelli et al, 2006). On the other hand, despite continuous technological progress, the available instruments used to measure rainfall across several spatio-temporal scales remain inaccurate , implying inaccuracies in rainfall estimates.…”

Outcomes of the 9th EGU Plinius Conference on Mediterranean Storms (2007)

“…As a test case, the authors study an extreme flash flood in the Fella catchment, eastern Italian Alps, on 29 August 2003. Montesarchio et al (2009) propose an operational methodology for the definition of critical rainfall thresholds for possible flood occurrence, and show an application to the Mignone River basin, central Italy. Manfreda (2008) proposes an analytical approach for the description of the soil-water balance and runoff generation dynamics in a humid catchment.…”