Precipitation Thresholds for Triggering Floods in the Corgo Basin, Portugal

Abstract

Thresholds based on critical combinations of amount/duration of precipitation and flood events were estimated for the Corgo hydrographic basin, in northern Portugal. Thirty-one flood events in the Corgo basin were identified between 1865 and 2011 from a database of hydrometeorological disasters in Portugal. The minimum, maximum, and pre-warning thresholds that define the boundaries for flood occurrence were determined. The results show that the ratio between the total number of floods and precipitation events exceeding the minimum threshold denotes a relatively low probability of successful forecasting. This result may be due to the reduced number of flooding events in the floods database, which only include floods that caused damage as reported by the media. The estimated maximum threshold is not adequate for use in floods, since the majority of true positives are below this limit. However, and more interestingly, the retrospective verification of the estimated thresholds suggests that the minimum and pre-warning thresholds are well adjusted. Therefore, the application of these precipitation thresholds may contribute to minimize possible situations of pre-crisis or immediate crisis by reducing the flood consequences and the resources involved in emergency response to flood events.

An improved rainfall-threshold approach for robust prediction and warning of flood and flash flood hazards

“…Similar performance has also been observed in the application of rainfall intensity-duration thresholds for floods and landslides worldwide (e.g. Santos and Fragoso 2016;Brunetti et al 2018;Zhao et al 2019). For both upper and lower thresholds, the rainfall peak intensity-duration threshold without the use of tolerance levels presented better results for time steps equal to 1 and 24 h for flash floods and floods, respectively.…”

“…Some studies complemented the rainfall threshold method with probabilities of occurrence to reduce the uncertainties of false alarms for hydrological (e.g. Berti et al 2012;Huang et al 2015;Wu et al 2015;Santos and Fragoso 2016;Brigandì et al 2017). Aiming to reduce the uncertainties in the middle part of the graph but without losing the characteristics of Group 1 and Group 4, two levels of tolerance (sometimes mentioned as exceedance probability) were used in this study to minimise the amplitude between the upper and lower thresholds, e.g.…”

“…One of the first studies using rainfall events to delineate thresholds was due to Caine (1980), who used rainfall peak intensity with different durations for forecasting the occurrence of rainfall-triggered landslides and debris flow in various regions of the world. The empirical methods based on rainfall thresholds have been gradually applied more for landslide warning purposes than for flooding or flash flooding (Diakakis 2012;Papagiannaki et al 2015;Santos and Fragoso 2016). In the area of flood warning, Diakakis (2012) used rainfall intensity-duration parameters to determine the thresholds after adapting the methodologies proposed by Cannon et al (2008) and Guzzetti et al (2008) for landslides.…”

Deriving Rain Threshold for Early Warning Based on a Coupled Hydrological-Hydraulic Model

“…Issuing warning information to the public when forecasted rainfall exceed the derived thresholds is a simple and widely-used method for flood warning. Rainfall thresholds and correspondig warnings contribute to reducing the consequences and the resources involved in emergency response of flood events [16].…”

Application of Machine Learning to Model Wetland Inundation Patterns Across a Large Semiarid Floodplain

“…4. The cumulative rainfall (Ávila et al, 2015;Santos & Fragoso, 2016;Tramblay et al, 2010), runoff, soil moisture, and discharge for 5, 10, 15, 20, 25, and 30 days prior to the captured Landsat inundation scene.…”