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

Geraldo Moura Ramos Filho,Victor Hugo Rabelo Coelho,Cristiano Das Neves Almeida,Emerson Da Silva Freitas,Yunqing Xuan

doi:10.1007/s11069-020-04405-x

Geraldo Moura Ramos Filho, Victor Hugo Rabelo Coelho + Show 3 more

Open Access

https://doi.org/10.1007/s11069-020-04405-x

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Abstract

This paper presents an improved method of using threshold of peak rainfall intensity for robust flood/flash flood evaluation and warnings in the state of São Paulo, Brazil. The improvements involve the use of two tolerance levels and the delineating of an intermediate threshold by incorporating an exponential curve that relates rainfall intensity and Antecedent Precipitation Index (API). The application of the tolerance levels presents an average increase of 14% in the Probability of Detection (POD) of flood and flash flood occurrences above the upper threshold. Moreover, a considerable exclusion (63%) of non-occurrences of floods and flash floods in between the two thresholds significantly reduce the number of false alarms. The intermediate threshold using the exponential curves also exhibits improvements for almost all time steps of both hydrological hazards, with the best results found for floods correlating 8-h peak intensity and 8 days API, with POD and Positive Predictive Value (PPV) values equal to 81% and 82%, respectively. This study provides strong indications that the new proposed rainfall threshold-based approach can help reduce the uncertainties in predicting the occurrences of floods and flash floods.

Highlights

Rainfall is an intermittent phenomenon with irregular spatiotemporal distribution and is able to cause many natural disasters (Dunkerley 2008)
According to the report commissioned by the United Nations Office for Disaster Risk Reduction (UNDRR) in partnership with the Centre for Research on Epidemiology of Disasters (CRED), the last two decades (1998–2017) represent the largest number of records caused by hydrological disasters in history (Wallemacq and House 2018)
Hydrological disasters induced by extreme rainfall events account for 87% of the deaths caused by natural disasters between 1991 and 2012 in Brazil (CEPED 2013)

Summary

Introduction

Rainfall is an intermittent phenomenon with irregular spatiotemporal distribution and is able to cause many natural disasters (Dunkerley 2008). According to the report commissioned by the United Nations Office for Disaster Risk Reduction (UNDRR) in partnership with the Centre for Research on Epidemiology of Disasters (CRED), the last two decades (1998–2017) represent the largest number of records caused by hydrological disasters in history (Wallemacq and House 2018). The same source reported that this type of natural disaster was mainly induced by floods (accounting for 43.4% of all natural disasters) that affected more than 2 billion people in almost all countries in the world, causing more than 142,000 deaths and US$ 650 million of economic losses. Hydrological disasters induced by extreme rainfall events account for 87% of the deaths caused by natural disasters between 1991 and 2012 in Brazil (CEPED 2013)

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