Comparison of two early warning systems for regional flash flood hazard forecasting

TL;DR

This study compares two real-time flash flood warning systems, one rainfall-based and one runoff-based, evaluating their performance during severe flooding events in Italy to improve hazard forecasting accuracy.

Contribution

It introduces a comparative analysis of two early warning systems for flash floods, highlighting their similarities and differences in regional hazard prediction.

Findings

Both systems perform similarly for large catchments and extreme floods.

The rainfall-based system uses upstream basin rainfall as hazard indicator.

The runoff-based system computes streamflows at pixel scale for hazard assessment.

Abstract

The anticipation of flash flood events is crucial to issue warnings to mitigate their impact. This work presents a comparison of two early warning systems for real-time flash flood hazard forecasting at regional scale. The two systems are based in a gridded drainage network and they use weather radar precipitation inputs to assess the hazard level in different points of the study area, considering the return period (in years) as the indicator of the flash flood hazard. The essential difference between the systems is that one is a rainfall-based system (ERICHA), using the upstream basin-aggregated rainfall as the variable to determine the hazard level, while the other (Flood-PROOFS) is a system based on a distributed rainfall-runoff model to compute the streamflows at pixel scale. The comparison has been done for three rainfall events in the autumn of 2014 that resulted in severe flooding in the Liguria region (Northwest of Italy). The results obtained by the two systems show many similarities, particularly for larger catchments and for large return periods (extreme floods).