Can Rainfall Forecasts from Global NWP Model Ensembles be Used to Detect Areas at Flash Flood Risk? Developing a rainfall-based flash flood forecasting system over a continuous global domain, up to medium range leads.

Oral Presentation

Flash floods are one of the most devastating natural hazards. Every year, they cost thousands of lives and millions of dollars in damaged infrastructure. They can occur in large or small catchments, rural or urban areas, close or away from rivers, and with little to no warning. Some regions might have adapted to protect infrastructure and people against this hazard; however, with climate projections suggesting that extreme rainfall might increase in intensity and frequency, "residual risk" might increase in protected areas while unprotected ones might experience unseen severe losses. Hence, relying on medium-range forecasts that offer good predictions of areas at risk of flash flooding with enough lead time to extend preparedness and action time windows is becoming increasingly important.

This presentation will showcase the most recent developments in the prediction of flash floods over a continuous global domain up to medium-range lead times. We will start by describing the system (ecPoint) used to create the rainfall-based flash flood predictions (ecPoint-Rainfall forecasts) and the warning thresholds that identify areas at risk of flash floods (ERA5-ecPoint rainfall reanalysis). We will also present long-term objective verification results that benchmark our rainfall-based flash flood predictions against competing rainfall forecasts, e.g. ECMWF ensemble forecasts. Through the presentation of case studies, we will explore the added value of using our proposed forecasts in case of low-probability but high-impact flash flood events. We will finally provide practical guidance and recommendations on how to use the flash flood predictions to enable decision-makers to extend their preparedness and action time window.