Evaluation of two hydrometeorological ensemble strategies for flash-flood forecasting over a catchment of the eastern Pyrenees

Abstract

Abstract. This study aims at evaluating the performances of flash-flood forecasts issued from deterministic and ensemble meteorological prognostic systems. The hydrometeorological modeling chain includes the Weather Research and Forecasting Model (WRF) forcing the rainfall-runoff model MARINE dedicated to flash floods. Two distinct ensemble prediction systems accounting for (i) perturbed initial and lateral boundary conditions of the meteorological state and (ii) mesoscale model physical parameterizations have been implemented on the Agly catchment of the eastern Pyrenees with three subcatchments exhibiting different rainfall regimes. Different evaluations of the performance of the hydrometeorological strategies have been performed: (i) verification of short-range ensemble prediction systems and corresponding streamflow forecasts, for a better understanding of how forecasts behave; (ii) usual measures derived from a contingency table approach, to test an alert threshold exceedance; and (iii) overall evaluation of the hydrometeorological chain using the continuous rank probability score, for a general quantification of the ensemble performances. Results show that the overall discharge forecast is improved by both ensemble strategies with respect to the deterministic forecast. Threshold exceedance detections for flood warning also benefit from large hydrometeorological ensemble spread. There are no substantial differences between both ensemble strategies on these test cases in terms of both the issuance of flood warnings and the overall performances, suggesting that both sources of external-scale uncertainty are important to take into account.

Overview towards improved understanding of the mechanisms leading to heavy precipitation in the Western Mediterranean: lessons learned from HyMeX

“…The survey responses provided insights into risk perception and behavioral reactions relative to the space-time distribution of rainfall. Different possibilities of improving hydrometeorological forecasts have also been tested (Roux et al, 2020), pointing out the added value of ensemble strategies with respect to deterministic forecasts. Large meteorological ensemble spreads also allowed better threshold exceedance detection for flood warning.…”

Ensemble flash flood predictions using a high-resolution nationwide distributed rainfall-runoff model: case study of the heavy rain event of July 2018 and Typhoon Hagibis in 2019

“…For ensemble flood predictions, global scale EPSs such as European Centre for Medium-Range Weather Forecasts-Ensemble of forecast (ECMWF-ENS) have been widely used (Alfieri et al 2014). Meanwhile, for ensemble flash flood predictions, some case studies have demonstrate the importance of meso-scale ensemble forecasting (Alfieri et al 2012;Hsiao et al 2013;Roux et al 2020;Ushiyama et al 2014) and their combinations by the Meteorological Ensemble Forecast Processor (MEFP) approach adopted by Hydrologic Ensemble Forecast Service (HEFS) (Brown et al 2014a;Brown et al 2014b).…”

Ensemble Flash Flood Predictions Using a High-Resolution Nationwide Distributed Rainfall-Runoff Model: Case Study of the Heavy Rain Event of July 2018 and Typhoon Hagibis in 2019

“…Meanwhile, for ensemble flash flood predictions, some case studies have demonstrate the importance of meso-scale ensemble forecasting (Alfieri et al 2012;Hsiao et al 2013;Roux et al 2020;Ushiyama et al 2014) and their combinations by the Meteorological Ensemble Forecast Processor (MEFP) approach adopted by Hydrologic Ensemble Forecast Service (HEFS) (Brown et al 2014a;Brown et al 2014b).…”