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.
Highlights
Flash floods are among the most devastating natural hazards worldwide, producing important human and socioeconomic losses
The western Mediterranean region is annually affected by several extreme precipitation events which lead to flash flooding
The objective of the present work is to evaluate the predictive skill of two distinct hydrological ensemble prediction systems (HEPSs) generation strategies – accounting for perturbed IC/LBCs (PILB) and mixed physics (MPS) – for three flash-flood episodes over the Agly basin (Fig. 1)
Summary
Flash floods are among the most devastating natural hazards worldwide, producing important human and socioeconomic losses. During the extended warm season, the early intrusion of upper-level cold air masses and the relatively high sea surface temperature boost the convective available potential energy of the low-level Mediterranean warm and moist air. This natural hazard results from the persistence of deep moist convection and intense precipitation over specific hydrographic catchments during several hours. The development and evaluation of the state-of-the-art hydrometeorological forecasting tools is a major issue in the Hydrological cycle in the Mediterranean experiment (HyMeX; Drobinski et al, 2014). How can we improve heavy rainfall process knowledge and prediction? How can we improve hydrological prediction?
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