The 8 and 9 September 2002 flash flood event in France: a model intercomparison

Self Cite

Abstract. During the MAP D-PHASE (Mesoscale AlpineProgramme, Demonstration of Probabilistic Hydrological and Atmospheric Simulation of flood Events in the Alpine region) Operational Period (DOP, 1 June-30 November 2007) the most intense precipitation event observed south of the Alps occurred over the Venice Lagoon. In the early morning of 26 September 2007, a mesoscale convective system formed in an area of convergence between a south-easterly low level jet flowing along the Adriatic Sea and a northeasterly barrier-type wind south of the Alps, and was responsible for precipitation exceeding 320 mm in less than 12 h, 240 mm of which in only 3 h.The forecast rainfall fields, provided by several convection resolving models operated daily for the D-PHASE project, have been compared. An analysis of different aspects of the event, such as the relevant mechanisms leading to the flood, the main characteristics of the MCS, and an estimation of the predictability of the episode, has been performed using a number of high resolution, convection resolving models (MOLOCH, WRF and MM5).Strong sensitivity to initial and boundary conditions and to model parameterization schemes has been found. Although low predictability is expected due to the convective nature of rainfall, the forecasts made more than 24 h in advance indicate that the larger scale environment driving the dynamics of this event played an important role in favouring the achievement of a relatively good accuracy in the precipitation forecasts.

Section: Introductionmentioning

confidence: 99%

High resolution simulations of a flash flood near Venice

Davolio

Mastrangelo

Miglietta

et al. 2009

Self Cite

“…Deidda, 2000;Regimbeau et al, 2007), are needed. Several past studies have assessed the value of convection-permitting meteorological forecasts to drive hydrological models dedicated to Mediterranean flash-floods (Anquetin et al, 2005;Chancibault et al, 2006;Vincendon et al, 2009). These studies found that the precipitation underestimation was significantly less marked for the convection-permitting QPF, but there were still uncertainties on rainfall location, which could be detrimental to good discharge forecasting.…”

Section: Introductionmentioning

confidence: 99%

Perturbation of convection-permitting NWP forecasts for flash-flood ensemble forecasting

Vincendon

Ducrocq

Nuissier

et al. 2011

Self Cite

Abstract. Mediterranean intense weather events often lead to devastating flash-floods. Extending the forecasting lead times further than the watershed response times, implies the use of numerical weather prediction (NWP) to drive hydrological models. However, the nature of the precipitating events and the temporal and spatial scales of the watershed response make them difficult to forecast, even using a high-resolution convection-permitting NWP deterministic forecasting. This study proposes a new method to sample the uncertainties of high-resolution NWP precipitation forecasts in order to quantify the predictability of the streamflow forecasts. We have developed a perturbation method based on convection-permitting NWP-model error statistics. It produces short-term precipitation ensemble forecasts from single-value meteorological forecasts. These rainfall ensemble forecasts are then fed into a hydrological model dedicated to flash-flood forecasting to produce ensemble streamflow forecasts. The verification on two flash-flood events shows that this forecasting ensemble performs better than the deterministic forecast. The performance of the precipitation perturbation method has also been found to be broadly as good as that obtained using a state-of-the-art research convectionpermitting NWP ensemble, while requiring less computing time.

“…Correspondence to: M. Kunz (michael.kunz@imk.uka.de) to predict not only the location and the time of convection initiation (Anquetin et al, 2005;Meißner et al, 2007), but also the type and intensity of thunderstorms. Severe thunderstorms are frequently associated with heavy rainfall, hail, or local storms that are a major cause of natural disasters particularly over mountainous terrain that favor the initiation or the triggering of convection (Orville, 1965;Banta, 1990;Barthlott et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

The skill of convective parameters and indices to predict isolated and severe thunderstorms

Kunz¹

2007

165

Abstract. The preconvective environment on days with ordinary, widespread, and severe thunderstorms in Southwest Germany was investigated. Various thermodynamic and kinetic parameters calculated from radiosoundings at 12:00 UTC were verified against subsequent thunderstorm observations derived from SYNOP station data, radar data, and damage reports of a building insurance company. The skill of the convective parameters and indices to predict thunderstorms was evaluated by means of probability distribution functions, probabilities of thunderstorms according to an index threshold, and skill scores like the Heidke Skill Score (HSS) that are based on categorical verification.For the ordinary decision as to whether a thunderstorm day was expected or not, the best results were obtained with the original Lifted Index (80% prediction probability for LI≤−1.73; HSS=0.57 for LI≤1.76), the Showalter Index, and the modified K-Index. Considering days with isolated compared to widespread thunderstorms, the best performance is reached by the Deep Convective Index. For days with severe thunderstorms that caused damage due to hail, local storms or floods, the best prediction skill is found again for the Lifted Index and the Deep Convective Index, but also for the Potential Instability Index, the Delta-θ e Index, and a version of the CAPE, where the lifting profile is determined by averaging over the lowest 100 hPa.