Preprints
https://doi.org/10.5194/hess-2020-629
https://doi.org/10.5194/hess-2020-629

  22 Dec 2020

22 Dec 2020

Review status: this preprint is currently under review for the journal HESS.

Hydrometeorological evaluation of two nowcasting systems for Mediterranean heavy precipitation events with operational considerations

Alexane Lovat1, Béatrice Vincendon1, and Véronique Ducrocq2 Alexane Lovat et al.
  • 1DSO Météo France, 42 av. G. Coriolis, 31057 Toulouse cedex 1, France
  • 2DIROP Météo France, 42 av. G. Coriolis, 31057 Toulouse cedex 1, France

Abstract. Heavy precipitation events and subsequent flash floods regularly affect the Mediterranean coastal regions. In these situations, forecasting rainfall and river discharges is crucial especially up to six hours, which is a relevant lead time for emergency services in crisis time. The present study investigates the hydrometeorological skills of two new nowcasting systems: a numerical weather model AROME-NWC and a nowcasting system blending numerical weather prediction and extrapolation of radar estimation called PIAF. Their performance is assessed for 10 past heavy precipitation events that occured in southeastern France. Precipitation forecasts are evaluated at a 15 min time resolution and the availability times of forecasts, based on the operational Météo-France suites, are taken into account when performing the evaluation. Rainfall observations and forecasts were first compared using a point-to-point approach. Then the evaluation was conducted from an hydrologic point of view, by comparing observed and forecast precipitation over watersheds affected by floods. In general, the results led to the same conclusions for both evaluations. On the very first lead times, up to 1 h 15/1 h 30 of forecast, the performance of PIAF is higher than AROME-NWC. For longer lead times (up to 3 h) their performance are equivalent in general. An assessment of river discharges simulated with the ISBA-TOP coupled system, which is dedicated to Mediterranean flash-flood simulations, forced by AROME-NWC and PIAF rainfall forecasts, was also performed on two exceptional past flash flood events. The results obtained for these two events show that using AROME-NWC or PIAF rainfall forecasts is promising for flash-flood forecasting in terms of peak intensity, timing, and first rise of discharge, with an anticipation of these phenomena that can reach several hours.

Alexane Lovat et al.

 
Status: open (extended)
Status: open (extended)
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Alexane Lovat et al.

Alexane Lovat et al.

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Short summary
The hydrometeorological skills of two new nowcasting systems for forecasting Mediterranean intense rainfall events and floods are investigated. The results reveal that up to 1 h 15/1 h 30 of forecast, the performance of the nowcasting system blending numerical weather prediction and extrapolation of radar estimation is higher than the numerical weather model. For lead times up to 3 h their skills are equivalent in general. Using these nowcasting systems for flash-flood forecasting is also promising.