EVALUATION OF A NONHYDROSTATIC MESOSCALE MODEL FOR DISCHARGE

EVALUATION OF A NON-HYDROSTATIC MESOSCALE MODEL FOR DISCHARGE FORECASTING K. Chancibault, V. Ducrocq, F. Habets CNRM/GAME, Météo-France S. Anquetin, G-M. Saulnier CNRS, LTHE WSN 05, Toulouse, France, 5 -9 September 2005 1

INTRODUCTION • Flash-floods in Southeastern France : – – • Quasi-stationnary MCS => high cumulative rainfall amounts (>200 mm/day) Small mountainous basins (200 – 2500 km²) => short lagtime (<12 hrs) Next NWP models : non-hydrostatic high-resolution model (AROME) Meso-NH or AROME Meteorological model 1 -way TOPMODEL 2 -way Hydrological model 1. One-way coupling : 8 -9 September 2002 case 2. Two-way coupling : configuration WSN 05, Toulouse, France, 5 -9 September 2005 2

ONE-WAY COUPLING • The hydrological model : TOPMODEL (Beven and Kirkby, 1979) – – – DTM : 50 m 1 model / basin 9 basins (200 km²- 2200 km²) Calibration (4 parameters) Time step : 1 hour Areal rainfall depths ARDECHE Vogüé * CEZE GARD St Martin * Alès * La * Anduze Roque * Boucoiran Quissac* * Remoulins * * VIDOURLE Sommières WSN 05, Toulouse, France, 5 -9 September 2005 3

ONE-WAY COUPLING Rainfall data • Simulated rainfall : – Meso-NH (Lafore et al, 1998), non-hydrostatic mesoscale model at 2. 4 km – Same physical package and resolution as AROME – Initial conditions : mesoscale initialization (surf obs + radar + IR sat data) from Ducrocq et al ( 2000) • Interpolated (kriging method) rain-gauge data WSN 05, Toulouse, France, 5 -9 September 2005 4

ONE-WAY COUPLING • Case study : 8 -9 September 2002 – 24 casualties – Damage : 1. 2 billion euros mm 10 Phase I 50 100 200 Phase II +Nîmes 300 Phase III +Nîmes 12 -22 UTC, 12 -22 08/09/02 UTC 22 -04 UTC, 08 -09/09/02 22 -04 UTC Cumulated rainfall (Nîmes radar) WSN 05, Toulouse, France, 5 -9 September 2005 +Nîmes UTC 04 -12 UTC, 04 -12 09/09/02 Delrieu et al (2005) 5

ONE-WAY COUPLING • Meso-NH simulations results OBS OBS mm Phase I: 12 -22 UTC Phase II: 22 -04 UTC Phase III: 04 -12 UTC SIMU Cumulated rainfall WSN 05, Toulouse, France, 5 -9 September 2005 SIMU 6

ONE-WAY COUPLING • Meso-NH simulations results Ardèche An Alè s Vo güé St M arti n duz e Bou co Rém iran oul ins La Roq ue res miè c Som Vidourle Qu OBS Gard issa mm Cèze SIMU Cumulated rainfall during the phase I WSN 05, Toulouse, France, 5 -9 September 2005 Simulated rainfall depths errors on the phase I 7

ONE-WAY COUPLING • Hydrological simulations results Anduze (540 km²) Vogüé (620 km²) observed discharges Simulated discharges from : observed rainfall simulated rainfall WSN 05, Toulouse, France, 5 -9 September 2005 8

TWO-WAY COUPLING • Configuration t = 5 min x = 2 -3 km L = 1000 km Meso-NH or Arome flux Wmob t = 5 min x = 2 -3 km L = 1000 km ISBA As TOPMODEL t = 1 h x = 50 m L = 1 km Routing WSN 05, Toulouse, France, 5 -9 September 2005 9

TWO-WAY COUPLING • Idealized simulation Soil water horizontal distribution TOPMODEL 50 m Vogüé m 3/m 3 0. 47 TOPMODEL 50 m Anduze ISBA 2. 5 km 0. 45 0. 43 Soil water increment 0. 41 0. 39 + Vogüé 0. 37 0. 35 0. 33 0. 31 0. 29 WSN 05, Toulouse, France, 5 -9 September 2005 coupleur +Anduze 10

CONCLUSIONS AND OUTLOOKS One-way coupling : • Discharge forecasting needs updated high-resolution forecasted rainfall • Ensemble forecasting rainfalls to perform ensemble discharges forecasting Two-way coupling : • Soil water horizontal distribution was implemented in the SVAT scheme • Soon, routing will be added discharge simulation • Sensitivity studies (e. g. time step, soil depth, …) • Validation for numerous basins of the Southeastern France Applications Ø Validation of high-resolution simulated rainfall Ø Study of the feedback of hydrology to the atmosphere Ø Evaluation of the 2 -way coupling vs the 1 -way coupling WSN 05, Toulouse, France, 5 -9 September 2005 11