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On the importance of meteorological downscaling for short, medium and long-range hydrological ensemble prediction over France G. Thirel (1), F. Regimbeau.

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Presentation on theme: "On the importance of meteorological downscaling for short, medium and long-range hydrological ensemble prediction over France G. Thirel (1), F. Regimbeau."— Presentation transcript:

1 On the importance of meteorological downscaling for short, medium and long-range hydrological ensemble prediction over France G. Thirel (1), F. Regimbeau (2), G. Tanguy (1), E. Martin (1), L. Franchisteguy (2), J.-P. Céron (2), J. Noilhan (1) and F. Habets (1) CNRM-GAME, Météo-France, CNRS, France (2) Direction de la climatologie, Météo-France, France (3) UMR-SISYPHE, ENSMP, CNRS, France +33 (0) )

2 1 model, 3 ensemblist applications (ESPS) SIM : an hydrometeorological model distributed over France Medium-range ensemble streamflow forecasts (Regimbeau et al.) –Forced by the ECMWF EPS (1.5°, 10-day range, 51 members) –Pre-alert Short-range ensemble streamflow forecasts (Thirel et al.) –Forced by the PEARP EPS (0.25°, 60-h range, 11 members) –Alert, localized and severe events Seasonal ensemble streamflow forecasts (Tanguy et al.) –Forced by DEMETER (2.5°, 4-month range, 9 members) –Water management

3 ISBA Physiographic data for soil and vegetation + MODCOU Qr Qi E H G Aquifer Daily Streamflow Surface scheme Snow SAFRAN Observations + NWP models Precipitation, temperature, humidity, wind, radiations Hydrological model Poor Weak to moderate Good Nash Habets et al. (2008) Meteorological analysis The SIM hydro-meteorological model

4 The SIM based ESPS Observations Meteor. models ANALYSIS RUN (daily) SAFRAN 10-year climatology Wind, Rad., Humidity SOIL WAT. TABLES RIVERS FINAL STATE ECMWF/PEARP/DEMETER Ensemble forecasts 51/11/9 members ENSEMBLE FORECASTS T+ Precip Spatial DISAGGREGATION ISBA MODCOU ENSEMBLE FORECAST SOIL WAT. TABLES RIVERS FINAL STATES ISBA MODCOU SOIL WAT. TABLES RIVERS STATE

5 Simple method, based on SAFRAN and an altitudinal gradient 10 October 2004 Non-perturbed run, 240h total Distance Interpolation 1/r2 ECMWF EPS Precipitations (1.5° grid) Interpolated on the SAFRAN zones Interpolated on the 8km ISBA meshes Spatial disaggregation of ECMWF EPS precipitations (Rousset-Regimbeau et al.) Altitudinal gradients T : K/100m Precip : 2 mm/m/year where altitude < 800m 0.7 mm/m/year where altitude > 800m

6 Visualization of the outputs Run every day, quasi operational Internal website updated everyday Several types of output graphs transmitted to the SCHAPI Flood risk Persistance of the flood risk

7 Spatial disaggregation of PEARP EPS precipitations (Thirel et al.) Spatial interpolation on the SAFRAN zones Altitudinal gradient : does not work! Differences not linked to relief Point by point bias removal (calibrated over a 1-year period) SAFRAN/PEARP precipitation ratio over 1 year PEARP : 0.25° grid

8 Precipitation disaggregation ECMWF : altitudinal gradient (climatological) 2 mm/m/year where altitude < 800m 0.7 mm/m/year where altitude > 800m PEARP : bias removal calibrated over one year Observations (5000 rain gauges) ECMWF (Day 1) PEARP (Day 1) Results over the test period : 10 March 2005 – 30 September 2006 Statistical scores of day 1 and 2 are better for PEARP than for ECMWF rainfall

9 Distribution by basin size (BSS against reference) Basins sizes Q10 Day 1 Q10 Day 2 Q90 Day 2 Q90 Day 1 ECMWF PEARP Basins sizes

10 Short/Mid-term ESPS conclusions 2 simple downscaling methods –A first approach, to improve! Encouraging results of ensemble streamflow forecasts SIM/PEARP improves the scores for small basins and floods –High interest for flood alert SIM/ECMWF brings useful pieces of information at a medium-range scale –Useful for water management Better PEARP and ECMWF EPS are now available –Further improvements are expected Improvement of the initial states of the ESPS by assimilation (presentation on Wednesday during the COST WG2 session)

11 Simple method as a first approach (ROUSSET-REGIMBEAU,2007) DEMETER Precipitation (2.5° grid) Interpolation on ISBA mesh - 8km Interpolation on SYMPOSIUM zones Vertical Gradient T : °K/100m Rain : to 2 mm/year/1m Interpolation 1/r² Distance Cumulated rain in mm over March- April-May 1998 SAFRAN Reference Seasonal hydrological forecasts (Tanguy et al.)

12 Soil Water Index Temporal correlation calculated against the SIM reference on March-April-May months over 31 years 1.0 High correlation for mountainous areas : good snow melting simulation (?) 0.0

13 Riverflow forecasts The Durance at Embrun : 3-month average (MAM) SIM 88 m 3 /s Means : Ensemble mean 105 m 3 /s 785 m 3 /s 758 m 3 /s Means : The Garonne at Tonneins : 3-month average (MAM) Mean riverflow in m 3 /s SAFRAN Ensemble mean Members

14 Seasonal ESPS conclusions First approach of the topic at Météo-France Better results than using the climatology Good potential to provide reliable pieces of information on soil moisture and streamflows –Water management

15 Conclusions and perspective 3 differently time/spatial-scaled ESPSs implemented at Météo-France Flood alert, pre-alert and water management can be dealt with The three systems need further work on meteorological disaggregation and model uncertainty Current PEARP and ECMWF EPS have better resolution and time-range -> improvement of ESPSs expected! PERSPECTIVES ECMWF-SIM will be in an operational mode ( ) Implementation of the assimilation system in this operational ESPS PhD Thesis to work on the seasonal forecasts (?)

16 Thank you for your attention!


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