on the importance of meteorological downscaling for short, medium and long-range hydrological...
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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 (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
(guillaume.thirel@meteo.fr, +33 (0) 5 61 07 97 30)
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
ISBA
Physiographic data for soil and vegetation
+
MODCOU
QrQi
E
H
G
Aquifer
DailyStreamflow
Surface scheme
Snow
SAFRANObservations + NWP modelsPrecipitation, temperature, humidity, wind, radiations
Hydrological modelPoor
Weak to moderate
Good
Nash
Habets et al. (2008)
Meteorological analysis
The SIM hydro-meteorological model
The SIM based ESPS
ObservationsMeteor. models
ANALYSIS RUN (daily)
SAFRAN10-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
• 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 gradientsT : -0.65 K/100mPrecip : • 2 mm/m/year where altitude < 800m • 0.7 mm/m/year where altitude > 800m
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
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
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
Distribution by basin size (BSS against reference)
Basins sizes
Q10 Day 1
Q10 Day 2
Q90 Day 2
Q90 Day 1
ECMWF
PEARPBasins sizesBasins sizes
Basins sizes
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 statesof the ESPS by assimilation(presentation on Wednesday during the COST WG2 session)
Simple method as a first approach (ROUSSET-REGIMBEAU,2007)
DEMETER Precipitation (2.5° grid)
Interpolation on ISBA mesh - 8km
Interpolation on SYMPOSIUM zones
Vertical GradientT : -0.65 °K/100m
Rain : + 0.7 to 2 mm/year/1m
Interpolation1/r²
Distance
Cumulated rain in mm over March-April-May 1998
SAFRANReference
Seasonal hydrological forecasts (Tanguy et al.)
Soil Water Index
Temporal correlation calculated against the SIM reference on March-April-May months over 31 years
1.0
-1.0
High correlation for mountainous areas : good snow melting simulation (?)
0.0
Riverflow forecasts The Durance at Embrun : 3-month
average (MAM)
SIM 88 m3/sMeans :
Ensemble mean 105 m3/s
785 m3/s
758 m3/s
Means :
The Garonne at Tonneins : 3-month
average (MAM)
Mean riverflow in m3 /s
SAFRAN Ensemble mean Members
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
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 (2010-2011) Implementation of the assimilation system in this operational ESPS PhD Thesis to work on the seasonal forecasts (?)
Thank you for your attention!
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