Remote sensing derived evapotranspiration: comparisons to observations and models and results over the full MSG disk and selected basins

Transcription

1 4 th LSA-SAF WORKSHOP Toulouse,France, 15 th to 17 th November 2010 Remote sensing derived evapotranspiration: comparisons to observations and models and results over the full MSG disk and selected basins A. Arboleda, N. Ghilain, G. Sepulcre, F. Gellens-Meulenberghs Royal Meteorological Institute Avenue Circulaire, 3 B-1180 Brussels, Belgium

2 Layout Introduction Model description Input data Model output Validation More examples of cumulated output Further developments Concluding remarks

3 Introduction EUMETSAT SATELLITE APPLICATION FACILITIES (SAF S) LSA -SAF Land Surface Analysis OSI -SAF Ocean and Sea Ice GRAS -SAF Meteorology O3M Ozone Monitoring NWP SAF Numerical Weather Prediction CM -SAF Climate Monitoring NWC-SAF - Nowcasting and very Short Range Forecasting LSA -SAF OBJECTIVES Develop techniques to retrieve parameters related to land, land-atmosphere interactions and biospheric applications, by using data from MSG and EPS satellites Albedo (AL) Down welling Surface Short-wave Flux ( DSSF) Down welling Surface Long-wave Flux (DSLF) Evapotranspiration (MET) => DMET Land Surface Temperature (LST) Risk of Fire Mapping (RFM) Snow Cover ( SC) Surface Emissivity ( EM) Vegetation characteristics (FVC, LAI, etc)

4 Methodology MSG SEVIRI pixel Tiles: Bare soil Forest Crops Grassland ET=Evapotranspiration = evaporation + transpiration At tile level (1 α ) S + ε ( L σtsk4,i ) + H i + LEi Gi = 0 LE i = Hi = LE = Lv ET LE: ET: m-2] latent heat flux [W evapotranspiration [kg m-2 s-1] Lv ρ a [q sat (Tsk,i ) q a (Ta )] rai + rci ( ρa ra i ) [c p Gi = βi Rni (T sk, i T a ) gz a with ] βi = f ( LAI i ) Pixel value LE = ζ i LE i Evapotranspiration [mm h-1] ET = 3600 LE/Lv Lv : latent heat of vaporisation Toulouse, 15th- November 2010 LSA-SAF evapotranspiration Arboleda et al.

5 Model input AL -Surface ALbedo- from satellite MSG-II DSSF-Shortwave flux at surface DSLF-Longwave flux at surface LAI -Leaf Area Index- FVC -Fractional Vegetation Cover- LST -Land Surface Temperature- * From database (ECOCLIMAP) T i -Tiles in pixel- FV i -Fraction of tiles- Rs i -Tile minimum stomatal resistance LAI i -Tile Leaf Area Index - FVC i -Tile fractional vegetation cover AL M -Monthly pixel Albedo MODEL FORMULATION MET QF From NWP (ECMWF) Ta -Air temperature- U -Wind speed- Pa -Air pressure - Td -Dew-point temperature- ST -Soil Temperature- SM -Soil Moisture- * -To be included in future versions

6 Model output (Instantaneous) Two images are generated: the first one contains instantaneous ET estimates in mm/h while the second one is the quality flag image, provides information on the quality of estimates pixel by pixel ET [mm/h] for 2010/10/29 at 12:00 UTC Associated quality flag (-)

7 Model output (Instantaneous ET (mm/h) over full MSG disk)

8 Daily eevapotranspiration (DMET) DMET = h 2 METi ( t) dt h 1 The daily evapotranspiration product is obtained as temporal integration of instantaneous values. -MET i is the instantaneous estimate at time i -dt is time interval between 2 images (30 min) -h 1 (00:30),h 2 (24:00), the integration limits

9 Daily ET on full MSG DIISK DMET images from 06/09 to 15/ ET [mm/day] Toulouse, 15th- November 2010 LSA-SAF evapotranspiration Arboleda et al.

10 Validation Stand-alone Approaches Off-line Models inter-comparison:

11 Validation (Stand-alone) Stand-alone Validation: By comparing the output of 1-D version of the model to reference values from selected locations/stations in different regions of the world.

12 Validation (Off-line) Compare output generated by the operational (grid) version of the model to in situ observations at pre-defined locations

13 Validation (Off-line) Compare the output of the model to in situ observations

14 Validation (Off-line) Buzenol Cabauw Humain Lobos Roccarespamapni Tojal

15 Summary of off-line validation Station VegetationType * Bias RMS Corr % PRD Amplero G Buzenol G Cabauw G Humain G Monte Bondone G Tojal G Hesse DBF Roccarespampani DBF Loobos ENF Wetzstein ENF Sodankylä ENF Lonzée C Las Majadas EMF Puéchabon EMF Kaamanen B Vielsalm MF Demokeya Ss Target PRD criterion: 25 % for MET > 0.4 mm h mm h -1 for MET < 0.4 mm h -1 (Observed fluxes uncertainty: ~ 20 %) * Grassland (G), Deciduous Broadleaved Forest (DBF), Evergreen Needle Forest (ENF), Crops (C), Mixed Forest (MF), Evergreen Mediterranean Forest (EMF), Ss (Sahelian savannah)

16 Validation (Models inter-comparison) Compare the output of the ET to output from other models (NWP, GCMs, hydrological models) LSA-SAF - ECMWF LSA-SAF - GLDAS NAfr SAfr LSA-SAF - ECMWF LSA-SAF - GLDAS

17 Validation (Models inter-comparison) Cumulated (12:00 to 18:00 UTC) Evapotranspiration from LSA-SAF ET, ECMWF and GLDAS for the day

18 Validation (Models inter-comparison) Distribution of DMET (green ) and ECMWF (red) daily values between 01/09/2009 and 31/12/2009 SAfr SAme Euro NAfr

19 Validation (Models inter-comparison) Spatial correlation of daily images from DMET and ECMWF for December 2009 for: Europe (green), North Africa (red), South America (black) and South Africa(blue).

20 Validation (Models inter-comparison) Comparison with ECMWF and GLDA for the period March November 2007 at 1 degree spatial resolution MET / GLDAS MET / ECMWF

21 More examples of cumulated output (Monthly over MSG disk) May 2010 June 2010 (mm/month)

22 More examples of cumulated output (Monthly over MSG disk) Sept (mm/month) Oct. 2010

23 More examples of cumulated output (Monthly over selected hydrological basins in Africa) West Africa Basin Nile Basin South Atlantic coast Basin Congo Basin

24 More examples of cumulated output (Monthly over selected hydrological basins in Africa) Monthly Evapotranspiration over the Nile basin (May to September 2010) (mm/month)

25 More examples of cumulated output (Monthly over selected hydrological basins in Africa) Monthly Evapotranspiration over the South Atlantic coast basin ( May to September 2010) (mm/month)

26 More examples of cumulated output (Monthly over selected hydrological basins in Africa) Monthly Evapotranspiration over West Africa basin, from May to September 2010 (mm/month)

27 What is available: LAI and FVC (+ error) on pixel basis every day. What we need: LAI and FVC (+ error) for sub-pixel ecosystems. Operational constraints: final product (MET) produced in near-real time Ecoclimap Land Cover LSA-SAF LAI, FVC Further developments (On-going research) Simple methodology to get sub-pixel estimates ET model MSG grid over region LAI, FVC, z0, z0h by ecosystem Pre-processing module Mixed pixel considered for analysis Tile 2 Tile 1 Homogeneous pixel = ecosystem represents >90% of pixel. Pure ecosystems: typ 1, typ 2, typ 3 Tile 3

28 Further developments (On-going research) develop the full SVAT to account for a consistent soil moisture/temperature evolution. (H-Tessel like)

29 Evaluate the impact of using other SRS derived variables( ASCAT,LST, ) More validation in Africa / South America Further developments (On-going research) Systematic validate fluxes: LE,H, G, over pre-defined stations

30 Conclusions The LSA-SAF instantaneous and cumulated evapotranspiration products had been presented. The instantaneous product was in pre-operational status since 2009 and become operational very recently. The daily product also become operational. Comparison of the model output with ground reference data shows that model is able to reproduce the temporal evolution of evapotranspiration with values comparables to observations. From the models inter-comparison, it is concluded that ET estimates provided by the MET algorithm are equivalent to estimates provided by ECMWF and GLDAS, with spatial correlation between 85% and 95% for midday images The methodology has been validated mainly in Europe. We are interested in data from measurement campaigns and long-term measurements in other regions particularly in Africa and South America. Users feedback is expected for future improvements.

31 Acknowledgments Thanks to all validation data providers Thanks to ESA and Belgian Science Policy for co-funding this project with EUMETSAT Information about Evapotranspiration and all LSA-SAF products at: Thank you!