1. AGRHYMET DHC_CPDHC_CP Diagnostic Hydrique des Cultures CIRAD Champs Pluviométriques Crop Water Balance Calculation Using Satellite based Rainfall Estimates Using Satellite based Rainfall Estimates Presented by : Abdallah SAMBA, Agrometeorologist AGRHYMET Regional Centre at Niamey, NIGER Trieste, June 2001

2. F Introduction F Brief presentation of the geoclimatic context F Simulated water balance components F Evolution of the model F DHC_CP functionalities F Simulated results F Introduction F Brief presentation of the geoclimatic context F Simulated water balance components F Evolution of the model F DHC_CP functionalities F Simulated results OverviewOverview AGRHYMET CIRAD

3. F Need to forecast the yields of food crops in order to : best manage the cereal stocks,best manage the cereal stocks, control the fluxes andcontrol the fluxes and start in time the food aids.start in time the food aids. F Heaviness of the techniques based on the statistical investigations and polls F Using the water balance simulation to obtain parameters allowing to estimate the yields. Introduction

4. The geoclimatic Context –The sudano-sahelian belt CILSS member countriesCILSS member countries Main cropsMain crops Average annual rainfallAverage annual rainfall –Local constraints Rainfall and its interannual variabilityRainfall and its interannual variability Drought spells during the crop cycleDrought spells during the crop cycle The « Water management » approachThe « Water management » approach AGRHYMET CIRAD

5. Water fluxes and their effects on agricultural hydrosystem AgriculturalproductionAgriculturalproduction Crop transpiration Soil evaporation Drainage Precipitations Capilary rise Lixiviation Ground water Runoff ErosionErosion ( )

6. Agriculturalproduction Drainage Precipitation Ground water Simplification for Water Balance simulation (The DHC4 model ) Crop transpiration Soil evaporation

7. The Evolution of the model –Recent history 1986: the first surveys ;1986: the first surveys ; 1987-1989: the ESPACE project1987-1989: the ESPACE project (Evaluating and Monitoring Agricultural Production as related to Climate and Environnement ) (Evaluating and Monitoring Agricultural Production as related to Climate and Environnement ) –DHC4, a first approach Diagnosis toolDiagnosis tool Water balance simulationWater balance simulation Current limitationsCurrent limitations AGRHYMET CIRAD

8. DHC4 a first approach WATER BALANCE SIMULATION  File  Screen  GIS  Spreadsheet  Printer DATA BASES  PET (ATLAS)  Daily rainfall data (SUIVI)  Daily historical rainfall data (CLIMBASE) n years x stations n stations RESULTS Agrometeorological Agrometeorological Stations Stations  Available soil water  Crop  Cycle duration  Sowing date  Daily rainfall data Modem/Fax AGRHYMET CIRAD

9.  File  Screen  GIS  Spreadsheet  Printer METEOSATSatellite DATA BASES  PET  Historical rainfall data Stochastic Rainfall Generation Parameter Calibration n years x stations n stations AGRHYMET RESULTS Agrometeorological Agrometeorological Stations Stations WATER BALANCE SIMULATION Rainfall data CIRAD

10. The model functionnalities –Input data Climatic dataClimatic data – –Rainfall (satellite estimates) – –PET ( ATLASETP, 1951-1980 period) Agronomic ParametersAgronomic Parameters – –Available soil water (spatialised data) – –Crop (species and cycle duration, crop coefficients) – –Sowing dates (estimated from METEOSATimages, meteorological and field data) –Simulation results Dates of the beginning of the agricultural seasonDates of the beginning of the agricultural season Actual evapotranspirationActual evapotranspiration Water requirement satisfaction indicesWater requirement satisfaction indices Potential yields estimated 2 months before harvestPotential yields estimated 2 months before harvest –Optional Treatments Image processingImage processing Raster to Vector conversionRaster to Vector conversion AGRHYMET CIRAD

11. Calcul de l’ETR par l’algorithme d’Eagleman

12. Modeling water dynamics in the soil and root growth Sowing Rooting front Wetting front Maximumavailable water water Rootavailable Time mm of water First rain

13. Les coefficients culturaux (KCs)

14. The Simulated Water Balance Components (1) Probability of a rain event : Let Aj be the event of rain on day j and Äj the opposite event: p(A j / A j-1 ) = a11 p(A j / Ä j-1 ) = a01 Ajustment of rainfall amounts : for random rainfall generation, the repartition function is : F(x) = 1 - e -((x- x 0 )/a) its reciprocal is : F -1 (y) = x 0 - a.ln (1-y) Synthesis : we know the three parameters that caracterise a given site for a given month (a01, a11, a). We are therefore able to generate as much likely rainfall sequences as we want. Probability of a rain event : Let Aj be the event of rain on day j and Äj the opposite event: p(A j / A j-1 ) = a11 p(A j / Ä j-1 ) = a01 Ajustment of rainfall amounts : for random rainfall generation, the repartition function is : F(x) = 1 - e -((x- x 0 )/a) its reciprocal is : F -1 (y) = x 0 - a.ln (1-y) Synthesis : we know the three parameters that caracterise a given site for a given month (a01, a11, a). We are therefore able to generate as much likely rainfall sequences as we want. AGRHYMET CIRAD F The Rainfall generator : theoretical basis –Semi-random Generation probabilistic daily rainfall on a given siteprobabilistic daily rainfall on a given site Ajustement of daily rainfall to a probabilistic lawAjustement of daily rainfall to a probabilistic law –Data spatialisation –Data spatialisation using interpolation (logistic regression between stations) at a 25 km  25 km scale.

15. The Simulated Water Balance Components (2) The Eagleman relationship ETR = 0.732 - 0.05  ETM + (4.97  ETM - 0.661  ETM 2 )  HR- (8.57  ETM - 1.560  ETM 2 )  HR 2 + (4.35  ETM - 0.880  ETM 2 )  HR 3 with HR : fraction of currently available soil water relative to potential ETMp : crop maximum evapotranspiration = Kc  ETPp IRESP index IRESP % = ETR / ETM cycle  ETR / ETM  sensible the sensible phase corresponds to the flowerins-fruit set period Yield estimation RDT (kg/ha) = 11.3  IRESP -128 r   The Eagleman relationship ETR = 0.732 - 0.05  ETM + (4.97  ETM - 0.661  ETM 2 )  HR- (8.57  ETM - 1.560  ETM 2 )  HR 2 + (4.35  ETM - 0.880  ETM 2 )  HR 3 with HR : fraction of currently available soil water relative to potential ETMp : crop maximum evapotranspiration = Kc  ETPp IRESP index IRESP % = ETR / ETM cycle  ETR / ETM  sensible the sensible phase corresponds to the flowerins-fruit set period Yield estimation RDT (kg/ha) = 11.3  IRESP -128 r   AGRHYMET CIRAD F Principles of DHC_CP algorithms Calculation of daily crop water consomption using the Eagleman relationshipCalculation of daily crop water consomption using the Eagleman relationship Water satisfaction index IRESPWater satisfaction index IRESP Yield estimationYield estimation

16. DHC_CP: An Early Warning System AET: Actual EvapoTranspiration Actual evapotranspiration estimated one month before harvest harvest AGRHYMET CIRAD Potential Yield in 1994 Potential Yield Estimation

17. Suivi de la campagne agricole

19. Satisfaction des besoins en eau du mil pendant la 3ème décade d ’août 2000

20. Prévision des rendements Rendements du mil estimés au 30 Septembre 2000 dans les pays du CILSS dans les pays du CILSS

21. Prévision des rendements