-Corbari C, Ravazzani G, Mancini M. A distributed thermodynamic model for energy and mass balance computation: FEST-EWB. Hydrol. Process. 2011; 25: 1443–1452. -Corbari, C., Mancini, M. (2014), Calibration and validation of a distributed energy water balance model using satellite data of land surface temperature and ground discharge measurements, Journal of hydrometeorology, 15, 376-392 Chiara Corbari , Marco Mancini Politecnico di Milano, Milano, Italy [email protected] , www.FEST.POLIMI.it Calibration and validation of distributed models at basin scale generally refer to external variables, which are integrated catchment model outputs, and usually depend on the comparison between simulated and observed discharges at the available rivers cross sections, which are usually very few. However distributed models allow an internal validation due to their intrinsic structure, so that internal processes and variables of the model can be controlled in each cell of the domain. In particular this work investigates the potentiality to control evapotranspiration and its spatial and temporal variability through the detection of land surface temperature (LST) from satellite remote sensing. This study proposes a methodology for the calibration of distributed hydrological models at basin scale using remote sensing data of land surface temperature. The distributed energy water balance model, Flash–flood Event–based Spatially–distributed rainfall–runoff Transformation - Energy Water Balance model (FEST-EWB) will be calibrated in the Upper Po river basin (Italy) closed at the river cross section of Ponte della Becca with a total catchment area of about 38000 km2. The model algorithm solves the system of energy and mass balances in term of the representative pixel equilibrium temperature (RET) that governs the fluxes of energy and mass over the basin domain. This equilibrium surface temperature, which is a critical model state variable, is comparable to the land surface temperature (LST) from satellite. So a pixel to pixel semi-automatic calibration procedure of soil and vegetation parameter is presented through the comparison between the model internal state variable RET and the remotely observed LST. A similar calibration procedure will also be applied performing the traditional calibration using only discharge measurements. 130 diurnal and nocturne LST MODIS products are compared with FEST-EWB land surface temperature over the 4 years of simulation from 2000 to 2003 where meteorological and hydrological ground data are available. ABSTRACT Soil water balance Energy balance FEST-EWB model solves the system of energy and mass balances in term of a representative equilibrium temperature (RET) that governs the fluxes of energy and mass FEST-EWB: F lash – flood E vent – based S patially – distributed rainfall – runoff T ransformation – including E nergy - W ater B alance Distributed hydrological model calibration through satellite land surface temperature and discharge data DEM Soil Parameters Vegeta2on Parameters Snow Dynamics Spa2al interpola2on: Thiessen, IDW Defini2on of river network Subsurface rou2ng Surface flow rou2ng Hydrograph Percola2on Surface Runoff Input Output LEGEND Process Internal variable ground water Lakes and reservoires LST SM Energy fluxes Meteorological data S 0 S d S t αS t L 0 L i Λ E H 25 July 9:30 UTC AIRBORNE LST AHS Δx= 5 m °C 3 km 3 km HETEROGENEUS AREA: 65% of cultivated lands at Barrax are dryland (67% winter cereals, 33% fallow) and 35% irrigated land (75% corn, 15% barley/sunflower, 5% alfalfa, 5% onions and other vegetables). Soil paramters are calibrated minimizing the difference between observed and simulated LST EC1: camelina EC2: vineyard EC3: reforestation before calibration After calibration MAE (%) MD(AHS - FEST- EWB) (°C) MAD (°C) RMSD MAE (%) MD(AHS - FEST-EWB) (°C) MAD RMSD 9.5 0.7 3.4 4.6 3.4 -0.9 1.5 2.1 RET FEST-EWB_not calibrated RET FEST-EWB calibrated ...with different configurations… Energy budget closure 82 % (Van der Tol et al., 2015) not calibrated calibrated MAD (W m -2 ) MAE (%) MAD (W m -2 ) MAE (%) Rn 20 3.5 10 3 G 180 55 98 26 H 50 26 33 13 LE 100 70 12 17 H e LE are compared considering eddy covariance footprint (Hisie et al. 2000; Corbari et al., 2015) 25 July 9:30 UTC ENERGY FLUXES LOCAL VALIDATION CONCLUSIONS Solving the energy budget on land surface temperature allows to use this variable as internal control of hydrologic simulations. It can be promising tool to calibrate the soil and vegetation parameters of the distributed water balance model complementary to the traditional comparison based on discharge measurements. TOCE BORMIDA MAGGI A SESIA TICINO ORBA BELBO STURA DI DEMONTE PO SCRIVIA TANARO MAGGIO RE LAKE PADDIES Toce at Candoglia CALIBRATION: comparison among FEST-EWB & MODIS LST 6000 N pixels 3000 MODIS FEST-EWB 1- originali 2-ksat modified ( °C ) LST 3-ksat, depth 4-ksat, depth, bc, rs min + - RET (° C) Pixel base calibratiob 2000 – 2003, 130 MODIS LST images with cloud coverage percentage less then 30% Mean absolute difference 1.8 °C, RMSE 3.4 °C Mean average over pixels of the absolute difference between RET and LST- MODIS Autocorrelation function 6 july 2000 13:00 Volume Error (calibrated Q) = 3.2 % Volume Error (calibrated LST+Q) = -0.14 % Nash (calibrated Q) = 0.90 Nash (calibrated LST+Q) = 0.87 J. Dooge( 1986) observing internal state variables of hydrologic model ( θ) TradiNonal calibraNon on point measurements (observed discharge,local soil moisture or evapotranspiraNon) calibrated Not calibrated Each pixel is mul.plied by a local factor which depends on the temperature matrix differences Soil parameters: same spa.al distribu.on FESTEWB MODIS calibrated Not calibrated SUPERFICIAL Soil parameters: Increased spaNal variability !T (.) = Min ( RET (.) " LST (.)) !Q = Min (Qobs "Qsim) Each pixel is mul.plied by a common factor which depends on discharge differences Hydrological model calibraNon with distributed informaNon: satellite images of land surface temperature (LST) Is it reasonable to use evaporaNon flux “measures” similarly to discharge measurements? PIXEL to PIXEL calibraNon on satellite LST Basin scale: UPPER PO river basin (Italy) Agricultural scale: Barrax (2012 experiment) Laboratory scale: lysimeter DIMENSIONS Length, width =1.5 m height =1.0 m Weight = 956 kg without soil Weight about 4700 kg with soil PIXEL BY PIXEL CALIBRATION BY COMPARING AIRBORNE AND FEST-EWB LST The energy water balance hydrological model calibration Calibration of soil paramters regulating surface processes Calibration of soil paramters regulating sub-surface processes CALIBRATION: comparison among FEST-EWB & ground discharge Before calibration Combined LST and Q calibration leads to good agreement with observed discharge (volume) and also SM (evapotranspiration) better spatial distribution measured Fully equipped to measure all the process of the hydrological cycle FEST-EWB model