A new methodology is proposed for the calibration of distributed hydrological models at the basin scale by constraining an internal model variable using satellite data of land surface temperature (LST). The model algorithm solves the system of energy and mass balances in terms of a representative equilibrium temperature that governs the fluxes of energy and mass over the basin domain. This equilibrium surface temperature, which is a critical model state variable, is compared to operational satellite LST, while calibrating soil hydraulic parameters and vegetation variables differently in each pixel, minimizing the errors. This procedure is compared to the traditional calibration using only discharge measurements. The distributed energy water balance model, Flashflood Event-based Spatially-distributed rainfall-runoff Transformation -Energy Water Balance model (FEST-EWB), is used to test this approach. This methodology is applied to the Upper Yangtze River basin (China) using MODIS LST retrieved from satellite data in the framework of the NRSCC-ESA DRAGON-2 Programme. The calibration procedure based on LST seems to outperform the calibration based on discharge, with lower relative error and higher Nash-Sutcliffe efficiency index on cumulated volume.Key words energy water balance model; satellite land surface temperature; river discharge measurements Les données satellitaires de température de surface peuvent-elles être utilisées de la même manière que les mesures de débit au sol pour le calage de modèles hydrologiques distribués ?Résumé Cette étude propose une nouvelle méthodologie de calage des modèles hydrologiques distribués à l'échelle du bassin versant, en contraignant une variable interne du modèle par des données satellitaires de température de surface. L'algorithme du modèle résout le système de bilan de masse et d'énergie au niveau d'une température représentative d'équilibre, qui gouverne les flux de masse et d'énergie sur le domaine du bassin versant. Cette température de surface d'équilibre, qui est une variable d'état clé du modèle, est comparée à la température de surface fournie en routine par des satellites, en calant les paramètres hydrauliques du sol et les variables de végétation différemment dans chaque pixel par minimisation des erreurs. Cette procédure a été comparée au calage traditionnel utilisant seulement les mesures de débit. Le modèle distribué de bilan eauénergie, FEST-EWB (Flash-flood Event-based Spatially-distributed rainfall-runoff Transformation -Energy Water Balance model ; Modèle événementiel et spatialement distribué pour la transformation pluie-débit et le bilan eau-énergie lors des crues éclair) a été utilisé pour tester cette approche, appliquée au bassin amont du fleuve Yangtze, en Chine, en utilisant la température de surface MODIS obtenue à partir de données satellitaires dans le cadre du programme NRSCC-ESA DRAGON-2. La procédure de calage exploitant la température de surface semble être plus performante que le calage basé sur le débit, avec une erreur relative plus faible ...
Application of hydrological models for water resources management at large continental river basins is often limited by the scarcity of in situ meteorological forcing data. Remote sensing information provides an alternative to in situ data, with observations that are, in some cases, at higher spatial and temporal resolutions than those available from traditional ground sources. In this work, the water balance equation is solved using precipitation retrieved from Tropical Rainfall Measuring Mission, water storage from Gravity Recovery and Climate Experiment satellite data and ground discharge. Evapotranspiration (ET) is then computed as a residual term of the water balance. Satellite data are compared with ground data to understand to what extent remote sensing observations can be used to improve estimates of the terrestrial water balance at regional scale. ET estimates are also compared with the ET computed from a detailed distributed energy water balance model and with the ET product from the Moderate Resolution Imaging Spectroradiometer Global Evapotranspiration Project. These analyses are performed for the Upper Yangtze River basin (China) in the framework of NRSCC-ESA DRAGON-2 Programme.
ABSTRACT:Ten Dragon 3 projects deal with hydrologic and cryosphere processes, with a focus on the Himalayas and Qinghai -Tibet Plateau, but not limited to that. At the 1 st Dragon 3 Progress Symposium in 2013 a significant potential for a better and deeper integration appeared very clearly and we worked out an overview of the ten projects identifying specific issues and objectives shared by at least two projects. At the Mid Term Symposium in 2014 a joint session was held over two days. As regards cryospheric processes science highlights covered: Glacier flow velocity by optical and SAR features tracking and InSAR; Patterns in space and time of glacier flow velocity; Mass change estimated with DTM-s and altimetry; Reflectance and LST used to classify glacier surface and understand surface processes, Inventory and changes in the number and area of lakes in the Qinghai -Tibet Plateau 1970, 1990, 2000 and 2010; Deformation of permafrost along the Qinghai -Tibet railway. Highlights on hydrologic processes included: Global comparison of SMOS, ASCAT and ERA soil moisture data products; Relative deviations evaluated by climate zone; Soil moisture data products improved with ancillary data; Assimilation of FY -, TRMM and GPM precipitation data products in WRF; Improved algorithm and data products on fractional snow cover; Improvement of MODIS ET with assimilation of LST; TRMM data products evaluated in the Yangtze; Calibration of river basin models using LST; System to calibrate, correct and normalize (spatial, spectral) data collected by imaging spectral radiometers; Integration of data acquired by different sensors, e.g. ET Monitor with optical and microwave (SMOS, FY -3) data; Hydrological data products used both for forcing and evaluation of Qinghai -Tibet Plateau hydrological model; Wetlands vulnerability assessed through changes in land cover 1987 -2013; Multi incidence angle and multi -temporal SAR to monitor water extent. In the general session a proposal for a Dragon Water Cycle Initiative was presented.
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