Evaluation of a simple approach for crop evapotranspiration partitioning and analysis of the water budget distribution for several crop species

International audienceClimate variability and climate change induce important intra- and inter-annual variability of precipitation that significantly alters the hydrologic cycle. The surface water budgets and the plant or ecosystem water use efficiency (WUE) are in turn modified. Obtaining greater insight into how climatic variability and agricultural practices affect water budgets and regarding their components in croplands is, thus, important for adapting crop management and limiting water losses. Therefore, the principal objectives of this study are: (1) to assess the contribution of different components to the agro-ecosystem water budget and (2) to evaluate how agricultural practices and climate modify the components of the surface water budget. To achieve these goals, we tested a new method for partitioning evapotranspiration (ETR), measured by means of an eddy-covariance method, into soil evaporation (E) and plant transpiration (TR) based on marginal distribution sampling (MDS). The partitioning method proposed requires continuous flux recording and measurements of soil temperature and humidity close to the surface, global radiation above the canopy and assessment of leaf area index dynamics. This method is well suited for crops because it requires a dataset including long bare-soil periods alternating with vegetated periods for accurate partitioning estimation. We compared these estimations with calibrated simulations of the ICARE-SVAT double source mechanistic model. The results showed good agreement between the two partitioning methods, demonstrating that MDS is a convenient, simple and robust tool for estimating E with reasonable associated uncertainties. During the growing season, the proportion of E in ETR was approximately one-third and varied mainly with crop leaf area. When calculated on an annual time scale, the proportion of E in ETR reached more than 50%, depending on the crop leaf area and on the duration and distribution of bare soil within the year

Agro-hydrology and multi temporal high resolution remote sensing: toward an explicit spatial processes calibration

The recent and forthcoming availability of high resolution satellite image series offers new opportunities in agro-hydrological research and modeling. We investigated the perspective offered by improving the crop growth dynamic simulation using the distributed agro-hydrological model, Topography based Nitrogen transfer and Transforma­ tion (TNT2), using LAI map series derived from 105 Formosat-2 (F2) images during the period 2006-2010. The TNT2 model (Beaujouan et al., 2002), calibrated with dis­ charge and in-stream nitrate fluxes for the period 1985-2001, was tested on the 2006-201O dataset (climate, land use, agricultural practices, discharge and nitrate fluxes at the outlet). A priori agricultural practices obtained from an extensive field survey such as seeding date, crop cultivar,and fertilizer amount were used as input variables.Con­tinuous values of LAI as a function of cumulative daily temperature were obtained at the crop field level by fitting a double logistic equation against discrete satellite-derived LAI. Model predictions of LAI dynamics with a priori input parameters showed an temporal shift with observed LAI profiles irregularly distributed in space (between field crops) and time (between years). By re-setting seeding date at the crop field level, we proposed an optimization method to minimize efficiently this temporal shift and better fit the crop growth against the spatial observations as well as crop production. This optimization of simulated LAI has a negligible impact on water budget at the catchment scale (1 mm yr-1 in average) but a noticeable impact on in-stream nitrogen fluxes(around 12%) which is of interest considering nitrate stream contamination issues and TNT2 model objectives. This study demonstrates the contribution of forthcoming high spatial and temporal resolution products of Sentinel-2 satellite mission in improving agro-hydrological modeling by constraining the spatial representation of crop productivity

Modeling actual water use under different irrigation regimes at district scale: Application to the FAO-56 dual crop coefficient method

The modeling of irrigation in land surface models are generally based on two soil moisture parameters SMthreshold and SMtarget at which irrigation automatically starts and stops, respectively. Typically, both parameters are usually set to optimal values allowing to fill the soil water reservoir with just the estimated right amount and to avoid crop water excess at all times. The point is that agricultural practices greatly vary according to many factors (climatological, crop, soil, technical, human, etc.). To fill the gap, we propose a new calibration method of SMthreshold and SMtarget to represent the irrigation water use in any (optimal, deficit or even over) irrigation regime. The approach is tested using the dual-crop coefficient FAO-56 model implemented at the field scale over an 8100 ha irrigation district in northeastern Spain where the irrigation water use is precisely monitored at the district scale. Both irrigation parameters are first retrieved at monthly scale from the irrigation observations of year 2019. The irrigation simulated by the FAO-56 model is then evaluated against observations at district and weekly scale over 5 years (2017–2021) separately. The performance of the newly calibrated irrigation module is also assessed by comparing it against three other modules with varying configurations including default estimates for SMthreshold and SMtarget. The proposed irrigation module obtains systematically the best performance for each of the 5 years with an overall correlation coefficient of 0.95 ± 0.02 and root-mean square error of 0.27 ± 0.07 hm3/week (0.64 ± 0.17 mm/day). Unlike the three irrigation modules used as benchmark, the new irrigation module is able to reproduce the farmers’ practices throughout the year, and especially, to simulate the actual water use in the deficit and excess irrigation regimes occurring in the study area in spring and summer, respectively.This study was supported by the IDEWA project ( ANR-19-P026-003 ) of the Partnership for research and innovation in the Mediterranean area ( PRIMA ) program and by the Horizon 2020 ACCWA project (grant agreement # 823965 ) in the context of Marie Sklodowska-Curie Research and Innovation Staff Exchange (RISE) program. The authors wish to acknowledge the "Comunitat de Regants Canal Algerri Balaguer" and the Ebro Hydrographic Confederation (SAIH Ebro) for providing the observation irrigation data used in this study

Amelioration et validation du modele de fonctionnement de la végétation ISBA-A-gs: stress hydrique et flux de CO2

M. S. Chauzy Professeur, OMP-UPS, Président M. A. Chanzy Directeur de recherche, INRA Avignon, Rapporteur M. P. Ciais Chargé de recherche, LSCE Gif sur Yvette, Rapporteur M. J.-F. Soussana Directeur de recherche, INRA Clermont-Ferrand, Rapporteur M. Y. Brunet Directeur de recherche, INRA Bordeaux, Examinateur M. J.-C. Calvet Ingénieur des Ponts et Chaussées, CNRM Toulouse, ExaminateurLand surfaces schemes were developed with the aim of modelling the water and heat transfers between continental surfaces and the atmosphere. Among the components of these surfaces, the vegetation plays an important part in the dynamic of fluxes at the interface. My thesis work concerned the parameterization improvement of the surface vegetation model: ISBA-A-gs (Calvet et al, 1998). Besides solving the surface energy and water budget, this model is able to evaluate the green biomass increment of the vegetation and to estimate the leaf surface according to the climate evolution, particularly the increase of CO2 atmospheric concentration. My contribution concerned the development and the application of a water stress parameterization related to the physiological functioning of woody vegetation. I used a methodology consisting in a meta-analysis of the literature information. This methods had already been used by Calvet (2000) for herbaceous species. An application and validation work was undertaken for 3 continuous data sets from 3 European forest sites of the EUROFLUX / CarboEurope network. These data included the traditional energy budget combined with a continuous CO2 fluxes measurements. Thus and for the first time, it was possible to test the model capacity to simulate the diurnal cycle of the CO2 fluxes as well as the net annual carbon storage (Rivalland and al., 2005). Finally, I could evaluate the potentialities of a new version of the model developed by Calvet and Soussana (2001), taking into account the effect of CO2 atmospheric enrichment on the vegetation growth, associated with the soil nitrogen fertility. This model version separates the various storage compartments of the vegetation and opens prospects in modelling the complete carbon cycle and the climatic change effects on the vegetation. Along with this work, a meta-analysis and a ground experiment of nitrogen enrichment was carried out in order to determine the plasticity parameters associated with various cover types. An evaluation of the model simulations on a wheat crop was carried out by comparing the model with the INRA generic crop model STICS.Les schémas de surface ont été développés dans le but de modéliser les échanges de chaleur et d'humidité entre les surfaces continentales et l'atmosphère. Parmi les éléments constitutifs de ces surfaces, la végétation joue un rôle important dans la dynamique des flux à l'interface. Mon travail de thèse a porté sur l'amélioration de la paramétrisation de la végétation dans le modèle de surface ISBA-A-gs (Calvet et al, 1998). Ce modèle est capable de résoudre les bilans énergétique et hydrique à la surface, de calculer la croissance de la biomasse verte de la végétation, et d'estimer sa surface foliaire en tenant compte des conditions météorologiques. Ce modèle intègre également l'effet de l'augmentation de CO2 atmosphérique dans le fonctionnement de la végétation. Mon travail a porté sur l'élaboration et l'application d'une paramétrisation de l'effet du déficit hydrique sur le fonctionnement des couverts de types ligneux. Pour cela, j'ai repris une méthodologie de type méta-analyse des données de la littérature déjà utilisée par Calvet (2000) dans le cadre des couverts de types herbacés. Un travail d'application et de validation a été mené sur 3 jeux de données continues du réseau de mesure EUROFLUX / CarboEurope correspondant à 3 sites forestiers Européens. Ces données comportent les flux du bilan d'énergie classique associés à la mesure du flux de CO2. J'ai pu de ce fait, tester pour la première fois la capacité du modèle à simuler le cycle diurne du flux de CO2 ainsi qu'à estimer le stockage annuel net de carbone sur ce type de couvert (Rivalland et al., 2005). Enfin, j'ai abordé les potentialités d'une nouvelle version du modèle développée par Calvet et Soussana (2001) dont la particularité est de prendre en compte l'effet de l'enrichissement en CO2 de l'atmosphère sur la croissance de la végétation, associé à la disponibilité du milieu en azote du sol. Cette version sépare les différents compartiments de stockage liés à la croissance de la végétation et ouvre des perspectives dans la modélisation complète du cycle du carbone et des effets du changement climatique sur la végétation. En lien avec ce travail, une méta-analyse ainsi qu'une expérimentation de terrain de fertilisation en azote a été menée dans le but de déterminer les paramètres de plasticité propres à cette version, pour différents types de couverts. Une évaluation des simulations du modèle sur une culture de blé a été menée en comparant avec le modèle de culture STICS de l'INRA

Amélioration et validation du modèle de fonctionnement de la végétation ISBA-A-gs (stress hydrique et flux de CO2)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Table ronde : « Éditer l\u27imaginaire aujourd\u27hui »

Cette table ronde réunit trois éditeurs spécialistes des genres de l\u27imaginaire pour interroger la spécificité de leur production éditoriale. Hania Jalk (éditions Bragelonne), Mireille Rivalland (Atalante) et Jérôme Vincent (Actu SF) replacent les littératures de l\u27imaginaire dans l\u27espace et le temps, en explorant les particularités de l\u27édition française, puis en tentant d\u27anticiper l\u27avenir de leur profession. Le débat s\u27orienter ensuite vers le modèle économique qui sous-tend l\u27édition de l\u27imaginaire, comparée à l\u27édition traditionnelle, puis vers les évolutions dues à l\u27arrivée du numérique et d\u27Internet. La réflexion collective s\u27achève sur des produits éditoriaux autres que le livre, mais très présents au sein des mondes de l\u27imaginaire, tels les jeux vidéos, la bande dessinée ou le cinéma

Assessing the usefulness of Land Surface Temperature spatial disaggregation for water stress mapping in the frame of the preparation of the Trishna mission

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6 years time-series of estimation and validation of land surface temperature from Landsat 5 & 7 archive on 3 plots of south-west of France

International audienc

Assessing the usefulness of Land Surface Temperature spatial disaggregation for water stress mapping in the frame of the preparation of the Trishna mission

International audienc

Assessing the usefulness of Land Surface Temperature spatial disaggregation for water stress mapping in the frame of the preparation of the Trishna mission

International audienc