Importance de la résolution spatiale et temporelle des approches régionales de modélisation du stress hydrique

Les pressions accrues sur les ressources en eau liées aux changements climatiques et sociétaux sont reconnues comme des enjeux mondiaux. Une approche régionale de modélisation intégrée, considérant des scénarios hydrologiques et d’usages de l’eau sous contraintes climatiques et anthropiques, a ainsi été développée. Celle-ci a d’abord été appliquée à l’échelle du bassin méditerranéen au pas de temps annuel, puis à l’échelle du canton de Vaud (Suisse) au pas de temps mensuel. Commune aux deux études, cette approche permet d’identifier les grandes tendances hydro-climatiques et d’usages de l’eau d’ici à l’horizon 2050 ainsi que les régions les plus vulnérables au stress hydrique. Ces études soulignent l’importance de pouvoir représenter les variations régionales et saisonnières de la disponibilité des ressources et des demandes en eau. S’appuyant sur les résultats de ces deux travaux, cette communication vise à discuter de la question de la résolution temporelle et spatiale des approches régionales de modélisation intégrée du stress hydrique

Consistency of satellite-based precipitation products in space and over time compared with gauge observations and snow- hydrological modelling in the Lake Titicaca region

This paper proposes a protocol to assess the space–time consistency of 12 satellite-based precipitation products (SPPs) according to various indicators, including (i) direct comparison of SPPs with 72 precipitation gauges; (ii) sensitivity of streamflow modelling to SPPs at the outlet of four basins; and (iii) the sensitivity of distributed snow models to SPPs using a MODIS snow product as reference in an unmonitored mountainous area. The protocol was applied successively to four different time windows (2000–2004, 2004–2008, 2008–2012 and 2000–2012) to account for the space–time variability of the SPPs and to a large dataset composed of 12 SPPs (CMORPH–RAW v.1, CMORPH–CRT v.1, CMORPH–BLD v.1, CHIRP v.2, CHIRPS v.2, GSMaP v.6, MSWEP v.2.1, PERSIANN, PERSIANN–CDR, TMPA–RT v.7, TMPA–Adj v.7 and SM2Rain–CCI v.2), an unprecedented comparison. The aim of using different space scales and timescales and indicators was to evaluate whether the efficiency of SPPs varies with the method of assessment, time window and location. Results revealed very high discrepancies between SPPs. Compared to precipitation gauge observations, some SPPs (CMORPH–RAW v.1, CMORPH–CRT v.1, GSMaP v.6, PERSIANN, and TMPA–RT v.7) are unable to estimate regional precipitation, whereas the others (CHIRP v.2, CHIRPS v.2, CMORPH–BLD v.1, MSWEP v.2.1, PERSIANN–CDR, and TMPA–Adj v.7) produce a realistic representation despite recurrent spatial limitation over regions with contrasted emissivity, temperature and orography. In 9 out of 10 of the cases studied, streamflow was more realistically simulated when SPPs were used as forcing precipitation data rather than precipitation derived from the available precipitation gauge networks, whereas the SPP's ability to reproduce the duration of MODIS-based snow cover resulted in poorer simulations than simulation using available precipitation gauges. Interestingly, the potential of the SPPs varied significantly when they were used to reproduce gauge precipitation estimates, streamflow observations or snow cover duration and depending on the time window considered. SPPs thus produce space–time errors that cannot be assessed when a single indicator and/or time window is used, underlining the importance of carefully considering their space–time consistency before using them for hydro-climatic studies. Among all the SPPs assessed, MSWEP v.2.1 showed the highest space–time accuracy and consistency in reproducing gauge precipitation estimates, streamflow and snow cover duration.</p

Modeling denitrification in aquatic sediments

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 93 (2009): 159-178, doi:10.1007/s10533-008-9270-z.Sediment denitrification is a major pathway of fixed nitrogen loss from aquatic systems. Due to technical difficulties in measuring this process and its spatial and temporal variability, estimates of local, regional and global denitrification have to rely on a combination of measurements and models. Here we review approaches to describing denitrification in aquatic sediments, ranging from mechanistic diagenetic models to empirical parameterizations of nitrogen fluxes across the sediment-water interface. We also present a compilation of denitrification measurements and ancillary data for different aquatic systems, ranging from freshwater to marine. Based on this data compilation we reevaluate published parameterizations of denitrification. We recommend that future models of denitrification use (1) a combination of mechanistic diagenetic models and measurements where bottom waters are temporally hypoxic or anoxic, and (2) the much simpler correlations between denitrification and sediment oxygen consumption for oxic bottom waters. For our data set, inclusion of bottom water oxygen and nitrate concentrations in a multivariate regression did not improve the statistical fit.Financial support for AEG to work on the manuscript came from NSF NSF-DEB-0423565. KF, DB and DDT acknowledge support from NOAA CHRP grant NA07NOS4780191

Patterns and dynamics of land-cover changes since the 1960s over three experimental areas in Mali

This paper addresses a critical need to provide a better quantitative Understanding of how the Sudano-Sahelian environments actually been changing under the combined impacts of climate variability and the increasing pressure of human activity Using Corona. Landsat and SPOT satellite Images of three areas (90-250 km(2)) along the climatic gradient of a large catchment in Mali, significant land-cover changes since the 1960s were identified through visual interpretation of images following a common classification scheme The pattern and trajectory of changes differed markedly between the three areas studied Over all, the 40-year trends indicate (I) in the Sahelian area, a steady increase in croplands and erosional surfaces with sparse vegetation and a corresponding drastic reduction In Woody Covers, (11) in the Sudano-Sahelian area. a large increase in croplands and a moderate reduction in woody covers, (III) III file Sudanian area. agricultural extension, deforestation, but also reforestation and land rehabilitation, Clue to alternating periods of exploitation and recolonization by natural vegetation These patterns and dynamic scan be partially explained by the differences in demographic pressure between the three areas They also highlight differences in response to anthropogenic and climate forcings depending oil the areas' respective climatic and environmental endowments. This study is a first step towards an in-depth analysis of the various forces and processes driving these changes and the formulation of prospective environmental scenarios for the catchment in line with hydrological Studies (C) 2009 Elsevier B V All rights reserve

Assessing uncertainties in climate change impacts on runoff in Western Mediterranean basins

International audienceThis paper investigates the uncertainties linked to climate change impacts on runoff in four mesoscale basins (900 to 1800 km 2) in the Mediterranean region. Runoff simulations were based on a daily conceptual model including a snow module. The model was calibrated and validated according to a differential split-sample test over a 20-year period and four competing criterions aiming to represent model structural uncertainty based on the concept of Pareto optimality. Five regional climate models (RCMs) from the Med-CORDEX initiative were used to provide temperature and precipitation projections under RCP8.5 by 2050. The RCMs' inability to realistically simulate reference climate (notably precipitation) led us to apply a monthly perturbation method in order to produce a range of climate scenarios. The structural uncertainty bounds obtained from the hydrological simulations over the reference period showed that the model was able to correctly reproduce observed runoff despite contrasted hydrological conditions in (and in between) the basins. Climate projections were shown to be convergent regarding temperatures, which could increase by about +1 to 3 • C on each basin. In contrast, no clear trends in precipitation could be put in evidence, some RCMs leading to a mean annual precipitation decrease (up to 64 %), and others to an increase (up to 33 %). The hydrological projections resulted from the combination of the hydrological simulation bounds with the range of climate projections. Despite the propagation of those uncertainties, the 2050 hydrological scenarios agreed on a significant runoff decrease (2-77 %) during spring on all basins. On the opposite, no clear trend in runoff could be observed for the other seasons

Contribution de l’enseignement de la médecine vétérinaire aux enjeux du développement durable des productions animales

This article explains the process of creating a course in veterinary medicine aimed at interesting students to the challenges of animal production. The article is a retrospective analysis of five consecutive versions of the course which resulted in the elaboration of an explicit frame of reference that links three key concepts: 1) Animal production as the object of analysis; 2) Sustainable development as the paradigm of integration of economic, social and environmental dimensions and 3) Ethical deliberation as the process of analysis. The course proposes an innovative approach based on active learning, peer-based learning and ethical deliberation to resolve the main conflict of values of a case study of a veterinary intervention from the perspective of sustainable development. The method proposed meets the requirements of the competency-based program of the Faculty of veterinary medicine on the acquisition of the competencies of professionalism and integration of the scientific approach. The pedagogical approach presented in this article contributes to the advancement of knowledge in teaching and learning of veterinary medicine by valuing knowledge and attitudes of the profession in the perspective of openness to other disciplines and interveners of the agricultural sector. This interactive method could be adapted to other post-secondary programs seeking to define the role and contribution of their discipline to different challenges linked to sustainable development.Cet article explique le processus de création d’un cours en médecine vétérinaire qui vise à intéresser les étudiants aux enjeux des productions animales. L’article est une analyse rétrospective de cinq versions successives du cours, qui a donné lieu à l’élaboration d’un cadre de référence explicite qui relie trois concepts-clés : 1) Productions animales comme objet d’analyse; 2) Développement durable comme paradigme d’intégration des dimensions économiques, sociales et environnementales et 3) Délibération éthique comme processus d’analyse. Le cours propose une approche innovatrice basée sur l’apprentissage actif, l’apprentissage par les pairs et la délibération éthique pour résoudre le principal conflit de valeurs en lien avec une étude de cas d’une intervention vétérinaire dans une perspective de développement durable. La méthode proposée répond aux exigences du programme par compétence de la Faculté de médecine vétérinaire sur l’acquisition des compétences de professionnalisme et d’intégration de la démarche scientifique. La démarche pédagogique présentée dans cet article contribue à l’avancement des connaissances en enseignement et en apprentissage de la médecine vétérinaire en valorisant les savoirs et les savoir-être de la profession dans une perspective d’ouverture aux autres disciplines et intervenants de la filière agricole. Cette méthode interactive pourrait s’adapter à d’autres programmes d’études postsecondaires cherchant à définir le rôle et la contribution de leurs disciplines à l’égard de différents défis liés au développement durable

Accounting for hydro-climatic and water use variability in the assessment of past and future water balance at the basin scale

International audienceThis study assesses water stress by 2050 in river basins facing increasing human and climatic pressures, by comparing the impacts of various combinations of possible future socio-economic and climate trends. A modelling framework integrating human and hydro-climatic dynamics and accounting for interactions between resource and demand at a 10-day time step was developed and applied in two basins of different sizes and with contrasted water uses: the Herault (2500 km2, France) and the Ebro (85 000 km2, Spain) basins. Natural streamflow was evaluated using a conceptual hydrological model (GR4j). A demand-driven reservoir management model was designed to account for streamflow regulations from the main dams. Urban water demand was estimated from time series of population and monthly unit water consumption data. Agricultural water demand was computed from time series of irrigated area, crop and soil data, and climate forcing. Indicators comparing water supply to demand at strategic resource and demand nodes were computed. This framework was successfully calibrated and validated under non-stationary human and hydro-climatic conditions over the last 40 years before being applied under four combinations of climatic and water use scenarios to differentiate the impacts of climate- and human-induced changes on streamflow and water balance. Climate simulations from the CMIP5 exercise were used to generate 18 climate scenarios at the 2050 horizon. A baseline water use scenario for 2050 was designed based on demographic and local socio-economic trends. Results showed that projected water uses are not sustainable under climate change scenarios

Modélisation des pollutions agricoles avec SWAT : application à des bassins versants de taille moyenne dans les Pays de la Loire

Nous présentons dans ce papier une utilisation du modèle agro-hydrologique semi-distribué : SWAT®. Ce modèle, interfacé avec un Système d'Information Géographique nécessite des données spatialisées et permet d'estimer les flux de polluants à l'échelle de grands bassins versants. Une première étape est de mobiliser des données appropriées (relief, pédologie, occupation des sols, pratiques agricoles, météorologie), puis de procéder à la calibration et à la validation du modèle. Il nous est ensuite possible de spatialiser les résultats de modélisation afin de constituer des indicateurs pertinents de risques et de vulnérabilité du territoire étudié. Par ailleurs, la possibilité de tests de scénarios nous semble particulièrement utile dans des démarches prospectives où les acteurs cherchent à optimiser la localisation et le choix des actions à mettre en place pour améliorer la qualité de l'eau