Malgré le déficit pluviométrique persistant qui le caractérise depuis plus de quarante ans, le Sahel connaît un accroissement notoire du ruissellement, des écoulements et de l'érosion hydrique. On attribue cela aux changements d'usage des sols, et à une fatigue de ceux-ci, épuisés par des successions de cultures de moins en moins suivies de phases de repos. Cela se traduit par une dégradation rapide des sols, dont le processus le plus courant est l'encroûtement. C'est ce même encroûtement qui est à l'origine de l'augmentation des écoulements. On se propose ici de déterminer quelle est l'évolution de l'occupation des sols dans une région de l'Ouest du Niger, afin de comprendre les facteurs et les processus qui aboutissent à de très nettes modifications dans le régime des eaux ; outre l'augmentation des débits et des coefficients d'écoulement, on observe une diminution des temps de réponse des sols et des bassins aux précipitations. Ceci est directement lié à la diminution de la capacité des sols à retenir l'eau, qui est elle-même due à l'encroûtement. L'évolution de l'occupation des sols est donc l'explication qui permet de comprendre les modifications du cycle de l'eau. On utilise ici la télédétection pour parvenir à déterminer cette évolution des usages des sols. Au passage, on essaie d'y voir plus clair sur le reverdissement observé et mesuré par de nombreux chercheurs : est- il tangible ? Dans quelles régions ? Sur quelles durées ? Quel est le rôle des méthodes de classification dans la mise en évidence de ce reverdissement ? Il faut aussi s'assurer de la représentativité des zones d'entraînement utilisées. Des méthodes de l'hydro-géomorphométrie sont appelées au secours pour séparer la zone d'étude en deux ensembles distincts (plateau- non plateau) pour faciliter la classification. Une étude par photo-interprétation est tentée sur le degré carré de Niamey, dans l'optique d'avancer dans la distinction du rôle respectif de la sécheresse et des activités socio-économiques dans les changements d'usage des sols. Enfin, après avoir comparé nos travaux avec les très nombreuses études déjà réalisées dans cette région, on s'intéresse à l'impact des changements d'usage des sols sur l'infiltration et le ruissellement, de l'échelle de la parcelle à celle du grand bassin versant, en particulier sur l'évolution remarquée des débits et régimes des fleuves, et de l'accroissement du risque de crue, observé ces dernières années. Il semblerait que 2 à 5% de surface de sol encroûté sur un bassin suffise à accroître et concentrer suffisamment les débits pour accroître cet aléa, sans pour autant empêcher un certain « reverdissement » global, tel qu'observé par l'évolution des indices de végétation télédétectés. / Despite the persistent rainfall deficit observed from more than forty years, the West African Sahel exhibits a significant increase in runoff, in rivers discharge and in water erosion. This fact is attributed to land use changes, particularly to soil overexploitation, characterized by the shortening of fallow periods. This leads to the degradation of soil structure, and to soil crusting. The soil crusting is the first factor of the increase in runoff. The purpose of this research is to determine the land use evolution in the western part of the Niger, to underline the factors and processes leading to the significant changes in surface water regime. The increase in discharges and runoff coefficients is accompanied with a reduction in the lag time of the slopes and basins when occurs a rainy event. This is directly linked to the decrease in soil water holding capacity, due to soil crusting. Hence, land use/land cover evolution is the main explaining factor of water cycle changes. Remote sensing is used in order to determine land uses changes. This implies to improve the knowledge about the “regreening” of the Sahel, observed and measured by several research teams: is it a myth or a reality? In what regions? During what periods? What is the role of classification methods of remote sensing in the highlighting of the regreening? We need to ensure that regions of interest used in this study are representative of the regional area. Methods of “hydro-geomorphometry” are needed to divide the study area into two differents areas, “plateau” and “non-plateau”, in order to avoid errors in the pixel classification of some different vegetation types which have neighbouring NDVI. A study by interpretation of aerial photographs is attempted over the Square degree of Niamey, with the aim of improving the separation between the respective role of the drought and the human activities in the evolution of land cover. After a comparison of our research with numerous previous studies realised on the same region, we perform an analyse of the impact of land use changes on infiltration and runoff, from the plot scale to the great basin scale, with a special focus on the observed evolution of rivers discharges and regimes and on the increase in flood hazard, detected during the last years. It appears that 2 to 5% of the total area exhibiting soil crusting are sufficient to increase and concentrate enough the discharges and to provoke a significant rise in the flooding, without avoiding a certain global “regreening” such as it is observed using the evolution of vegetation indices.

O presente trabalho investiga a construção de abordagens centradas em temas, dirigidas ao ensino médio, tomando como exemplo a temática da água. A escolha do tema tem sua justificativa apoiada na ampla abordagem que ele proporciona, desde questões ambientais e socioeconômicas, até as possibilidades de revitalizar o potencial da escola em gerar participação. Para a construção da proposta analisamos, inicialmente, dois aspectos que contextualizam um espaço de intervenção, caracterizando, por um lado, a estrutura curricular em que o tema pode ser inserido, a partir da análise de livros didáticos e, por outro, algumas idéias de alunos sobre a questão. Em particular, investigamos a articulação entre os aspectos dos temas tratados e os conceitos físicos a serem construídos. Nesse sentido, propomos a construção de representações de duas naturezas diferentes, denominadas de organização temática e organização conceitual, que, em conjunto, representam o âmbito das escolhas dos percursos temáticos a serem construídos pelos alunos e professores. Como exemplo, desenvolvemos três percursos temáticos, considerando como ponto de partida a questão de uma eventual escassez futura de água e representações do ciclo da água. Analisamos, ainda, o sentido da introdução de uma abordagem complexa para as questões das águas, buscando investigar em que consiste tal abordagem. Dessa forma, além de aprofundar a temática da água, propomos elementos que podem servir de ponto de partida para a construção de propostas temáticas e novas investigações. / The present work investigates the design of thematic approaches to be developed in science classes at High School level. It takes as an example questions and aspects related to the water thematic. The choice is justified by the wide range of possibilities that it provides, including environmental as well as social and economic aspects. In addition, it allows students involvement on social meaningful questions. To a first approximation, it is proposed a characterization of the intervention background conditions, by investigating the curriculum structure in that the theme can be inserted, using for that textbook analyzes. In this same direction, students´ ideas on the subject are also important sources and must be considered. For the designing of the approach, it is proposed the identification and construction of two different conceptual network structures, one referred to thematic organization and the other to physical concepts organization. These structures together represent the ambit of the choices about what teachers and students can decide to study. Each proposition of study or course means a specific interrelation of elements from these two structures, a specific itinerary to be built. As examples, three thematic paths are presented, all considering the question of an eventual future shortage of water and representations of the water cycle. In these examples, it is also analyzed the meaning of introducing complexity approaches, trying to identify its implication. With these contributions, this work pretends to have recognized some meaningful elements to be considered in the design of thematic instructions and also aspects that need to be better investigated about the subject.

Le modèle de climat global martien (GCM) du Laboratoire de Météorologie Dynamique est appliqué à l'étude du cycle de l'eau de la planète rouge. Les observations disponibles sont comparées aux simulations pour comprendre les phénomènes physiques influençant le cycle, en se focalisant sur les nuages et la vapeur d'eau. De nouvelles inversions de données de vapeur d'eau sont présentées, pour compléter notre connaissance du cycle et de sa variabilité interannuelle. De telles intercomparaisons ont des limites qu'il faut mettre en évidence pour mieux les surmonter. Les observations contraignent l'épaisseur et l'étendue des nuages ainsi que leur chronologie saisonnière. Pour améliorer la représentation du cycle de l'eau, la piste de la simulation à haute résolution est explorée, avec des simulations de un degré en résolution horizontale. Des phénomènes nouveaux émergent, comme des tempêtes en spirale. Des changements visibles affectent le cycle de l'eau, avec des transitions ondulatoires, des instabilités renforcées, une modification du dépôt de givre et une meilleure représentation du cycle de condensation et sublimation. La circulation est intensifiée, tout comme la variabilité du cycle, et l'on découvre une atmosphère plus humide, nuageuse et changeante. Suite aux découvertes de la haute résolution, on cherche à mieux représenter la couverture nuageuse dans le modèle à résolution standard. La nouvelle paramétrisation de la couverture nuageuse partielle sous maille est décrite et ses conséquences sur le cycle de l'eau analysées. Elle est prometteuse pour améliorer le réalisme du modèle mais semble déstabiliser le cycle. / The global climate model (GCM) of the Laboratoire de Météorologie Dynamique is used to study the Martian water cycle. Available observations are compared to simulations to unravel the physical phenomena affecting the cycle, with a focus on clouds and water vapor. New inversions of water vapor observations are described and analyzed, to further our understanding of the cycle and of its interannual variability. Such comparisons are limited by bias that have to be studied. Observations constrain the timing, thickness and cover of the clouds. To improve the water cycle simulation and understanding, new high-resolution simulations with an horizontal resolution of one degree are shown. New phenomena appear, like spiral storms. The water cycle undergoes visible changes, with wave transitions, strengthened instabilities, shifts in frost deposition and a better simulation of the condensation and sublimation seasonal processes. The circulation is strengthened, as is variability. The atmosphere is wetter, more cloudy and more variable. Following the details discovered in the high-resolution simulations, we try to improve the representation of cloud cover in the standard resolution simulations. The subsequent new subgrid-scale parametrization of partial cloudiness is described, and its consequences on the water cycle are analyzed. Results are promising as the model agrees more with observations in some ways, but the parametrization causes further instability.

Iodine-129 is a naturally and anthropogenically produced radioisotope (half-life: 15.7 million years) the majority of which is produced by nuclear fuel reprocessing. These releases have dispersed 129I throughout the environment making it possible to use 129I as a tracer. It is also of concern for the disposal of radioactive waste. This research develops a new laboratory method for 129I extraction and analysis, and explores the geochemical cycling and environmental fate of 129I in remote catchments following the Fukushima-Daiichi Nuclear Accident (FDNA). A new technique was developed to investigate 129I partitioning and quantitatively extract it from solid samples. Samples are combusted and volatilized iodine is trapped in solution. The efficiency is traced using the iodine isotope, 125I. This technique was proven using standard reference materials and is used in other chapters of this thesis. A baseline study of 129I in Yukon watersheds was undertaken to determine the impact of anthropogenic 129I emissions and identify possible sources. Using atmospheric back-trajectory modeling, sources of 129I from Fukushima, nuclear fuel reprocessing and marine volatilization were identified in remote watersheds. Peat moss samples showed significant retention of 129I in modern samples. Following the reconnaissance study, a catchment scale investigation of anthropogenic 129I cycling was undertaken through precipitation and runoff monitoring. 129I was found to be an excellent indicator of initial snowmelt contributions to discharge due to enrichment by dry deposition. Furthermore, water source transitions in discharge were recorded by 129I, 127I and the 129I/127I ratio showing iodine can be used as a tracer of hydrologic processes. A mass balance found that 77% of the 129I mass input accumulates annually, primarily in organic soils. Sampling of Vancouver, B.C. precipitation and groundwater was done following the FDNA to determine the fate of 129I and evaluate it as a tracer of groundwater recharge. Immediately following the FDNA the 129I concentration in precipitation increased 6 times above background. Groundwater samples also showed 129I increases consistent with expected recharge times indicating FDNA derived 129I was transported into groundwater with minimal retardation, likely via preferential flowpaths.

Numerische Experimente wurden durchgeführt, um den Einfluß von Gittermaschenweite und subskaliger Heterogenität auf die Vorhersage der am Wasserkreislauf beteiligten Größen zu untersuchen. Die Modellergebnisse zeigen, daß die Evapotranspiration, Bewölkung und der Niederschlag von der Gittermaschenweite und der Heterogenität beeinflußt werden. Es zeigte sich, daß bei Verwendung gröberer Maschenweiten unter Einbezug der verschiedenen Landnutzungstypen innerhalb der Gittermasche die Obertlächenprozesse und Phänomene (z.B. Wärmeinseleffekt) realistischer beschrieben werden, als wenn nur ein Landnutzungstyp für das gesamte Gitterelement angenommen wird. / Numerical experiments were performed to investigate the influence of grid resolution and subgrid heterogeneity on the prediction of the quantities of the water cycle. The results were compared with each other and with those provided by a simulation using the same surface parameterization scheme but taking subgrid scale surface heterogeneity into account. The model results substantiate that the evapotranspiration, cloudiness and precipitation are affected by the grid resolution and the heterogeneity. lt was found that increasing the grid size but including the heterogeneity describes more realistically the surface processes and phenomena (e.g„ heat island effect) than assuming one land use type for the whole grid element.

A land-surface module to couple a meteorological and a hydrologic model is described. lt was implemented and tested in the Leipzig\''s version of GESIMA. Preliminary results of a coupling with NASMO are presented, although this article mainly focuses on the description of the module and its effect on the atmospheric water cycle. One positive impact of the module is that it allows to produce subgrid-scale evapotranspiration in more details and to heterogenize precipitation. This strongly affects soil wetness, cloudiness and the thermal regime of the atmospheric boundary layer. / Ein Bodenmodul zur Kopplung eines meteorologischen mit einem hydrologischen Modell wird vorgestellt. Er wurde implementiert und getestet in der Leipziger Version von GESIMA. Obgleich der Schwerpunkt des Artikels auf der Beschreibung des Moduls und seiner Auswirkung auf den atmosphärischen Wasserkreislauf liegt, werden auch vorläufige Ergebnisse einer Kopplung mit NASMO präsentiert. Ein positiver Effekt des Moduls ist, daß er ermöglicht, detaillierter die subskalige Evapotranspiration zu beschreiben und den Niederschlag zu heterogenisieren. Dies wirkt sich stark auf die Bodenfeuchte, die Bewölkung und das thermische Regime der atmosphärischen Grenzschicht aus.

No description available.

Reliability of water supply in the urban setting has become essential for communities to function and thrive. It is needed for more than mere human consumption and well-being. Although modern cities have water treatment and distribution systems, pressures from urbanization, population growth and the anticipated pressures of climate change are affecting the quality of water supply and the reliability of treatment and distribution systems. There is therefore an urgent need to take appropriate measures to improve the resilience of water supply systems before the impacts are irreversible. Improving the resilience of water supply systems can be a challenge. In the United States, there is increased awareness of aging, overtaxed and under designed water infrastructure. To date, resilience planning has been principally focused on improving preparedness and the restoration of critical services in communities following extreme events, such as hurricanes, earthquakes or terrorism, and less so on the slow-moving consequences of climate change, perceived as a less urgent threat. All these issues – increased pressure of urbanization and population growth, deteriorating infrastructure, together with the consequences the impacts of climate change may have on water systems and the apathetic view of the need for action – are what make the development of a solution difficult. This research proposes Integrated Urban Water Management as a new water management paradigm as one that can withstand contemporary issues as well as future climate threats, while increasing water supply resilience for communities. This research (1) focuses on analyzing the urban water cycle for potential vulnerabilities, (2) seeks to understand the benefits and challenges of integrating water infrastructure, (3) tests the level of sustainability in an IUWM system, (4) identifies critical thresholds ‘slow-moving’ climate change on water supply infrastructure, (5) performs a system-wide water and salt balance and (6) tests the system for resilience to salt water intrusion. Since coastal communities are subject to higher population densities, demands on resources, and exposed to greater threats than inland communities, this project utilizes a coastal community with integrated water infrastructure as a basis to better understand the benefits as well as the potential challenges of the proposed future paradigm (IUWM). The results of this research show that IUWM offers many options for sustainable practices as well as adaptability, a key aspect of resilience. The conclusions drawn from the scoping study, case study and modeling of water and salt flows within the urban water cycle offer relevant and transferable lessons for water management in coastal cities while they approach uncertain and alternative climate futures.

Since the start-up of the GRACE (Gravity Recovery And Climate Experiment) mission in 2002 time dependent global maps of the Earth's gravity field are available to study geophysical and climatologically-driven mass redistributions on the Earth's surface. In particular, GRACE observations of total water storage changes (TWSV) provide a comprehensive data set for analysing the water cycle on large scales. Therefore they are invaluable for validation and calibration of large-scale hydrological models as the WaterGAP Global Hydrology Model (WGHM) which simulates the continental water cycle including its most important components, such as soil, snow, canopy, surface- and groundwater. Hitherto, WGHM exhibits significant differences to GRACE, especially for the seasonal amplitude of TWSV. The need for a validation of hydrological models is further highlighted by large differences between several global models, e.g. WGHM, the Global Land Data Assimilation System (GLDAS) and the Land Dynamics model (LaD). For this purpose, GRACE links geodetic and hydrological research aspects. This link demands the development of adequate data integration methods on both sides, forming the main objectives of this work. They include the derivation of accurate GRACE-based water storage changes, the development of strategies to integrate GRACE data into a global hydrological model as well as a calibration method, followed by the re-calibration of WGHM in order to analyse process and model responses. To achieve these aims, GRACE filter tools for the derivation of regionally averaged TWSV were evaluated for specific river basins. Here, a decorrelation filter using GRACE orbits for its design is most efficient among the tested methods. Consistency in data and equal spatial resolution between observed and simulated TWSV were realised by the inclusion of all most important hydrological processes and an equal filtering of both data sets. Appropriate calibration parameters were derived by a WGHM sensitivity analysis against TWSV. Finally, a multi-objective calibration framework was developed to constrain model predictions by both river discharge and GRACE TWSV, realised with a respective evolutionary method, the ε-Non-dominated-Sorting-Genetic-Algorithm-II (ε-NSGAII). Model calibration was done for the 28 largest river basins worldwide and for most of them improved simulation results were achieved with regard to both objectives. From the multi-objective approach more reliable and consistent simulations of TWSV within the continental water cycle were gained and possible model structure errors or mis-modelled processes for specific river basins detected. For tropical regions as such, the seasonal amplitude of water mass variations has increased. The findings lead to an improved understanding of hydrological processes and their representation in the global model. Finally, the robustness of the results is analysed with respect to GRACE and runoff measurement errors. As a main conclusion obtained from the results, not only soil water and snow storage but also groundwater and surface water storage have to be included in the comparison of the modelled and GRACE-derived total water budged data. Regarding model calibration, the regional varying distribution of parameter sensitivity suggests to tune only parameter of important processes within each region. Furthermore, observations of single storage components beside runoff are necessary to improve signal amplitudes and timing of simulated TWSV as well as to evaluate them with higher accuracy. The results of this work highlight the valuable nature of GRACE data when merged into large-scale hydrological modelling and depict methods to improve large-scale hydrological models. / Das Schwerefeld der Erde spiegelt die Verteilung von Massen auf und unter der Erdoberfläche wieder. Umverteilungen von Erd-, Luft- oder Wassermassen auf unserem Planeten sind damit über eine kontinuierliche Vermessung des Erdschwerefeldes beobachtbar. Besonders Satellitenmissionen sind hierfür geeignet, da deren Umlaufbahn durch zeitliche und räumliche Veränderung der Schwerkraft beeinflusst wird. Seit dem Start der Satellitenmission GRACE (Gravity Recovery And Climate Experiment) im Jahr 2002 stellt die Geodäsie daher globale Daten von zeitlichen Veränderungen des Erdschwerefeldes mit hoher Genauigkeit zur Verfügung. Mit diesen Daten lassen sich geophysikalische und klimatologische Massenumverteilungen auf der Erdoberfläche studieren. GRACE liefert damit erstmals Beobachtungen von Variationen des gesamten kontinentalen Wasserspeichers, welche außerordentlich wertvoll für die Analyse des Wasserkreislaufes über große Regionen sind. Die Daten ermöglichen die Überprüfung von großräumigen mathematischen Modellen der Hydrologie, welche den natürlichen Kreislauf des Wassers auf den Kontinenten, vom Zeitpunkt des Niederschlags bis zum Abfluss in die Ozeane, nachvollziehbar machen. Das verbesserte Verständnis über Transport- und Speicherprozesse von Süßwasser ist für genauere Vorhersagen über zukünftige Wasserverfügbarkeit oder potentielle Naturkatastrophen, wie z.B. Überschwemmungen, von enormer Bedeutung. Ein globales Modell, welches die wichtigsten Komponenten des Wasserkreislaufes (Boden, Schnee, Interzeption, Oberflächen- und Grundwasser) berechnet, ist das "WaterGAP Global Hydrology Model" (WGHM). Vergleiche von berechneten und beobachteten Wassermassenvariationen weisen bisher insbesondere in der jährlichen Amplitude deutliche Differenzen auf. Sehr große Unterschiede zwischen verschiedenen hydrologischen Modellen betonen die Notwendigkeit, deren Berechnungen zu verbessern. Zu diesem Zweck verbindet GRACE die Wissenschaftsbereiche der Geodäsie und der Hydrologie. Diese Verknüpfung verlangt von beiden Seiten die Entwicklung geeigneter Methoden zur Datenintegration, welche die Hauptaufgaben dieser Arbeit darstellten. Dabei handelt es sich insbesondere um die Auswertung der GRACE-Daten mit möglichst hoher Genauigkeit sowie um die Entwicklung einer Strategie zur Integration von GRACE Daten in das hydrologische Modell. Mit Hilfe von GRACE wurde das Modell neu kalbriert, d.h. Parameter im Modell so verändert, dass die hydrologischen Berechnungen besser mit den GRACE Beobachtungen übereinstimmen. Dabei kam ein multikriterieller Kalibrieralgorithmus zur Anwendung mit dem neben GRACE-Daten auch Abflussmessungen einbezogen werden konnten. Die Modellkalibierung wurde weltweit für die 28 größten Flusseinzugsgebiete durchgeführt. In den meisten Fällen konnte eine verbesserte Berechnung von Wassermassenvariationen und Abflüssen erreicht werden. Hieraus ergeben sich, z.B. für tropische Regionen, größere saisonale Variationen. Die Ergebnisse führen zu einem verbesserten Verständnis hydrologischer Prozesse. Zum Schluss konnte die Robustheit der Ergebnisse gegenüber Fehlern in GRACE- und Abflussmessungen erfolgreich getestet werden. Nach den wichtigsten Schlussfolgerungen, die aus den Ergebnissen abgeleitet werden konnten, sind nicht nur Bodenfeuchte- und Schneespeicher, sondern auch Grundwasser- und Oberflächenwasserspeicher in Vergleiche von berechneten und GRACE-beobachteten Wassermassenvariationen einzubeziehen. Weiterhin sind neben Abflussmessungen zusätzlich Beobachtungen von weiteren hydrologischen Prozessen notwendig, um die Ergebnisse mit größerer Genauigkeit überprüfen zu können. Die Ergebnisse dieser Arbeit heben hervor, wie wertvoll GRACE-Daten für die großräumige Hydrologie sind und eröffnen eine Methode zur Verbesserung unseres Verständnisses des globalen Wasserkreislaufes.

In the last 50 years, the population growth of urban areas has increased significantly in Latin America. While this growth is mainly concentrated in coastal cities, places that were less populated before and even misperceived as uninhabited, as the Amazonia, also present an urban population increase. The cities of Lamas and Santa Maria de Nieva belong to the network of Peruvian northern cities: they are located in a transverse axis connecting the coast (Piura, Chiclayo) with the lower Amazonia (Iquitos). Taking into account the characteristics of land occupation, using cartographic sources (maps and satellite images) and gathering data from field research conducted during the month of August 2015, a first analysis of the urban water cycle was performed. It is based on the idea that this cycle is not only carry out in urban areas but rather has a close relationship with the territory (and resources) surrounding both locations. The results show that both cities have a significant impact (negative and positive) in the water sources and wastewater discharges of the territory. It has also been found that inside the urban space, water is an element that configures or sets sub-zones. / En los últimos 50 años, el crecimiento de la población que vive en zonas urbanas se ha incrementado de manera notable en Latinoamérica. Si bien este crecimiento se concentra principalmente en las ciudades costeras, espacios antes menos poblados e incluso percibidos erróneamente como deshabitados, como la Amazonía, también presentan un incremento poblacional urbano. Las ciudades de Lamas y Santa María de Nieva pertenecen a la red de ciudades del norte del Perú: están situadas en un eje transversal que conecta la costa (Piura, Chiclayo) con la baja Amazonía (Iquitos). Teniendo en cuenta las características de ocupación del territorio y a través de un levantamiento de información de campo realizado durante el mes de agosto del 2015, sumado a la utilización de fuentes cartográficas (mapas e imágenes satelitales) se realizó un primer análisis del ciclo urbano del agua, basado en la idea de que este ciclo no sólo se realiza de manera íntegra en el ámbito urbano y que evidentemente presenta una relación estrecha con el territorio (y sus recursos) que rodea a ambas localidades. Los resultados obtenidos muestran que a nivel fuentes de agua y retorno de las aguas utilizadas, ambas localidades tienen un gran impacto (negativo y positivo) en el territorio; además, se pudo identificar que dentro del espacio urbano el agua también es un elemento que configura o delimita sub-zonas.