1,721,081 research outputs found
Contribution to modeling of soil-plant-atmosphere interactions and coupled hydro-geophysical data assimilation
Full text linkUnderstanding the complex feedback mechanisms regulating the land-atmosphere system has become a scientific imperative, as human induced changes may impact the stability of the Biosphere, both locally and globally. The present thesis work aims at improving current understanding and forecasting capabilities of the Soil-Plant-Atmosphere (SPA) continuum. To this purpose a numerical model of soil moisture dynamics is coupled with plant transpiration and photosynthesis. Soil moisture dynamics is modeled by the 3-D Richards equation and plant uptake is described by an Ohm's law type model accounting for water potential gradients and root, xylem and stomatal conductances. The transpiration flux from soil to the atmosphere is driven by the leaf water potential which is controlled by both local soil moisture conditions and atmospheric forcing. The hydraulic model is linked to the atmosphere by the calculation of the stomatal conductance which is optimized for maximum carbon gain considering Fickian mass transfer of CO2 and H2O through stomata and a biochemical model of photosynthesis. The model is used to investigate competition for water among multiple tree rooting systems in a Loblolly pine (Pinus Taeda) plantation and then coupled with a crop growth module to investigate farmland productivity at the field scale. In order to provide a fully-coupled description of the SPA system, the soil-plant model is then coupled with a slab representation of the Atmospheric Boundary Layer (ABL) and used to investigate the role of water table fluctuations and free atmospheric state on convective rainfall initiation. Model results compared well with measurements of soil moisture, sap flow in the plant xylem as well as energy fluxes above the canopy and convective rainfall initiation time.
In order to deal with the high degree of uncertainty related to both measurement and model errors the applicability of a data assimilation algorithm has also been explored to incorporate physical measurements into the transient hydrological model. Given the recent development of indirect geophysical surveys to monitor soil-plant interactions in the vadose zone, we tested an innovative iterative particle filter approach for coupled hydro-geophysical inversion of Electrical Resistivity Tomography (ERT) data. Model results demonstrate the ability of the method to improve model prediction and estimate multiple model parameters and this work lays the foundation for application of the methodology to soil-plant-atmosphere modeling.La comprensione dei molteplici meccanismi che regolano l'interazione tra suolo, vegetazione e atmosfera è oggi divenuta un imperativo nel campo della ricerca scientifica, poichè numerose sono le conseguenze che la presenza antropica puo avere sulla stabilità della Biosfera, a livello sia globale che locale. Questo lavoro di tesi si propone l'obiettivo di sviluppare nuovi strumenti modellistici che consentano una più accurata comprensione e descrizione del sistema suolo-vegetazione-atmosfera. A tal fine, un modello di trapirazione e fotosintesi della vegetazione è stato introdotto in un codice numerico per la descrizione del flusso in mezzi porosi. La dinamica dell'umidita del suolo e descritta dall'equazione tridimensionale di Richards, mentre il trasporto d'acqua attraverso le radici ed all'interno della pianta e definito tramite un modello di resistenze e potenziali idrici basato sulla legge di Ohm. Il flusso traspirativo è regolato dal potenziale fogliare, a sua volta determinato da condizioni locali di umidità del suolo e dalle forzanti atmosferiche. Il modello idraulico di assorbimento radicale è collegato all'atmosfera tramite il calcolo della resistenza stomatica, determinata sulla base di un modello di ottimizzazione dell'apertura degli stomi che massimizza la fotosintesi (descritta per mezzo di un modello biochimico) e minimizza la traspirazione. Tale approccio modellistico è stato impiegato per comprendere i meccanismi di competizione tra diverse piante per l'assorbimento idrico in una piantagione di Pinus Taeda. Il modello è stato inoltre integrato con un modulo di crescita del mais (Zea mays L.) per studiare la produttività agricola alla scala di bacino. Al fine di descrivere in modo completo le interazioni fra vegetazione ed atmosfera, il modello è stato poi accoppiato con la dinamica dello strato limite planetario ed utilizzato per comprendere l'effetto della falda e delle condizioni dell'atmosfera libera sugli eventi di precipitazione dovuti alla formazione di nubi convettive. I risultati modellistici illustrati in questa tesi sono confrontati con osservazioni di contenuto d'acqua nel suolo, misure di flussi xilematici, flussi energetici al di sopra della canopy ed eventi convettivi di precipitazione, dimostrando le ottime capacità predittive del modello sviluppato.
Sia le osservazioni che i risultati numerici sono tuttavia caratterizzati da un certo grado di errore. Per ovviare a tale incertezza è stato pertanto studiato un algoritmo di assimilazione dei dati che consente di incorporare le osservazioni fisiche nel modello dinamico idrologico. Dal momento che recenti studi di settore si sono focalizzati sull'utilizzo di metodi geofisici indiretti per la caratterizzazione dei processi di interazione fra suolo e vegetazione, in questo lavoro di tesi è stato sviluppato un metodo particle filter iterativo per l'inversione idro-geofisica accoppiata di dati di tomografia elettrica. I risultati presentati in questa tesi dimostrano l'abilità del metodo proposto di migliorare le previsioni e stimare i parametri del modello e pongono le basi per un nuovo approccio alla simulazione numerica del sistema suolo-vegetazione-atmosfera
Improving Groundwater Modeling by Coupled HydroGeophysical Data Assimilation
No full textA sequential Bayesian approach for joint assimilation of hydrological and geophysical data in a variably saturated flow model is presented.
The study aims to improve simulation results and system understanding by assimilation of multiple type data using a Monte Carlo approach and avoiding the inversion of the geophysical measurements.
A SIR based particle filter data assimilation is implemented in a 3D variably saturated flow model.
Point measurements are directly assimilated in time while spatial information are blended in the simulation by assimilating Electrical Resistivity Tomography (ERT) measurements. To avoid the inversion of the latter, a forward 3D model of electrical current distribution is implemented as the
measurements model in the data assimilation algorithm. The connection with the hydrological parameters occurs via the Archie's law.
A synthetic test case is used to test the assimilation of pressure data, ERT data and the joint assimilation of pressure and ERT data. Performance of the proposed modelling approach are evaluated in terms of predicton efficiency and parameter estimation. Perspectives and limitations of
coupled hydrogeophysical data assimilation are discussed
Matching ecohydrological processes and scales of banded vegetation patterns in semi-arid catchments
No full textWhile the claim that water-carbon interactions result in spatially coherent vegetation patterning is rarely disputed in many arid and semi-arid regions, the significance of the detailed water pathways and other high frequency variability remain an open question. How the short temporal scale meteorological fluctuations form the long term spatial variability of available soil water in complex terrains due to the various hydrological, land surface and vegetation dynamic feedbacks, frames the scope of the work here. Knowledge of the detailed mechanistic feedbacks between soil, plants and the atmosphere will lead to advances in our understanding of plant water availability in arid and semi-arid ecosystems and will provide insights for future model development concerning vegetation pattern formation. In this study, quantitative estimates of water fluxes and vegetation productivity are provided for a semi-arid ecosystem with established vegetation bands on hillslopes using numerical simulations. A state-of-the-science process based ecohydrological model is used, which resolves hydrological and plant physiological processes at the relevant space and time scales, for relatively small periods (e.g. decades) of mature ecosystems (i.e. spatially static vegetation distribution). To unfold the mechanisms that shape the spatial distribution of soil moisture, plant productivity and the relevant surface/subsurface and atmospheric water fluxes, idealized hillslope numerical experiments are constructed, where the effects of soil-type, slope steepness and overland flow accumulation area are quantified. Those mechanisms are also simulated in the presence of complex topography features on landscapes. The main results are: (a) Short temporal scale meteorological variability and accurate representation of the scales at which each ecohydrological process operates are crucial for the estimation of the spatial variability of soil water availability to the plant root zone; (b) Water fluxes such as evapotranspiration, infiltration, runoff-runon and subsurface soil water movement have a dynamic short temporal scale behavior that determines the long term spatial organization of plant soil water availability in ecosystems with established vegetation patterns; (c) Hypotheses concerning the hydrological responses that can lead to vegetation pattern formation have to accommodate realistic and physically based representations of the fast dynamics of key ecohydrological fluxes
Hydro-geophysical monitoring and stochastic inverse modeling of a controlled irrigation experiment
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Ecohydrological changes after tropical forest conversion to oil palm
No full textGiven their ability to provide food, raw material and alleviate poverty, oil palm (OP) plantations are driving significant losses of biodiversity-rich tropical forests, fuelling a heated debate on ecosystem degradation and conservation. However, while OP-induced carbon emissions and biodiversity losses have received significant attention, OP water requirements have been marginalized and little is known on the ecohydrological changes (water and surface energy fluxes) occurring from forest clearing to plantation maturity. Numerical simulations supported by field observations from seven sites in Southeast Asia (five OP plantations and two tropical forests) are used here to illustrate the temporal evolution of OP actual evapotranspiration (ET), infiltration/runoff, gross primary productivity (GPP) and surface temperature as well as their changes relative to tropical forests. Model results from large-scale commercial plantations show that young OP plantations decrease ecosystem ET, causing hotter and drier climatic conditions, but mature plantations (age > 8−9 yr) have higher GPP and transpire more water (up to +7.7%) than the forests they have replaced. This is the result of physiological constraints on water use efficiency and the extremely high yield of OP (six to ten times higher than other oil crops). Hence, the land use efficiency of mature OP, i.e. the high productivity per unit of land area, comes at the expense of water consumption in a trade of water for carbon that may jeopardize local water resources. Sequential replanting and herbaceous ground cover can reduce the severity of such ecohydrological changes and support local water/climate regulation.Deutsche Forschungsgemeinschaft 10.13039/501100001659Swiss National Science Foundatio
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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