1,721,206 research outputs found
Nature-based mitigation of flood risks by mangrove forests in a tropical river delta
No full textAbstract: River deltas and estuaries are densely populated regions but face coastal flood risks due to extreme sea level events, particularly as climate change leads to rising sea levels and more instense storms. Nature-based strategies, such as the conservation and restoration of mangroves, are increasingly considered a cost-effective and sustainable addition to traditional flood defences. Cities such as Guayaquil (Ecuador), Ho Chi Minh (Vietnam) and Khulna (Bangladesh) all house millions of people but despite their growing exposure to coastal floods, the mangroves in between these cities and the sea have been largely lost to aquaculture. Yet, how the largescale conversion from mangrove to human land use affects the propagation of flood waves is still unknown. This thesis attempts to fill that knowledge gap by elaborating on how extreme sea levels are heightened or lowered when propagating through a tropical delta, and how this depends on the spatial properties of the complex network of mangroves, estuarine channels and human land use that is intrinsic to most tropical deltas. Hydrodynamic models allow the study of flood wave propagation over the tens to hundreds of kilometres that tropical river deltas typically cover. In this thesis, we present the setup, calibration and evaluation of a hydrodynamic model of the Guayas delta, Ecuador. The model demonstrated that the current mangroves in the delta effectively attenuate incoming extreme sea levels related to El Ni\uf1o events and prevent the increase in sea level to amplify upstream. Furthermore, we show that the spatial locations of mangroves and aquaculture have a large impact on the attenuation of extreme sea levels with the strongest reduction in case mangroves are uniformly spread over the delta or concentrated upstream. During a field campaign, we measured high water level attenuation in a tropical Rhizophora forest, where aerial roots are several metres high, revealing attenuation rates up to 46 \ub1 9.8 cm/km, which are the highest attenuation rates ever recorded in a mangrove forest. With this thesis, we show how mangrove ecosystem properties and their spatial location within deltas affect the reduction of extreme water levels when propagating through the complex web of mangroves, channels and aquaculture, which is intrinsic to many tropical river deltas. Human infrastructure in the deltaic plain is often essential for the economic development of these regions, yet this thesis elaborates on where conversion from mangroves to human land use has minor effects on the reduction of high water levels
Potential for nature-based mitigation of coastal flood risks : from regional to global scale assessments
No full textSpatial patterns and bio-geomorphological effects of vegetation loss in a submerging coastal marsh
No full textWetlands for dry land : role of bio-physical interactions in tidal marshes for nature-based shoreline protection
No full textAbstract: Global climate changes impose multiple challenges, including the increasing risk of coastal flood hazards due to sea level rise and increasing impact of storm activity. Social and economic cost of flood hazards are huge since low elevated coastal zones often house densely populated and industrialized communities. Hence, there is a strong urge to implement sustainable climate adaptation strategies. In this context, nature-based shoreline protection approaches such as conservation or (re)creation of tidal marsh ecosystems provide multiple opportunities. Nevertheless, effective implementation of tidal marsh ecosystems as a complementary shoreline protection is hampered by the uncertainties about their effectiveness and reliability. This thesis elaborates on the role of species-specific plant traits, how they vary spatially and over time, how they interact with hydrodynamics and sediment dynamics and, how these feedbacks contribute to the shoreline protection capacity of tidal marshes. Field monitoring and field experiments were done along the brackish part of the Elbe estuary, Germany and flume experiments took place in the Large Wave Flume, Hannover, Germany and the Mesodrome tidal flume facility, Antwerp, Belgium. This thesis provides new insights in the role of species-specific plant traits within the mutual interactions between hydrodynamic forces, sediment dynamics and vegetation that are crucial in understanding the spatial-temporal shoreline protection efficiency of tidal marshes. We show that hydrodynamic forces from waves and currents form a not to be neglected additional stressor for plant growth and survival and we illustrate how these forces constrain suitable conditions for successful tidal marsh conservation, restoration and creation. Moreover, we argue how providing enough space to allow marsh expansion will increase the resilience and reliability of the nature-based shoreline protection function of tidal marsh in a changing climate
How effective are tidal marshes as nature‐based shoreline protection throughout seasons?
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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