1,721,049 research outputs found
Water scarcity is exacerbated in the south
No full textThe Southern Hemisphere has experienced a 20% drop in water availability in 20 years
Drought‐Rich Periods Are More Likely Than Flood‐Rich Periods in Brazil
Full text linkStreamflow exhibits persistent decadal variability; however, it is unclear if the magnitude and spatial extent of these variabilities are symmetric for droughts and floods. Here, we examine drought‐rich and flood‐rich periods in 319 streamflow gauges in Brazil from 1940 to 2020. Drought‐ and flood‐rich periods are detected by computing annual streamflow minima and maxima time series and using scan statistics to verify if events exceeding a threshold follow a Bernoulli process. We contrast streamflow time clustering with rainfall, evaporation, water abstraction, the Atlantic Multidecadal Oscillation (AMO), and the Pacific Decadal Oscillation (PDO). We detected a higher spatial frequency of drought‐ than flood‐rich periods. For 5‐year return period thresholds, drought‐rich periods are observed in 81% of the basins, 16.7 times the false positive rate (4.8%) and 4.7 times flood‐rich periods (17%). This asymmetry is linked with sharp increases in water abstractions since the 1990s and a higher prevalence of rainfall‐poor periods (41% of gauges) compared to rainfall‐rich (22% of gauges), which we interpret as being further amplified into drought‐rich periods due to an interannual persistence of water storage deficits. Brazil experienced a dry period until the 1960s, extensive flooding in the 1980s, and record low flows from the 2000s onward. Drought and flood‐rich periods are well aligned with rainfall clustering, water abstractions, the AMO and PDO. Droughts‐rich periods are more frequent in shorter time scales (several years to one decade) and flood‐rich periods in longer time scales (a few decades). Our findings highlight the nonlinearity and asymmetry of drought and flood change at decadal scales
Climate and land management accelerate the Brazilian water cycle
Full text linkIncreasing floods and droughts are raising concerns of an accelerating water cycle, however, the relative contributions to streamflow changes from climate and land management have not been assessed at the continental scale. We analyze streamflow data in major South American tropical river basins and show that water use and deforestation have amplified climate change effects on streamflow extremes over the past four decades. Drying (fewer floods and more droughts) is aligned with decreasing rainfall and increasing water use in agricultural zones and occurs in 42% of the study area. Acceleration (both more severe floods and droughts) is related to more extreme rainfall and deforestation and occurs in 29% of the study area, including southern Amazonia. The regionally accelerating water cycle may have adverse global impacts on carbon sequestration and food security
Process Controls on Flood Seasonality in Brazil
No full textA coincidence in the timing of floods and their drivers can be used as a proxy for the causality of flood generation. Here, we investigate the relationship between the seasonality of floods, maximum annual rainfall, and maximum annual soil moisture data of 886 basins in Brazil for 1980–2015 to shed light on process controls of flood generation. Floods tend to occur at the same time of year as soil moisture peaks and lag behind rainfall peaks by 3 weeks. In Amazonia, central and northern Brazil, flood timing is more correlated with the timing of soil moisture peaks than with that of rainfall peaks, which is interpreted as resulting from high subsurface water storage capacities. In southern and southeastern Brazil, on the other hand, flood timing is highly correlated with both soil moisture and rainfall because of low subsurface water storage capacities. These findings can support flood forecasting and climate impact studies
Desenvolvimento de um modelo de inundação bidimensional acelerado por GPGPU
Full text linkInundações causam enormes prejuízos econômicos e afetam a vida de milhares de pessoas. Elaborar medidas para mitigar os efeitos das inundações é uma tarefa que exige o uso de modelos que simulem com precisão e rapidez o processo de inundação. Diante disso, os objetivos deste trabalho foram: (i) desenvolver uma implementação paralela de um modelo de inundação bidimensional para ser executado em unidades de processamento gráfico de propósito geral (GPGPU) e (ii) determinar o ganho de desempenho em comparação com uma versão sequencial equivalente. Como estudo de caso, fez-se a simulação da inundação do Campus Trindade da bacia hidrográfica da Universidade Federal de Santa Catarina. A versão paralela do modelo foi desenvolvida utilizando linguagem de programação CUDA C e uma estrutura baseada numa versão sequencial do modelo de inundação implementada em linguagem FORTRAN. Este modelo utiliza uma formulação 2D das equações de águas rasas discretizada pelo método de diferenças finitas. Para o desenvolvimento do código computacional utilizou-se o software Visual Studio Community 2013 e CUDA toolkit 8. As simulações foram realizadas em um computador equipado com processador Intel® CoreTM i7-7700L 4.2GHz e GPU GeForce GTX 1060 6GB. Por meio das comparações entre os tempos de simulação verificamos que o modelo paralelo processado em GPGPU foi 70 vezes mais rápido que a versão sequencial executada na CPU, reduzindo o tempo de simulação de 12 horas para 10 minutos. Além disso, os resultados permitiram verificar a evolução do processo de inundação na bacia demonstrando que o uso de GPGPU é uma alternativa promissora na construção de modelos de inundação, para a previsão de cheias e emissão de alerta. Palavras chave: modelo de inundação, GPGPU, CUDAFil: Carlotto, Tomas. Universidad do Estado de Santa Catarina (Brasil).Fil: Innocente, Camyla. Universidad do Estado de Santa Catarina (Brasil).Fil: Lee, Seungsoo. Universidad do Estado de Santa Catarina (Brasil).Fil: Chaffe, Pedro. Universidad do Estado de Santa Catarina (Brasil)
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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