73 research outputs found
A regional Bayesian POT model for flood frequency analysis
Flood frequency analysis is usually based on the fitting of an extreme value
distribution to the local streamflow series. However, when the local data
series is short, frequency analysis results become unreliable. Regional
frequency analysis is a convenient way to reduce the estimation uncertainty. In
this work, we propose a regional Bayesian model for short record length sites.
This model is less restrictive than the index flood model while preserving the
formalism of "homogeneous regions". The performance of the proposed model is
assessed on a set of gauging stations in France. The accuracy of quantile
estimates as a function of the degree of homogeneity of the pooling group is
also analysed. The results indicate that the regional Bayesian model
outperforms the index flood model and local estimators. Furthermore, it seems
that working with relatively large and homogeneous regions may lead to more
accurate results than working with smaller and highly homogeneous regions
Assessing recent trends in high-latitude Southern Hemisphere surface climate
Understanding the causes of recent climatic trends and variability in the high-latitude Southern Hemisphere is hampered by a short instrumental record. Here, we analyse recent atmosphere, surface ocean and sea-ice observations in this region and assess their trends in the context of palaeoclimate records and climate model simulations. Over the 36-year satellite era, significant linear trends in annual mean sea-ice extent, surface temperature and sea-level pressure are superimposed on large interannual to decadal variability. However, most observed trends are not unusual when compared with Antarctic paleoclimate records of the past two centuries. With the exception of the positive trend in the Southern Annular Mode, climate model simulations that include anthropogenic forcing are not compatible with the observed trends. This suggests that natural variability likely overwhelms the forced response in the observations, but the models may not fully represent this natural variability or may overestimate the magnitude of the forced response
Genomic comparisons reveal biogeographic and anthropogenic impacts in the koala (Phascolarctos cinereus): a dietary-specialist species distributed across heterogeneous environments
The Australian koala is an iconic marsupial with highly specific dietary requirements distributed across heterogeneous environments, over a large geographic range. The distribution and genetic structure of koala populations has been heavily influenced by human actions, specifically habitat modification, hunting and translocation of koalas. There is currently limited information on population diversity and gene flow at a species-wide scale, or with consideration to the potential impacts of local adaptation. Using species-wide sampling across heterogeneous environments, and high-density genome-wide markers (SNPs and PAVs), we show that most koala populations display levels of diversity comparable to other outbred species, except for those populations impacted by population reductions. Genetic clustering analysis and phylogenetic reconstruction reveals a lack of support for current taxonomic classification of three koala subspecies, with only a single evolutionary significant unit supported. Furthermore, similar to 70% of genetic variance is accounted for at the individual level. The Sydney Basin region is highlighted as a unique reservoir of genetic diversity, having higher diversity levels (i.e., Blue Mountains region; AvHe(corr)-0.20, PL% = 68.6). Broad-scale population differentiation is primarily driven by an isolation by distance genetic structure model (49% of genetic variance), with clinal local adaptation corresponding to habitat bioregions. Signatures of selection were detected between bioregions, with no single region returning evidence of strong selection. The results of this study show that although the koala is widely considered to be a dietary-specialist species, this apparent specialisation has not limited the koala's ability to maintain gene flow and adapt across divergent environments as long as the required food source is available
Factores que determinan la acción de chatear por celular mientras se camina
1 recurso en línea (97 páginas) : ilustraciones, figuras, tablas.El presente trabajo de investigación estudia los factores que determinan la acción
de chatear mientras se camina, con el propósito de analizar sus causas, desde la
perspectiva de los usuarios, y plantear medidas que ayuden a mitigar la conducta
de chatear mientras se camina de los peatones.
La metodología usada tuvo dos perspectivas basadas en la aplicación de una
encuesta a una muestra representativa de la población. En primer lugar, se hizo un
análisis empírico a partir de la obtención de barras apiladas divergentes, para un
conjunto de indicadores de variables latentes, basados en indicadores de tipo Likert.
En segundo lugar, tomando los datos de un experimento de preferencias
declaradas, mediante un proceso iterativo, se hizo la estimación de modelos de tipo
Logit multinomial a través del software de uso libre Biogeme.
De esta manera se pudo concluir que los factores determinantes de la conducta de
chatear mientras se caminan están relacionados con características sociales del
individuo, políticas de tránsito, características de la infraestructura urbana,
características socio-económicas de las personas, así como las características
propias del uso del teléfono de cada individuo.Bibliografía y webgrafía: páginas 94-97.PregradoIngeniero de Transport
Comparison of uncertainty sources for climate change impacts: flood frequency in England
This paper investigates the uncertainty in the impact of climate change on flood frequency in England, through the use of continuous simulation of river flows. Six different sources of uncertainty are discussed: future greenhouse gas emissions; Global Climate Model (GCM) structure; downscaling from GCMs (including Regional Climate Model structure); hydrological model structure; hydrological model parameters and the internal variability of the climate system (sampled by applying different GCM initial conditions). These sources of uncertainty are demonstrated (separately) for two example catchments in England, by propagation through to flood frequency impact. The results suggest that uncertainty from GCM structure is by far the largest source of uncertainty. However, this is due to the extremely large increases in winter rainfall predicted by one of the five GCMs used. Other sources of uncertainty become more significant if the results from this GCM are omitted, although uncertainty from sources relating to modelling of the future climate is generally still larger than that relating to emissions or hydrological modelling. It is also shown that understanding current and future natural variability is critical in assessing the importance of climate change impacts on hydrology
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