Effects of climate change on wave climate and consequent coastal impacts : application to the Catalan coast (NW Mediterranean Sea)
ColaboratorSierra, J. P. (Joan Pau); Universitat Politècnica de Catalunya. Escola Tècnica Superior d'Enginyers de Camins, Canals i Ports de Barcelona
Document typeDoctoral thesis
PublisherUniversitat Politècnica de Catalunya
Rights accessOpen Access
Tesi per compendi de publicacionsClimate change is a hot research topic due to the consequent impacts on our environment in the near future. The last report of the International Panel on Climate Change¿the leading international body for assessment of climate change¿highlights a lack of information on the potential changes in wave climate and, consequently, on their coastal impacts. The problem is largely complicated because wave forcing is affected by a number of uncertainty factors, being the choice of the climate model one of the most relevant. The main purpose of this thesis is to provide a better understanding of the future wave climate in the area of interest: the Catalan coast, which is located in the NW part of the Mediterranean Sea, a basin particularly exposed to climate change. Based on previous studies, three methodological approaches are explored to address this issue: trend analysis, dynamical modelling and statistical modelling. The thesis work results in the generation and analysis, for the first time in this area, of a high temporal and spatial resolution database of future wave projections. The use in this thesis of atmospheric projections obtained by five combinations of regional-global climate models enables the study of the inter-model variability in terms of wave parameters. The results illustrate, for the winter season, the large variability associated to the parent global circulation model (particularly for the wave direction, a wave variable that seems to be especially affected by climate change in this area). In most of the domain, wave height and wave period tend to generally decrease for both mean and stormy conditions but extremes are associated to a large uncertainty. As expected, these changes are closely related to those of the (wave forcing) surface wind speed but fetch also plays an important role. For favourable fetch conditions (waves coming from east) wave climate changes are more accentuated and to the percentage of mixed sea states tends to increase. The second important contribution of this thesis is related with the methodology. New approaches of trend analysis that take into consideration the nature of the data are presented. Also, especial emphasis is given to the uncertainty analysis in order to detect statistically significant changes. In this regard, bootstrapping is shown to be a simple but effective method if adequately modified. Nevertheless, the most significant methodological contribution is perhaps the development of a new (computationally inexpensive) statistical method to model wave heights, that greatly improves the model performance at nearshore areas. The frequency and directional dispersion theory of wave propagation is used to explicitly model swell waves, making use of the principal component analysis to simplify the forcing into a set of representative atmospheric patterns. Finally, from an engineering perspective, this thesis reviews and quantifies the main physical impacts that changes in ocean wave patterns can have on coastal areas. It is found that mild variations of forcing wave conditions can greatly affect coastal processes, due to their non-linear relation. For example, longshore sediment transport can vary at a rate higher than 100% caused by a rotation of the mean wave direction of only 10º. Getting into more detail, a couple of case studies on the Catalan coast analyse the affectation on harbour agitation and longshore sediment transport on beaches.
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