[en] The aim of this thesis is to study the possible effects of natural climatic variation and global climatic change on maximum and average flows. These flows are estimated in order to solve problems related to the planning and design of complex hydric systems large basins in large extensions of land. For this reason, the Neuquén river basin, with a total area of 30,843 km2 (Paso de los Indios, Neuquén province) and the Paraná river basin, with a total area of 1,950,000 km2 (Corrientes, Corrientes province) have been selected. Works of hydraulic energy are carried out so as to control both hydric excess and deficit, and to achieve a better distribution in time and space of the surface runoff, especially in a country like Argentina, which has arid and semiarid climates in two thirds of its total surface. The nucleus of the present study is connected to the application of probabilistic methods for the detection of multiple points of change associated with a natural climatic variability. The presence of different periods with flows showing diverse statistic properties has been defined and their influence over hydrological design parameters has been evaluated. The identification of points of change in the series of maximum flows has been performed through the application of two types of statistical tests: parametric and nonparametric. The former imply knowing the point or points of change and therefore both the likelihood ratio test (Gamma model) and the regression model have been used. The Mann-Kendal and Pettitt tests have been used for the latter. The possibility of detecting multiple points of change was conducted with a method based on U-statistics, and it allowed for a validation of the association between natural climatic change and the changes observed in the maximum flows of the selected systems as from the 1970s. This identification of the flow periods with different statistical properties enable us to direct a second look over the infrastructure so as to evaluate the vulnerability associated with natural climatic variability and anthropogenic climatic change. Anthropogenic climatic change and its effects on the hydrological system is a subject of scientific research which implies the development of new mathematical models of general atmospheric circulation for an estimation of its diverse effects on hydrological variables, in average values applicable to planning hydrological systems in large basins. A regression model has been applied to evaluate the effects of two scenarios of average rainfall over medium-sized basins in Patagonia. The analysis of long-term persistence in hydrological series is an issue that connects to the identification of relationships between the climate and the flows in different scales. The multifractality of hydrological series has been studied and the Hurst parameter has been estimated given its influence in detection tests and the parameters of extreme value models. Results of numeric experiments are presented in order to study the origins of multifractality, the asymmetry of the spectrum, and the variation in an indicator of predictability for different periods of time for extended series.

[gl] Esta Tese ten como obxectivos estudar os posibles efectos da variabilidade climática natural e mais do cambio climático global sobre los caudais máximos y medios. Estes caudais son estimados para resolver problemas de planificación y deseño en sistemas hídricos complexos de concas hidrográfica de moita extensión. Por esta razón, foron seleccionadas as concas do río Neuquén e do río Paraná. As obras de enxeñaría hidráulica constrúense para controlar os excesos e os déficits hídricos, e tamén para lograr unha mellor distribución espacial e temporal do desaugue superficial ou enxurrada, especialmente nun país, como a Arxentina, que presenta dous terzos da su superficie con climas áridos e semiáridos. O núcleo do estudio levado a cabo relacionase ca aplicación de modelos probabilísticos para detectar puntos de cambio múltiples, asociados a variabilidade climática natural. Definiuse a presenza de distintos períodos con caudais que presentan diferentes propiedades estatísticas y avaliouse a su influencia sobre os parámetros do deseño hidrolóxico. A identificación de puntos de cambio nas series de caudais máximos realizouse aplicando probas estatísticas de dous tipos: paramétricas e non paramétricas. As primeiras implican coñecer o ou os punto de cambio y polo tanto utilizouse a proba de razón de verosimilitude (modelo Gamma) e o modelo de regresión. Entre as segundas aplicáronse, as probas de Mann-Kendal e de Pettitt. A posibilidade de detectar puntos de cambio múltiples foi avaliada cun método baseado nun novo estatístico e permitiu validar a asociación entre variabilidade climática natural cos cambios observados nos caudais máximos dos sistemas seleccionados a partir da década dos anos 70. Esta identificación dos períodos de caudais con distintas propiedades estatísticas permite orientar unha segunda mirada sobre a infraestrutura para avaliar a vulnerabilidade hidrolóxica que vai asociada ca variabilidade climática natural e co cambio climático antropoxénico. O cambio climático antropoxénico e os seus efectos sobre o ciclo hidrolóxico e un tema de investigación científica que implicou o desenvolvemento de novos modelos matemáticos de circulación xeral da atmosfera para a estimación dos efectos sobre as variables hidrolóxicas; estes modelos aplícanse de cotío os valores medios na planificación de sistemas hidrolóxicos en grandes concas. Por iso, neste traballo, aplicase un modelo de regresión para avaliar os efectos de dous escenarios de precipitacións medias sobre os caudais medios en concas da Patagonia. O análises da persistencia de largo prazo en series hidrolóxicas e un tema que se conecta ca identificación de relacións entre o clima e os caudais a distintas escalas. Estudouse a multifractalidade de series hidrolóxicas e estimouse o parámetro de Hurst, debido a súa influencia en probas de detección e nos análises de valores extremos. En consecuencia, preséntanse resultados de experimentos numéricos para estudar os orixines da multifractalidade, da asimetría do espectro multifractal e da variación nun indicador de la predictibilidade para distintos períodos de tempo cando están dispoñibles series hidrolóxicas extensas.