Influência das alterações climáticas em bacias de retenção
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2015-12-01
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As bacias de retenção permitem controlar os caudais crescentes pelo aumento do
coeficiente de escoamento resultante da impermeabilização do solo devido à construção do
elevado número de vias de comunicação. Em Portugal, o dimensionamento de bacias de
retenção é realizado com base nas curvas de Intensidade-Duração-Frequência (IDF)
regulamentados pelo Decreto Regulamentar (DR) nº23/95 de 23 de Agosto. No entanto,
alterações observadas no clima passado recente e projeções para o clima futuro apontam
para diferenças no regime da precipitação em Portugal, em particular, na frequência e
intensidade de eventos extremos o que sugere a necessidade de avaliar o impacto dos
efeitos de eventuais alterações climáticas nas curvas IDF.
Dados de precipitação horária observada fornecidos pelo Sistema Nacional
Informação Recursos Hídricos (SNIRH) e de precipitação diária simulados pelo modelo
Consortium for Small-Scale Modelling–Climate version of the Local Model (COSMOCLM)
para cenários futuros e do passado recente foram desagregados para escalas horárias
(método dos Fragmentos) e sub-horárias (coeficientes de desagregação indicados em
Brandão et. al., 2001) Após a análise estatística exploratória preliminar, a Lei de Gumbel
foi ajustada às séries temporais de intensidade de precipitação máxima para dez valores de
duração e utilizada para estimar intensidades de precipitação máxima para oito valores de
períodos de retorno. Os parâmetros (a e b) das curvas IDF ( = × ) foram depois
estimados pelo método dos mínimos quadrados e pelo ajuste robusto. A metodologia
descrita foi aplicada a ambos os conjuntos de dados observados e simulados e os resultados
foram comparados, após corrigir o viés introduzido pelo modelo COSMO-CLM, em
relação aos resultados obtidos com os dados observados por Brandão et al. (2001) e por
Matos e Silva (1986) com os dados observados. A metodologia adotada e desenvolvida
garante a robustez, a significância estatística e a adequada análise comparativa dos
resultados obtidos. O dimensionamento efetuado com as curvas IDF para os cenários de
clima futuro sugere a necessidade do aumento da dimensão destes órgãos de drenagem e
que esta variação não será idêntica nas três regiões pluviométricas nem no interior de cada uma destas regiões.
Retention basins allow controlling the flow rates amplified by the increase of coefficient of runoff resulting from soil impermeabilization due to the construction of the high number of communication channels (roads, freeways). In Portugal, the design of retention basins is based on the intensity-duration-frequency (IDF) curves regulated by Regulatory Decree n.º23/95 of 23rd August 1995. However, observed changes in recent past climate and projections for future climate suggest differences in precipitation regime in Portugal, in particular respecting to the frequency and intensity of extreme events, thus leading to the need to evaluate the impact of potential climate change on IDF curves. Observed hourly precipitation data provided by the National Information System for Water Resources (Sistema Nacional de Informação de Recursos Hídricos, SNIRH) and daily precipitation simulated by the Consortium for Small-Scale Modeling Climate-version of the Local Model (COSMO-CLM) for recent past and future scenarios were disaggregated to hourly (using the method of fragments) and sub-hourly scales (using disaggregation coefficients as suggested by Brandão et. al., 2001). After an exploratory statistical analysis, the Gumbel distribution function was fitted to the time series of maximum precipitation intensity for a set of ten durations (5, 10, 15, 30 and 60 minutes, and 2, 6, 12, 24 and 48 hours) and used to estimated maximum precipitation intensities for eight return periods (2, 5 , 10, 50, 100, 500 and 1000 years). Parameters a and b of the IDF curves ( = × ) were then estimated by the least squares method and the robust regression. The described methodology was applied to both sets of observed and simulated data and the results were compared after correcting the bias introduced by the COSMOCLM model, in relation to the results obtained by Brandão et al. (2001) and by Matos and Silva (1986) with the observed data. The adopted methodology ensures the robustness, statistical significance and adequate comparative analysis of the results. The retention basin design performed with IDF curves developed for future climate scenarios suggests the need to increase the size of these drainage systems and this change is not the same in the three rainfall regions or even within each of these regions.
Retention basins allow controlling the flow rates amplified by the increase of coefficient of runoff resulting from soil impermeabilization due to the construction of the high number of communication channels (roads, freeways). In Portugal, the design of retention basins is based on the intensity-duration-frequency (IDF) curves regulated by Regulatory Decree n.º23/95 of 23rd August 1995. However, observed changes in recent past climate and projections for future climate suggest differences in precipitation regime in Portugal, in particular respecting to the frequency and intensity of extreme events, thus leading to the need to evaluate the impact of potential climate change on IDF curves. Observed hourly precipitation data provided by the National Information System for Water Resources (Sistema Nacional de Informação de Recursos Hídricos, SNIRH) and daily precipitation simulated by the Consortium for Small-Scale Modeling Climate-version of the Local Model (COSMO-CLM) for recent past and future scenarios were disaggregated to hourly (using the method of fragments) and sub-hourly scales (using disaggregation coefficients as suggested by Brandão et. al., 2001). After an exploratory statistical analysis, the Gumbel distribution function was fitted to the time series of maximum precipitation intensity for a set of ten durations (5, 10, 15, 30 and 60 minutes, and 2, 6, 12, 24 and 48 hours) and used to estimated maximum precipitation intensities for eight return periods (2, 5 , 10, 50, 100, 500 and 1000 years). Parameters a and b of the IDF curves ( = × ) were then estimated by the least squares method and the robust regression. The described methodology was applied to both sets of observed and simulated data and the results were compared after correcting the bias introduced by the COSMOCLM model, in relation to the results obtained by Brandão et al. (2001) and by Matos and Silva (1986) with the observed data. The adopted methodology ensures the robustness, statistical significance and adequate comparative analysis of the results. The retention basin design performed with IDF curves developed for future climate scenarios suggests the need to increase the size of these drainage systems and this change is not the same in the three rainfall regions or even within each of these regions.
Descrição
Dissertação de Mestrado em Engenharia Civil
Palavras-chave
Alterações clímáticas , Precipitação extrema , Curvas IDF , Dimensionamento de bacias de retenção