Impacto de alterações climáticas no dimensionamento de tubagens e órgãos de recolha de águas pluviais prediais
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2015-12-01
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O dimensionamento de infraestruturas de drenagem pluvial assenta implicitamente
no pressuposto de que a distribuicão da precipitacão intensa e estatisticamente estacionaria.
Esta hipótese e posta em causa pelas projecões do clima para o futuro, que apontam para um aumento da frequência e magnitude de eventos extremos de precipitação,
nomeadamente episódios de precipitação intensa que resulta na incerteza sobre o
desempenho futuro dos sistemas construídos sob o paradigma atual.
O objetivo deste estudo consiste na avaliação das potenciais consequências das
alterações climáticas no dimensionamento de orgãos de drenagem predial de águas pluviais e, consequentemente, na necessidade de rever regras e legislação sobre este
dimensionamento, recorrendo à análise comparativa das curvas de Intensidade-Duração-Frequência (IDF) definidas no Decreto Regulamentar no23/95 de 23 de Agosto, propostas por Matos e Silva (1986), e as obtidas com dados observados em estações meteorológicas representativas das três zonas pluviométricas preconizadas para Portugal em relação às obtidas com dados simulados pelo modelo regional de clima COSMO-CLM para cenários de clima passado (C20) e futuro (A1B e B1).
A metodologia adotada para o delineamento das curvas IDF, é baseada no estudo de
Brandão et al. (2001) e inclui: (i) o processo de desagregação da precipitação para escalas sub-diárias (método dos fragmentos) e sub-horárias (coeficientes de desagregação sugeridos em Brandão et al. 2001); (ii) a análise exploratória estatística preliminar e ajuste da função distribuição de Gumbel ajustada às séries temporais de intensidade de precipitação máxima para dez valores de duração; (iii) a utilização da função de distribuição de probabilidade inversa de Gumbel para estimar valores de intensidade de precipitação máxima para oito períodos de retorno; (iv) a linearização das curvas IDF com recurso a escalas logarítmicas e a estimação dos valores dos parâmetros a e b com a regressão robusta; e, (v) a correção do viés introduzido pelo modelo COSMO-CLM devido à sua dificuldade em reproduzir exatamente as condições observadas. A metodologia adotada e desenvolvida garante a robustez, a significância estatística e a adequada análise comparativa dos resultados obtidos e permite concluir que o impacto das alterações
climáticas no dimensionamento dos orgãos de drenagem predial pluvial se traduz, em
geral, pelo aumento da dimensão destes orgãos e que esta variação não deverá ser idêntica nas três regiões pluviométricas preconizadas para Portugal, nem no interior de cada uma destas regiões.
The design of stormwater drainage infrastructure relies on the implicit assumption that the intense precipitation distribution is statistically stationary. This assumption is questioned by the projections of climate change, which points to an increase of frequency of extreme precipitation events, including long drought periods and heavy precipitation episodes, resulting in high uncertainty about the future performance of systems constructed under this paradigm. The objective of this study is to assess the potential consequences of climate change in the design of drainage systems for rainwater and hence the need to review rules and legislation on this design, based on a comparative analysis between Intensity-Duration- Frequency (IDF) curves defined in the Regulatory Decree n o 23/95 of 23rd August, proposed by Matos and Silva (1986), and those obtained with observed data in meteorological stations representing the three rainfall zones recommended for Portugal compared to those obtained with data simulated by the COSMO-CLM regional climate model for recent past (C20) and future (A1B and B1) climate scenarios. The methodology adopted for the delineation of IDF curves, is based on study of Brandao et al. (2001) and includes: (i) precipitation disaggregation process for sub-daily (method fragments) and sub-hourly (disaggregation coefficients suggested by Brandao et al. 2001) scales; (ii) preliminary statistical exploratory analysis and fitting of the Gumbel distribution function to time series of maximum precipitation intensity for each of the ten durations; (iii) the use of the Gumbel inverse probability distribution to estimate maximum precipitation intensity values for eight return periods; (iv) linearization of IDF curves with logarithms and the estimation of the parameters a and b with robust regression after; and (v) correction of the bias introduced by the COSMO-CLM model dues to its difficulty in reproducing exactly the observed conditions . The methodology developed and ensures robustness, statistical significance and adequate comparative analysis of the results and suggest that the impact of climate change in the design of stormwater drainage organs building will imply, in general, the increase of the dimension of these organs and that this variation is not identical in all three rainfall regions defined for Portugal, or between stations within of these regions.
The design of stormwater drainage infrastructure relies on the implicit assumption that the intense precipitation distribution is statistically stationary. This assumption is questioned by the projections of climate change, which points to an increase of frequency of extreme precipitation events, including long drought periods and heavy precipitation episodes, resulting in high uncertainty about the future performance of systems constructed under this paradigm. The objective of this study is to assess the potential consequences of climate change in the design of drainage systems for rainwater and hence the need to review rules and legislation on this design, based on a comparative analysis between Intensity-Duration- Frequency (IDF) curves defined in the Regulatory Decree n o 23/95 of 23rd August, proposed by Matos and Silva (1986), and those obtained with observed data in meteorological stations representing the three rainfall zones recommended for Portugal compared to those obtained with data simulated by the COSMO-CLM regional climate model for recent past (C20) and future (A1B and B1) climate scenarios. The methodology adopted for the delineation of IDF curves, is based on study of Brandao et al. (2001) and includes: (i) precipitation disaggregation process for sub-daily (method fragments) and sub-hourly (disaggregation coefficients suggested by Brandao et al. 2001) scales; (ii) preliminary statistical exploratory analysis and fitting of the Gumbel distribution function to time series of maximum precipitation intensity for each of the ten durations; (iii) the use of the Gumbel inverse probability distribution to estimate maximum precipitation intensity values for eight return periods; (iv) linearization of IDF curves with logarithms and the estimation of the parameters a and b with robust regression after; and (v) correction of the bias introduced by the COSMO-CLM model dues to its difficulty in reproducing exactly the observed conditions . The methodology developed and ensures robustness, statistical significance and adequate comparative analysis of the results and suggest that the impact of climate change in the design of stormwater drainage organs building will imply, in general, the increase of the dimension of these organs and that this variation is not identical in all three rainfall regions defined for Portugal, or between stations within of these regions.
Descrição
Dissertação de Mestrado em Engenharia Civil
Palavras-chave
Hidráulica , Precipitação atmosférica , Alterações climáticas , Curvas IDF , Drenagem predial pluvial