Abstract:Extreme streamflow values estimates are important for flood risk assessment and also for the design and operation of hydraulic structures. The behavior of this hydrological variable is under climate and land use changes effects and river's course modifications caused by construction and operation of large reservoirs. The assumption of stationarity commonly adopted in flood frequency and magnitude analysis studies is questionable under such circumstances. In this work we identified nonstationary annual maximum … Show more
“…Future studies could involve evaluating model uncertainties (BLAZKOVA;BEVEN, 2002;ZENG et al, 2016), as well as the shape and distribution of design hyetographs (e.g., Grimaldi et al, 2012). We also did not consider a possible nonstationarity of discharges existent in the Itajaí-Açu basin, although some studies have suggested its existence in Southern Brazil (e.g., Bartiko et al (2017)), and this suggests further developments for this topic.…”
Design hydrographs are widely used in practical hydrologic engineering problems. Typical applications adopt event-based (EBM) methods, using rainfall-runoff models to convert design hyetographs into design hydrographs. Uncertainties include the definition of antecedent conditions and the assumption of equivalence between hyetograph and hydrograph return periods. An alternative is to use continuous simulation (CSM) methods, by forcing a rainfall-runoff model with long precipitation series, and directly analyzing the output discharges. To better understand uncertainties in the EBM method and differences between CSM and EBM ones, we applied a hydrological model in the Itajaí-Açu river basin to compare a CSM method with 730 different simulations of an EBM one, considering different basin antecedent conditions and design hyetographs (10- and 50-years). Results indicated that the EBM method leads to a large range of design discharges depending on the antecedent condition. CS-based 10- and 50-years maximum discharges corresponded to percentiles between 30% and 50% of the EBM estimates. Higher discharge variation occurred in sub-basins with larger maximum soil water storage. Our conclusions agree with the literature, which points towards CSM-based methods to estimate design discharges.
“…Future studies could involve evaluating model uncertainties (BLAZKOVA;BEVEN, 2002;ZENG et al, 2016), as well as the shape and distribution of design hyetographs (e.g., Grimaldi et al, 2012). We also did not consider a possible nonstationarity of discharges existent in the Itajaí-Açu basin, although some studies have suggested its existence in Southern Brazil (e.g., Bartiko et al (2017)), and this suggests further developments for this topic.…”
Design hydrographs are widely used in practical hydrologic engineering problems. Typical applications adopt event-based (EBM) methods, using rainfall-runoff models to convert design hyetographs into design hydrographs. Uncertainties include the definition of antecedent conditions and the assumption of equivalence between hyetograph and hydrograph return periods. An alternative is to use continuous simulation (CSM) methods, by forcing a rainfall-runoff model with long precipitation series, and directly analyzing the output discharges. To better understand uncertainties in the EBM method and differences between CSM and EBM ones, we applied a hydrological model in the Itajaí-Açu river basin to compare a CSM method with 730 different simulations of an EBM one, considering different basin antecedent conditions and design hyetographs (10- and 50-years). Results indicated that the EBM method leads to a large range of design discharges depending on the antecedent condition. CS-based 10- and 50-years maximum discharges corresponded to percentiles between 30% and 50% of the EBM estimates. Higher discharge variation occurred in sub-basins with larger maximum soil water storage. Our conclusions agree with the literature, which points towards CSM-based methods to estimate design discharges.
“…Recently, Bartiko et al (2017) also found clusters of increasing annual maximum daily flow in the Upper Uruguay basin. However, since large water flows in SB are linked to recurrent climatic features such as the ENSO phenomena (Krepper et al, 2003;Maciel et al, 2013;Pasquini & Depetris, 2007;Robertson & Mechoso, 1998;Silva et al, 2017), the nonstationarity in the flood time series might be related to oscillatory components rather than to a linear trend.…”
Section: Water Resources Researchmentioning
confidence: 87%
“…In Southern Brazil (SB) there were increases in annual average, minimum, and maximum streamflow (Bartiko et al, 2017;Berbery & Barros, 2002;Detzel et al, 2016;Doyle & Barros, 2011;Hirata et al, 2010;Marques, 2012;Pasquini & Depetris, 2007), generally associated with rainfall variability (Doyle & Barros, 2011;Maciel et al, 2013;Saurral et al, 2008). The Uruguay and the Paraná rivers, which downstream become the La Plata River, have experienced in the last century one of the greatest annual streamflow increases in the world (Milliman et al, 2008;Piao et al, 2007).…”
The replacement of natural forests with agriculture is generally associated with modifications in the hydrological behavior of a basin. This is particularly notable in the tropics and subtropics. Southern Brazil is a region with extensive agricultural production, forest conservation, and a vast unexplored streamflow data despite substantial rainfall trends observed in recent decades. In this work, we explore trends in the streamflow regime in the majority of the monitored basins in Southern Brazil. Additionally, we evaluate if pristine forested basins and agricultural nonforested basins have significantly different streamflow responses to changes in rainfall. We analyzed annual averages, maxima, minima, and seasonality of a 36‐year data set (1975–2010) of 675 rainfall and 140 streamflow gauges. Results reveal that large trends are widespread in Southern Brazil, especially in basins with areas smaller than 10,000 km2. Changes in the rainfall regime did not directly translate into changes in the streamflow regime. Changes in the annual maximum flow of forested basins were not statistically significant even when the annual average and maximum rainfall increased significantly. Correlations between changes in rainfall and streamflow for two indices, namely, duration of low‐magnitude events and seasonality, were statistically significant (p < 0.05) only for agricultural basins. The results indicate a higher propagation of hydrological changes through anthropogenically modified systems, providing evidence that agricultural basins are more sensitive to changes in the rainfall regime.
“…Devido à possibilidade de ocorrerem alterações nas estatísticas das séries hidrológicas ao longo do tempo, diversos estudos buscaram avaliar a estacionariedade de séries históricas em bacias hidrográficas de diferentes regiões do mundo (Marengo, 2004;Yeste et al, 2018;Wilcox et al, 2018;Sun et al, 2018;Harrigan et al, 2018;Gu et al, 2019;Forootan, 2019;Mirdashtvan et al, 2020;Stephens e Bledsoe, 2020). No Brasil, detecta-se viés tanto de incremento quanto de decréscimo da vazão em diversas bacias e, em boa parte dos estudos, notam-se mudanças significativas após a década de 70 (Genta et al, 1998;Müller et al, 1998;Bartiko et al, 2017;Tozzi e Fill, 2020). Tendências de aumento das vazões são relatadas por Genta et al (1998), Müller et al (1998), Gueter e Prates (2002), Sáfadi (2004), Rosin et al (2015), e Teixeira et al (2020).…”
Section: Introductionunclassified
“…Viés decrescente é relatado por Moraes et al (1998), Marengo e Alves (2005) e Melo et al (2019). No Sul do Brasil, as afluências mostraram-se não-estacionárias nos estudos de Detzel et al (2011) e Bartiko et al (2017). Com relação às séries de precipitação no Brasil, relatase tanto viés crescente (Berlato e Cordeiro;Nunes et al, 2018;Quadros et al, 2018;Guedes et al, 2019) como decrescente (Santos e Nishiyama, 2016), e ainda ausência de tendência (Sá et al, 2018;Alcântara et al, 2019;Melo et al, 2019).…”
This study aims to analyze the stationariety and homogeneity of rainfall and streamflow series of the contribution basin of Castro Alves Hydroeletric Power Plant, in Southern Brazil. The rainfall data were acquired from the Agência Nacional de Águas, and the average rainfall series was calculated for the period from 1945 to 2017. The streamflow data were acquired from the Operador Nacional do Sistema Elétrico covering a period from 1945 to 2017. The analysis were performed in the complete series and in two periods obtained from the same, referring to the period before and after 1970. Six statistical tests were used to check the stationarity: t-Student, F-Snedecor, Spearman Correlation Coefficent, Cox-Stuart, Mann-Whitney and Mann-Kendall. The verification of the point of change in the series of total annual precipitations, monthly totals and monthly average flows was performed using Pettitt’s test. The analysis results made it possible to conclude that the hydrological series are non-stationary. The period prior to 1970 was characterized as non-stationary. The period after 1970 showed significant signs of stationarity and homogeneity for both variables. Using the Pettitt test, a trend change was identified in the year 1971 and 1970 for the series of annual total precipitations and monthly mean flows, respectively. In the monthly analyzes of the series, it was found that the increase in the precipitated total was more accentuated in the dry months of May and November. This corroborates the more pronounced increase in the average monthly streamflow observed in those same months.
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