Trend Analysis of Reference Evapotranspiration in the São Francisco River Basin, Brazil

An important requisite in any water resources management program is the knowledge of the natural processes that regulate the hydrological cycle, especially for spatial and temporal analyses of these processes. This work aimed to explore spatial and temporal trends of reference evapotranspiration (ETo), evaluate ETo variation dynamics and quantify the contribution of each one of the meteorological variables in ETo calculation in the São Francisco River basin. Daily data of maximum and minimum air temperature, mean relative air humidity, wind speed and net radiation from 101 weather stations, for the period from 1961 to 2015, were used and are part of the network of the National Institute of Meteorology (INMET). Climate trend analysis was performed using the non-parametric Mann-Kendall statistical test and the sensitivity analysis for the Penman-Monteith equation was carried out based on partial derivatives as a function of the key meteorological variables of ETo (air temperature, net radiation, wind speed and actual water vapor pressure). A significant increase (p<0.01) in vapor pressure deficit (VPD) associated with the increase in mean air temperature contributed to increments in ETo along the studied period. The scenario in the entire São Francisco River basin is of increase in the values of the climatic variables, particularly evapotranspiration (85% of basin area with increments) and rainfall (52% of basin area with decrements). Results indicate an increase in ETo variation rates of approximately 2.424 mm year-2, on average, in the entire basin. The energy term represents higher weight in ETo calculation in 81% of the basin territory.

Avaliação de eficiência da implantação de técnica de bioengenharia de solos

O Baixo São Francisco está em constante dinâmica hidroambiental resultante das alterações promovidas na calha do rio, representadas pelos processos geomorfológicos ou por ações antrópicas como a construção das barragens que por sua vez provocou mudanças geomorfológicas resultando na aceleração de processos erosivos nas suas margens. O objetivo deste trabalho foi avaliar a implantação de técnicas de recuperação hidroambiental com uso de bioengenharia de solos na margem do rio São Francisco. A área estudada compreende um trecho do baixo curso do rio São Francisco, localizado no município de Amparo do São Francisco, no estado de Sergipe, nordeste do Brasil, onde técnica de bioengenharia de solos, como enrocamento vegetado, foi implementada no ano de 2011. Três grupos de indicadores individuais foram selecionados que juntos contribuíram para a avaliação da Recuperação da Área Degradada relacionados à qualidade do solo, como resistência do solo à penetração e Velocidade de Infiltração Básica, à recuperação da biodiversidade como banco de sementes e a regeneração natural da área por meio de indicadores como composição e cobertura linear de espécies. A metodologia empregada contempla uma avaliação dos resultados originados do uso da biotécnica a partir da identificação da contribuição da vegetação que auxilia na contenção de taludes, uma vez que a cobertura vegetal protege a superfície do solo contra ações erosivas como o vento e a água da chuva. O reforço mecânico trazido pelo sistema radicular das plantas contra cisalhamento do solo se mostrou pela menor resistência à penetração do solo e maior Taxa de infiltração. Evaluation of efficiency of the implementation of soil bioengineering techniqueA B S T R A C TThe Lower São Francisco is in constant hydro-environmental dynamics resulting from the changes promoted in the river channel, represented by geomorphological processes or by anthropic actions such as the construction of dams that in turn caused geomorphological changes resulting in the acceleration of erosive processes on its banks. The objective of this work was to evaluate the implementation of hydroenvironmental recovery techniques using soil bioengineering on the bank of the São Francisco River. The studied area comprises a stretch of the low course of the São Francisco River, located in the municipality of Amparo do São Francisco, in the state of Sergipe, northeastearn Brazil, where soil bioengineering technique, such as vegetated rockfill, was implemented in 2011. Three groups of individual indicators were selected that together contributed to the assessment of Degraded Area Recovery related to soil quality, such as soil resistance to penetration and Basic Infiltration Speed, to the recovery of biodiversity as a seed bank and the natural area regeneration through indicators such as composition and linear species coverage. The employed methodology includes an evaluation of the results from the use of biotechnology based on the identification of the vegetation contribution that helps to contain slopes, since the vegetation cover protects the soil surface against erosive actions such as wind and rainwater. The mechanical reinforcement brought by the root system against soil shear was shown by the lower resistance to soil penetration and a higher infiltration rate.Keywords: Degraded Areas Recovery, erosion, São Francisco River

Drought Assessment in São Francisco River Basin, Brazil: Characterization through SPI and Associated Anomalous Climate Patterns

The São Francisco River Basin (SFRB) is one of the main watersheds in Brazil, standing out for generating energy and consumption, among other ecosystem services. Hence, it is important to identify hydrological drought events and the anomalous climate patterns associated with dry conditions. The Standard Precipitation Index (SPI) for 12 months was used to identify hydrological drought episodes over SFRB 1979 and 2020. For these episodes, the severity, duration, intensity, and peak were obtained, and SPI-1 was applied for the longest and most severe episode to identify months with wet and dry conditions within the rainy season (Nov–Mar). Anomalous atmospheric and oceanic patterns associated with this episode were also analyzed. The results revealed the longest and most severe hydrological drought episode over the basin occurred between 2012 and 2020. The episode over the Upper portion of the basin lasted 103 months. The results showed a deficit of monthly precipitation up to 250 mm in the southeast and northeast regions of the country during the anomalous dry months identified through SPI-1. The dry conditions observed during the rainy season of this episode were associated with an anomalous high-pressure system acting close to the coast of Southeast Brazil, hindering the formation of precipitating systems.

Operationalizing Water Security Concept in Water Investment Planning: Case Study of São Francisco River Basin

Despite advances in water resources management and planning, the São Francisco River Basin in Brazil has suffered from systematic drought problems in recent years, leading to severe human and environmental water security threats. This paper aims to track the water security for different periods and its relations with the changes in physical and natural asset conditions. The paper explores how investment planning to mitigate the water security threats and explore opportunities to increase the value of investments. The paper finds that grey infrastructure has regulated threats from increasing in the downstream of the river basin, however, continuous increase in water security threats in the upstream of the basin threatens water security downstream. This is evident from the spatial connectivity and unidirection externalities. As the capacity to further increase in grey investment is reaching its limit in the downstream, the increases in green infrastructure investment upstream, especially in the Grande River basin, could be one the way to reduce the externalities and minimise the water security risks.

EROSION CONTROL WITH GEOTEXTILES FROM NATURAL FIBERS IN THE MARGIN OF THE SÃO FRANCISCO RIVER

O baixo rio São Francisco foi impactado por mudanças no fluxo do rio causadas por políticas públicas implementadas nas últimas décadas causadas pela geração de energia elétrica. O objetivo deste trabalho foi avaliar o uso de geotêxteis fabricados a partir de fibras naturais no controle da erosão na margem do rio São Francisco. Geotêxtil , Syagrus coronata Geotêxtil e Bare Soil sem geotêxteis, localizado na margem direita do baixo rio São Francisco, no município de Amparo de São Francisco, estado de Sergipe, nordeste do Brasil. Entre os geotêxteis testados, os geotêxteis Syagrus coronata e Juncus sp foram temporalmente mais eficientes no controle da erosão, produzindo menor quantidade de sedimentos, embora na resistência e durabilidade das fibras, Typha latifolia apresentou melhores resultados.

Effects of the transfer of the São Francisco River waters on the performance of the water treatment plant of Gravatá, Paraíba, Brazil

The objective of this study was to evaluate the effects of the transfer of the São Francisco River waters on the quality of the water produced by water treatment plant of Gravatá (WTP-Gravatá) using multivariate statistics. Monthly means of the variables pH, apparent color and turbidity of raw, decanted and treated waters were used, in addition to the volume accumulated by the Epitácio Pessoa reservoir, during the period from January 2016 to December 2017. The arrival of the transposition waters abruptly changed the apparent color and turbidity of the raw water. In spite of that, the treated water presented low variability of the mentioned parameters, indicating that the WTP-Gravatá was able to adapt its treatment. From the factor analysis/principal component analysis (FA/PCA) it was found that changes in reservoir volume alter the apparent color and turbidity of the raw water, requiring interventions in the coagulation/flocculation/decantation stages. The increasing of these parameters in the decanted water overloads the filtration step, raising the apparent color of the treated water. The cluster analysis distinguished the different phases experienced by the Epitácio Pessoa reservoir. The information obtained can help decision making in WTPs, considering changes in reservoir volumes.