Da recarga não gerenciada à recarga gerenciada: estratégia para aquífero aluvial no semiárido brasileiro.

Grande parcela dos escassos recursos hídricos do semiárido brasileiro estão armazenados nos aquíferos aluviais, servindo como importante fonte para o abastecimento de comunidades rurais e a irrigação de pequeno porte, diante da intermitência dos rios da região. Apesar da importância desses aquíferos, esgoto doméstico, tratado ou não, é depositado nos leitos secos desses rios, gerando uma recarga não gerenciada desses aquíferos que pode provocar impactos negativos, fato que demanda a criação de estratégias em busca de possibilitar o correto manejo desse sistema. Uma opção é realizar a recarga gerenciada desses aquíferos, aproveitando-se da infraestrutura hídrica existente, formada por barragens associadas aos sistemas de tratamento de esgoto. Para formulação de tal estratégia nesse estudo, buscou-se um local que possuísse características representativas da região. Foram levantados dados litológicos e monitorados o nível estático e a qualidade da água do aquífero, assim como sua relação com a precipitação. Dessa forma, o sistema, formado pelo aquífero do Rio Sucuru, o açude Sumé e o esgoto produzido pela cidade de Sumé-PB, foi estudado e observou-se que a concentração de cloreto, utilizado como traçador para indicar a presença de esgoto, manteve-se elevada na zona urbana, devido à falta de saneamento. Porém, tanto seus valores, como a variação deles ao longo do tempo, vão diminuindo com o transcorrer do fluxo subterrâneo. Ainda, em busca de entender a efetividade do tratamento solo-aquífero na região, comparou-se as análises de nutrientes e de indicador bacteriológico do poço com maior presença de cloreto e do esgoto tratado, obtendo-se resultados melhores para o efluente após passagem pelo solo do que pelo sistema de lagoas de estabilização. Apesar dessa aparente capacidade de tratamento do aquífero para tais parâmetros, o mesmo não possui capacidade de remoção de cloreto, o que mostra a necessidade de realizar recarga com águas de menores concentrações, objetivando garantir seus usos e evitar risco de salinização. Diante disso, a estratégia proposta foi dividida em quatro medidas, duas utilizando o esgoto e duas recursos hídricos superficiais, as quais consideram os desafios financeiros e operacionais que podem surgir, de modo a promover: (i) reuso de águas servidas, (ii) diminuir as perdas por evaporação, e, consequentemente, (iii) aumentar a oferta. Sendo assim, essa proposta de promoção da gestão integrada dos recursos hídricos da região atuará no sentido de atingir os objetivos de desenvolvimento do milênio.Great amount of scarce water resources from Brazilian semiarid are stored at alluvial aquifers, serving as important source to supply rural communities and small irrigation, due to its intermittent rivers. Despite the importance of this aquifers, wastewater, treated or not, is disposed at dry riverbed, generating an un-managed aquifer recharge that can lead to negative impacts, demanding creation of strategy searching for correct management of this system. One option is to manage recharge this aquifers, taking advantage of hydric works, made by dams, in conjunction with treated wastewater. To formulate this strategy, a site that possess representative characteristics of the region was chosen, in which lithologic data and of water quality and hydraulic heads were monitored, as their relationship with precipitation. Therefore, the system made by Sucuru River, Sumé Dam and wastewater produced by the city of Sumé, in the State of Paraíba, were studied. It was observed that chloride concentration, used as a tracer to indicate wastewater presence due to lack of sanitation, kept high at the urban zone. However, its values and variation with time decrease along the aquifer. Seeking to understand the effectivity of soil-aquifer treatment, the presence of nutrients and bacteriological indicator were compered between the well with highest amount of chloride and the effluent of the wastewater treatment plant and better results were found for the passage of wastewater through the soil than the system composed by stabilization lagoons. Despite this apparent capacity of treatment from the aquifer, it cannot remove chloride, demonstrating the need to use water with less concentration of this parameter in order to secure its uses and avoid salinization hazard. In face of that, the proposed strategy was divided in four measures, two utilizing wastewater and two superficial water resources available and they consider financial and operational challenges that may occur, in order to promote: (i) water reuse, (ii) reduce evaporation losses and, consequently, (iii) increase offer. This proposal to promote integrated management of existing water resources will act to achieve millennium development goals

Bivariate Modelling of a Teleconnection Index and Extreme Rainfall in a Small North Atlantic Island

This paper explores practical applications of bivariate modelling via copulas of two likely dependent random variables, i.e., of the North Atlantic Oscillation (NAO) coupled with extreme rainfall on the small island of Madeira, Portugal. Madeira, due to its small size (∼740 km2), very pronounced mountain landscape, and location in the North Atlantic, experiences a wide range of rainfall regimes, or microclimates, which hamper the analyses of extreme rainfall. Previous studies showed that the influence of the North Atlantic Oscillation (NAO) on extreme rainfall is at its largest in the North Atlantic sector, with the likelihood of increased rainfall events from December through February, particularly during negative NAO phases. Thus, a copula-based approach was adopted for teleconnection, aiming at assigning return periods of daily values of an NAO index (NAOI) coupled with extreme daily rainfalls—for the period from December 1967 to February 2017—at six representative rain gauges of the island. The results show that (i) bivariate copulas describing the dependence characteristics of the underlying joint distributions may provide useful analytical expressions of the return periods of the coupled previous NAOI and extreme rainfall and (ii) that recent years show signs of increasing climate variability with more anomalous daily negative NAOI along with higher extreme rainfall events. These findings highlight the importance of multivariate modelling for teleconnections of prominent patterns of climate variability, such as the NAO, to extreme rainfall in North Atlantic regions, especially in small islands that are highly vulnerable to the effects of abrupt climate variability

A Continuous Drought Probability Monitoring System, CDPMS, Based on Copulas

The standardized precipitation index (SPI), is one of the most used drought indices. However, it is difficult to use to monitor the ongoing drought characteristics because it cannot be expeditiously related to precipitation deficits. It also does not provide information regarding the drought probability nor the temporal evolution of the droughts. By assigning the SPI to drought-triggering precipitation thresholds, a copula-based continuous drought probability monitoring system (CDPMS), was developed aiming to monitor the probability of having a drought as the rainy season advances. In fact, in climates with very pronounced rainy seasonality, the absence of precipitation during the rainy season is the fundamental cause of droughts. After presenting the CDPMS, we describe its application to Mainland Portugal and demonstrate that the system has an increased capability of anticipating drought probability by the end of the rainy season as new precipitation records are collected. The good performance of the system results from the ability of the copula to model complex dependence structures as those existing between precipitations at different time intervals. CDPMS is an innovative and user-friendly tool to monitor precipitation and, consequently, the drought probability, allowing the user to anticipate mitigation and adaptation measures, or even to issue alerts

Copula-Based Multivariate Frequency Analysis of the 2012–2018 Drought in Northeast Brazil

The 2012–2018 drought was such an extreme event in the drought-prone area of Northeast Brazil that it triggered a discussion about proactive drought management. This paper aims at understanding the causes and consequences of this event and analyzes its frequency. A consecutive sequence of sea surface temperature anomalies in the Pacific and Atlantic Oceans, at both the decadal and interannual scales, led to this severe and persistent drought. Drought duration and severity were analyzed using run theory at the hydrographic region scale as decision-makers understand impact analysis better at this scale. Copula functions were used to properly model drought joint characteristics as they presented different marginal distributions and an asymmetric behavior. The 2012–2018 drought in Ceará State had the highest mean bivariate return period ever recorded, estimated at 240 years. Considering drought duration and severity simultaneously at the level of the hydrographic regions improves risk assessment. This result advances our understanding of exceptional events. In this sense, the present work proposes the use of this analysis as a tool for proactive drought planning

Jointly Modeling Drought Characteristics with Smoothed Regionalized SPI Series for a Small Island

The paper refers to a study on droughts in a small Portuguese Atlantic island, namely Madeira. The study aimed at addressing the problem of dependent drought events and at developing a copula-based bivariate cumulative distribution function for coupling drought duration and magnitude. The droughts were identified based on the Standardized Precipitation Index (SPI) computed at three and six-month timescales at 41 rain gauges distributed over the island and with rainfall data from January 1937 to December 2016. To remove the spurious and short duration-dependent droughts a moving average filter (MA) was used. The run theory was applied to the smoothed SPI series to extract the drought duration, magnitude, and interarrival time for each drought category. The smoothed series were also used to identify homogeneous regions based on principal components analysis (PCA). The study showed that MA is necessary for an improved probabilistic interpretation of drought analysis in Madeira. It also showed that despite the small area of the island, three distinct regions with different drought temporal patterns can be identified. The copulas approach proved that the return period of droughts events can differ significantly depending on the way the relationship between drought duration and magnitude is accounted for

Use of Machine Learning in Evaluation of Drought Perception in Irrigated Agriculture: The Case of an Irrigated Perimeter in Brazil

This study aimed to understand the perception of drought among farmers, in order to support decision-making in the water allocation process. This study was carried out in the Tabuleiro de Russas irrigated perimeter, in northeast Brazil, over the drought period of 2012–2018. Two analyses were conducted: (i) drought characterization, using the Standardized Precipitation Index (SPI) based on drought duration and frequency criteria; and (ii) analysis of farmers’ perceptions of drought via selection of explanatory variables using the Random Forest (RF) and the Decision Tree (DT) methods. The 2012–2018 drought period was defined as a meteorological phenomenon by local farmers; however, an SPI evaluation indicated that the drought was of a hydrological nature. According to the RF analysis, four of the nine study variables were more statistically important than the others in influencing farmers’ perception of drought: number of cultivated land plots, farmer’s age, years of experience in the agriculture sector, and education level. These results were confirmed using DT analysis. Understanding the relationship between these variables and farmers’ perception of drought could aid in the development of an adaptation strategy to water deficit scenarios. Farmers’ perception can be beneficial in reducing conflicts, adopting proactive management practices, and developing a holistic and efficient early warning drought system

Flash Flood Reconstruction and Analysis—A Case Study Using Social Data

This work proposes a methodology for post-flood analysis in ungauged basins with low data availability located in semi-arid regions. The methodology combines social perception with recorded data. Social perception can be a useful tool to enhance the modeling process in cases where official records are nonexistent or unsatisfactory. For this aim, we structured a four-step methodology. First, we create a repository with the information that reconstructs the analyzed event. Photos and news of the flood event are collected from social media platforms. The next step is to consult official government agencies to obtain documented information about the disaster. Then, semi-structured interviews are carried out with residents to obtain the extension and depth of the flooded spot. This social information creates an overview of the flood event that can be used to evaluate the hydraulic/hydrological modeling of the flood event and the quality of the recorded data. We analyzed a flood event in a city in semi-arid Brazil. The event caused several damages such as the breaking of dams and about 40% of the population was somehow impacted although the official rain data pointed to non-extreme precipitation